ACP - Annual exposure to polycyclic aromatic hydrocarbons in urban environments linked to wintertime wood-burning episodes

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name="citation_fulltext_world_readable" content=""> <meta name="citation_publisher" content="Copernicus GmbH"/> <meta name="citation_title" content="Annual exposure to polycyclic aromatic hydrocarbons in urban environments linked to wintertime wood-burning episodes"/> <meta name="citation_abstract" content="<p><strong class="journal-contentHeaderColor">Abstract.</strong> Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants in fine particulate matter (PM) long known to have mutagenic and carcinogenic effects, but much is unknown about the importance of local and remote sources for PAH levels observed in population-dense urban environments. A year-long sampling campaign in Athens, Greece, where more than 150 samples were analyzed for 31 PAHs and a wide range of chemical markers, was combined with positive matrix factorization (PMF) to constrain the temporal variability, sources, and carcinogenic risk associated with PAHs. It was found that biomass burning (BB), a source mostly present during wintertime intense pollution events (observed for 18 <span class="inline-formula">%</span> of measurement days in 2017), led to wintertime PAH levels that were 7 times higher than in other seasons and was as important for annual mean PAH concentrations (31 <span class="inline-formula">%</span>) as diesel and oil (33 <span class="inline-formula">%</span>) and gasoline (29 <span class="inline-formula">%</span>) sources. The contribution of non-local sources, although limited on an annual basis (7 <span class="inline-formula">%</span>), increased during summer, becoming comparable to that of local sources combined. The fraction of PAHs (12 members that were included in the PMF analysis) that was associated with BB was also linked to increased health risk compared to the other sources, accounting for almost half the annual PAH carcinogenic potential (43 <span class="inline-formula">%</span>). This can result in a large number of excess cancer cases due to BB-related high PM levels and urges immediate action to reduce residential BB emissions in urban areas facing similar issues.</p>"/> <meta name="citation_publication_date" content="2021/12/07"/> <meta name="citation_online_date" content="2021/12/07"/> <meta name="citation_journal_title" content="Atmospheric Chemistry and Physics"/> <meta name="citation_volume" content="21"/> <meta name="citation_issue" content="23"/> <meta name="citation_issn" content="1680-7316"/> <meta name="citation_doi" content="https://doi.org/10.5194/acp-21-17865-2021"/> <meta name="citation_firstpage" content="17865"/> <meta name="citation_lastpage" content="17883"/> <meta name="citation_author" content="Tsiodra, Irini"/> <meta name="citation_author_institution" content="Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, Heraklion, 71003, Greece"/> <meta name="citation_author_institution" content="Center for the Study of Air Quality and Climate Change, Institute of Chemical Engineering Sciences, Foundation for Research and Technology Hellas, Patras, 26504, Greece"/> <meta name="citation_author_orcid" content="0000-0001-5392-8986"> <meta name="citation_author" content="Grivas, Georgios"/> <meta name="citation_author_institution" content="Institute for Environmental Research and Sustainable Development, National Observatory of Athens, Lofos Koufou, Palea Penteli, Athens, 15236, Greece"/> <meta name="citation_author" content="Tavernaraki, Kalliopi"/> <meta name="citation_author_institution" content="Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, Heraklion, 71003, Greece"/> <meta name="citation_author" content="Bougiatioti, Aikaterini"/> <meta name="citation_author_institution" content="Institute for Environmental Research and Sustainable Development, National Observatory of Athens, Lofos Koufou, Palea Penteli, Athens, 15236, Greece"/> <meta name="citation_author" content="Apostolaki, Maria"/> <meta name="citation_author_institution" content="Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, Heraklion, 71003, Greece"/> <meta name="citation_author" content="Paraskevopoulou, Despina"/> <meta name="citation_author_institution" content="Institute for Environmental Research and Sustainable Development, National Observatory of Athens, Lofos Koufou, Palea Penteli, Athens, 15236, Greece"/> <meta name="citation_author_institution" content="Center for the Study of Air Quality and Climate Change, Institute of Chemical Engineering Sciences, Foundation for Research and Technology Hellas, Patras, 26504, Greece"/> <meta name="citation_author_orcid" content="0000-0002-8482-4925"> <meta name="citation_author" content="Gogou, Alexandra"/> <meta name="citation_author_institution" content="Institute of Oceanography, Hellenic Centre for Marine Research, Anavyssos, 19013, Greece"/> <meta 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"> <meta name="citation_funding_source" content="citation_funder=H2020 European Research Council;citation_funder_id=100010663;citation_grant_number=726165"> <meta name="citation_funding_source" content="citation_funder=Hellenic Ministry of Environment and Energy;citation_funder_id=100016585;citation_grant_number=PANhellenic infrastructure for Atmospheric Composition and climatE change (MIS 5021516)"> <meta name="citation_pdf_url" content="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021.pdf"/> <meta name="citation_xml_url" content="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021.xml"/> <meta name="fulltext_pdf" content="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021.pdf"/> <meta name="citation_language" content="English"/> <meta name="libraryUrl" content="https://acp.copernicus.org/articles/"/> <meta property="og:image" content="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-avatar-web.png"/> <meta property="og:title" content="Annual exposure to polycyclic aromatic hydrocarbons in urban environments linked to wintertime wood-burning episodes"> <meta property="og:description" content="Abstract. Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants in fine particulate matter (PM) long known to have mutagenic and carcinogenic effects, but much is unknown about the importance of local and remote sources for PAH levels observed in population-dense urban environments. A year-long sampling campaign in Athens, Greece, where more than 150 samples were analyzed for 31 PAHs and a wide range of chemical markers, was combined with positive matrix factorization (PMF) to constrain the temporal variability, sources, and carcinogenic risk associated with PAHs. It was found that biomass burning (BB), a source mostly present during wintertime intense pollution events (observed for 18 % of measurement days in 2017), led to wintertime PAH levels that were 7 times higher than in other seasons and was as important for annual mean PAH concentrations (31 %) as diesel and oil (33 %) and gasoline (29 %) sources. The contribution of non-local sources, although limited on an annual basis (7 %), increased during summer, becoming comparable to that of local sources combined. The fraction of PAHs (12 members that were included in the PMF analysis) that was associated with BB was also linked to increased health risk compared to the other sources, accounting for almost half the annual PAH carcinogenic potential (43 %). This can result in a large number of excess cancer cases due to BB-related high PM levels and urges immediate action to reduce residential BB emissions in urban areas facing similar issues."> <meta property="og:url" content="https://acp.copernicus.org/articles/21/17865/2021/"> <meta property="twitter:image" content="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-avatar-web.png"/> <meta name="twitter:card" content="summary_large_image"> <meta name="twitter:title" content="Annual exposure to polycyclic aromatic hydrocarbons in urban environments linked to wintertime wood-burning episodes"> <meta name="twitter:description" content="Abstract. Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants in fine particulate matter (PM) long known to have mutagenic and carcinogenic effects, but much is unknown about the importance of local and remote sources for PAH levels observed in population-dense urban environments. A year-long sampling campaign in Athens, Greece, where more than 150 samples were analyzed for 31 PAHs and a wide range of chemical markers, was combined with positive matrix factorization (PMF) to constrain the temporal variability, sources, and carcinogenic risk associated with PAHs. It was found that biomass burning (BB), a source mostly present during wintertime intense pollution events (observed for 18 % of measurement days in 2017), led to wintertime PAH levels that were 7 times higher than in other seasons and was as important for annual mean PAH concentrations (31 %) as diesel and oil (33 %) and gasoline (29 %) sources. The contribution of non-local sources, although limited on an annual basis (7 %), increased during summer, becoming comparable to that of local sources combined. The fraction of PAHs (12 members that were included in the PMF analysis) that was associated with BB was also linked to increased health risk compared to the other sources, accounting for almost half the annual PAH carcinogenic potential (43 %). This can result in a large number of excess cancer cases due to BB-related high PM levels and urges immediate action to reduce residential BB emissions in urban areas facing similar issues."> <link rel="icon" href="https://www.atmospheric-chemistry-and-physics.net/favicon.ico" type="image/x-icon"/> <script type="text/javascript" src="https://cdn.copernicus.org/libraries/jquery/1.11.1/ui/jquery-ui.min.js"></script> <script type="text/javascript" src="https://cdn.copernicus.org/libraries/jquery/1.11.1/ui/jquery-ui-slider-pips.js"></script> <script type="text/javascript" src="https://cdn.copernicus.org/libraries/jquery/1.11.1/ui/template_jquery-ui-touch.min.js"></script> <script type="text/javascript" src="https://cdn.copernicus.org/js/respond.js"></script> <script type="text/javascript" src="https://cdn.copernicus.org/libraries/highstock/2.0.4/highstock.js"></script> <script type="text/javascript" src="https://cdn.copernicus.org/apps/htmlgenerator/js/CoPublisher.js"></script> <script 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id="breadcrumbs_content_container"><div id="cmsbox_1088152" class="cmsbox ">  <ol class="breadcrumb"> <li class="breadcrumb-item"><a href="https://acp.copernicus.org/">Articles</a></li><li class="breadcrumb-item"><a href="https://acp.copernicus.org/articles/21/issue23.html">Volume 21, issue 23</a></li><li class="breadcrumb-item active">ACP, 21, 17865–17883, 2021</li> </ol>  </div></div> <div class="col col-md-4 text-right page-search CMSCONTAINER" id="search_content_container"><div id="cmsbox_1088035" class="cmsbox ">       <div class="pswp" tabindex="-1" role="dialog" aria-hidden="true" >  <div class="pswp__bg"></div>  <div class="pswp__scroll-wrap">  <div class="pswp__container"> <div class="pswp__item"></div> <div class="pswp__item"></div> <div class="pswp__item"></div> </div>  <div class="pswp__ui pswp__ui--hidden"> <div class="pswp__top-bar">  <div class="pswp__counter"></div> <button class="pswp__button pswp__button--close" title="Close (Esc)"></button> <button 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type="search" placeholder="Search" name="q" class="form-control form-control-sm" id="search_query_solr"/> </div> <div class="col-auto pl-0"> <button title="Start site search" id="start_site_search_solr" class="btn btn-sm btn-success"><span class="co-search"></span></button> </div> </div> <div class="text-left"> <div id="templateSearchInfo" class="d-none"> <div> <p> Multiple terms: term1 term2<br /> <i>red apples</i><br /> returns results with all terms like:<br /> <i>Fructose levels in <strong>red</strong> and <strong>green</strong> apples</i><br /> </p> <p> Precise match in quotes: "term1 term2"<br /> <i>"red apples"</i><br /> returns results matching exactly like:<br /> <i>Anthocyanin biosynthesis in <strong>red apples</strong></i><br /> </p> <p> Exclude a term with -: term1 -term2<br /> <i>apples -red</i><br /> returns results containing <i><strong>apples</strong></i> but not <i><strong>red</strong></i>:<br /> <i>Malic acid in green <strong>apples</strong></i><br /> </p> </div> </div> <div class="modal " id="templateSearchResultModal" role="dialog" aria-labelledby="Search results" aria-hidden="true"> <div class="modal-dialog modal-lg modal-dialog-centered"> <div class="modal-content"> <div class="modal-header modal-header--sticky shadow one-column d-block"> <div class="row no-gutters mx-1"> <div class="col mr-3"> <h1 class="" id="resultsSearchHeader"><span id="templateSearchResultNr"></span> hit<span id="templateSearchResultNrPlural">s</span> for <span id="templateSearchResultTerm"></span></h1> </div> <div class="col-auto"> <a id="scrolltopmodal" href="javascript:void(0)" onclick="scrollModalTop();" style="display: none;"><i class="co-home"></i></a> </div> <div class="col-auto"> <button data-dismiss="modal" aria-label="Close" class="btn btn-danger mt-1">Close</button> </div> </div> </div> <div class="modal-body one-column">  <div class="grid-container mx-n3"><div class="grid-85 tablet-grid-85"> <button aria-label="Refine" id="refineSearchModal" class="btn btn-primary float-left mt-4">Refine your search</button> <button aria-label="Refine" id="refineSearchModalHide" class="btn btn-danger float-left d-none mt-4">Hide refinement</button> </div></div> <div class="grid-container mx-n3"><div class="grid-100 tablet-grid-100"><div id="templateRefineSearch" class="d-none"></div></div></div> <div id="templateSearchResultContainer" class="searchResultsModal mx-n3"></div> <div class="grid-container mb-0"><div class="grid-100 tablet-grid-100"><div id="templateSearchResultContainerEmpty" class="co-notification d-none">There are no results for your search term.</div></div></div> </div> </div> </div> </div> </div>  <div class="modal " id="templateSearchErrorModal1" role="dialog" aria-labelledby="Search results" aria-hidden="true"> <div class="modal-dialog modal-lg modal-dialog-centered"> <div class="modal-content p-3"> <div class="modal-body text-left"> <h1 class="mt-0 pt-0">Network problems</h1> <div class="co-error">We are sorry, but your search could not be completed due to network problems. Please try again later.</div> </div> </div> </div> </div>  <div class="modal " id="templateSearchErrorModal2" role="dialog" aria-labelledby="Search results" aria-hidden="true"> <div class="modal-dialog modal-lg modal-dialog-centered"> <div class="modal-content p-3"> <div class="modal-body text-left"> <h1 class="mt-0 pt-0">Server timeout</h1> <div class="co-error">We are sorry, but your search could not be completed due to server timeouts. Please try again later.</div> </div> </div> </div> </div>  <div class="modal " id="templateSearchErrorModal3" role="dialog" aria-labelledby="Search results" aria-hidden="true"> <div class="modal-dialog modal-lg modal-dialog-centered"> <div class="modal-content p-3"> <div class="modal-body text-left"> <h1 class="mt-0 pt-0">Empty search term</h1> <div class="co-error">You have applied the search with an empty search term. Please revisit and try again.</div> </div> </div> </div> </div>  <div class="modal " id="templateSearchErrorModal4" role="dialog" aria-labelledby="Search results" aria-hidden="true"> <div class="modal-dialog modal-lg modal-dialog-centered"> <div class="modal-content p-3"> <div class="modal-body text-left"> <h1 class="mt-0 pt-0">Too many requests</h1> <div class="co-error">We are sorry, but we have received too many parallel search requests. Please try again later.</div> </div> </div> </div> </div>  <div class="modal " id="templateSearchLoadingModal" role="dialog" aria-labelledby="Search results" aria-hidden="true"> <div class="modal-dialog modal-sm modal-dialog-centered"> <div class="modal-content p-3 co_LoadingDotsContainer"> <div class="modal-body"> <div class="text">Searching</div> <div class="dots d-flex justify-content-center"><div class="dot"></div><div class="dot"></div><div class="dot"></div></div></div> </div> </div> </div> </div> <style> /*.modal {*/ /* background: rgba(255, 255, 255, 0.8);*/ /*}*/ .modal-header--sticky { position: sticky; top: 0; background-color: inherit; z-index: 1055; } .grid-container { margin-bottom: 1em; /*padding-left: 0;*/ /*padding-right: 0;*/ } #templateSearchInfo{ display: none; background-color: var(--background-color-primary); margin-top: 1px; z-index: 5; border: 1px solid var(--color-primary); opacity: .8; font-size: .7rem; border-radius: .25rem; } #templateSearchLoadingModal .co_LoadingDotsContainer { z-index: 1000; } #templateSearchLoadingModal .co_LoadingDotsContainer .text { text-align: center; font-weight: bold; padding-bottom: 1rem; } #templateSearchLoadingModal .co_LoadingDotsContainer .dot { background-color: #0072BC; border: 2px solid white; border-radius: 50%; float: left; height: 2rem; width: 2rem; margin: 0 5px; -webkit-transform: scale(0); transform: scale(0); -webkit-animation: animation_dots_breath 1000ms ease infinite 0ms; animation: animation_dots_breath 1000ms ease infinite 0ms; } #templateSearchLoadingModal .co_LoadingDotsContainer .dot:nth-child(2) { -webkit-animation: animation_dots_breath 1000ms ease infinite 300ms; animation: animation_dots_breath 1000ms ease infinite 300ms; } #templateSearchLoadingModal .co_LoadingDotsContainer .dot:nth-child(3) { -webkit-animation: animation_dots_breath 1000ms ease infinite 600ms; animation: animation_dots_breath 1000ms ease infinite 600ms; } #templateSearchResultModal [class*="grid-"] { padding-left: 10px !important; padding-right: 10px !important; } #templateSearchResultTerm { font-weight: bold; } #resultsSearchHeader { display: block !important; } #scrolltopmodal { font-size: 3.0em; margin-top: 0 !important; margin-right: 15px; } @-webkit-keyframes animation_dots_breath { 50% { -webkit-transform: scale(1); transform: scale(1); opacity: 1; } 100% { opacity: 0; } } @keyframes animation_dots_breath { 50% { -webkit-transform: scale(1); transform: scale(1); opacity: 1; } 100% { opacity: 0; } } @media (min-width: 768px) and (max-width: 991px) { #templateSearchResultModal .modal-dialog { max-width: 90%; } } </style> <script> if(document.querySelector('meta[name="global_moBaseURL"]').content == "https://meetingorganizer.copernicus.org/") FINDER_URL = document.querySelector('meta[name="global_moBaseURL"]').content.replace('meetingorganizer', 'finder-app')+"search/library.php"; else FINDER_URL = document.querySelector('meta[name="global_moBaseURL"]').content.replace('meetingorganizer', 'finder')+"search/library.php"; SEARCH_INPUT = document.getElementById('search_query_solr'); SEARCH_INPUT_MODAL = document.getElementById('search_query_modal'); searchRunning = false; offset = 20; INITIAL_OFFSET = 20; var MutationObserver = window.MutationObserver || window.WebKitMutationObserver || window.MozMutationObserver; const targetNodeSearchModal = document.getElementById("templateSearchResultModal"); const configSearchModal = { attributes: true, childList: true, subtree: true }; // Callback function to execute when mutations are observed const callbackSearchModal = (mutationList, observer) => { for (const mutation of mutationList) { if (mutation.type === "childList") { // console.log("A child node has been added or removed."); picturesGallery(); } else if (mutation.type === "attributes") { // console.log(`The ${mutation.attributeName} attribute was modified.`); } } }; // Create an observer instance linked to the callback function const observer = new MutationObserver(callbackSearchModal); // Start observing the target node for configured mutations observer.observe(targetNodeSearchModal, configSearchModal); function _addEventListener() { document.getElementById('search_query_solr').addEventListener('keypress', (e) => { if (e.key === 'Enter') _runSearch(); }); document.getElementById('start_site_search_solr').addEventListener('click', (e) => { _runSearch(); e.stopPropagation(); e.stopImmediatePropagation(); return false; }); $('#templateSearchResultModal').scroll(function() { if ($(this).scrollTop()) { $('#scrolltopmodal:hidden').stop(true, true).fadeIn().css("display","inline-block"); } else { $('#scrolltopmodal').stop(true, true).fadeOut(); } }); } function scrollModalTop() { $('#templateSearchResultModal').animate({ scrollTop: 0 }, 'slow'); // $('#templateSearchResultModal').scrollTop(0); } function picturesGallery() { $('body').off('click', '.paperlist-avatar img'); $('body').off('click', '#templateSearchResultContainer .paperlist-avatar img'); searchPaperListAvatar = []; searchPaperListAvatarThumb = []; search_pswpElement = document.querySelectorAll('.pswp')[0]; if (typeof search_gallery != "undefined") { search_gallery = null; } $('body').on('click', '#templateSearchResultContainer .paperlist-avatar img', function (e) { if(searchPaperListAvatarThumb.length === 0 && searchPaperListAvatar.length === 0) { $('#templateSearchResultContainer .paperlist-avatar img').each(function () { var webversion = $(this).attr('data-web'); var width = $(this).attr('data-width'); var height = $(this).attr('data-height'); var caption = $(this).attr('data-caption'); var figure = { src: webversion, w: width, h: height, title: caption }; searchPaperListAvatarThumb.push($(this)[0]); searchPaperListAvatar.push(figure); }); } var target = $(this); var index = $('#templateSearchResultContainer .paperlist-avatar img').index(target); var options = { showHideOpacity:false, bgOpacity:0.8, index:index, spacing:0.15, history: false, focus:false, getThumbBoundsFn: function(index) { var thumbnail = searchPaperListAvatarThumb[index]; var pageYScroll = window.pageYOffset || document.documentElement.scrollTop; var rect = thumbnail.getBoundingClientRect(); return {x:rect.left, y:rect.top + pageYScroll, w:rect.width}; } }; search_gallery = new PhotoSwipe( search_pswpElement, PhotoSwipeUI_Default,[searchPaperListAvatar[index]],options); search_gallery.init(); }); } function showError(code, msg) { console.error(code, msg); $("#templateSearchLoadingModal").modal("hide"); switch(code) { case -3: // http request fail case -2: // invalid MO response case 4: // CORS case 1: // project $("#templateSearchErrorModal1").modal({}); break; case -1: // timeout $("#templateSearchErrorModal2").modal({}); break; case 2: // empty term $("#templateSearchErrorModal3").modal({}); break; case 3: // DOS $("#templateSearchErrorModal4").modal({}); break; default: $("#templateSearchErrorModal1").modal({}); break; } } function clearForm() { var myFormElement = document.getElementById("library-filters") var elements = myFormElement.elements; $(".form-check-input").prop('checked', false).change().parent().removeClass('active'); for(i=0; i<elements.length; i++) { field_type = elements[i].type.toLowerCase(); switch(field_type) { case "text": case "password": case "textarea": case "hidden": elements[i].value = ""; break; case "radio": case "checkbox": if (elements[i].checked) { elements[i].checked = false; } break; case "select-one": case "select-multi": elements[i].selectedIndex = -1; break; default: break; } } } function generateShowMoreButton(offset, term) { var code = '<button aria-label="ShowMore" id="showMore" class="btn btn-success float-right mr-2" data-offset="' + offset + '">Show more</button>'; return code; } function hideModal(id) { $("#"+id).modal('hide'); } function showModal(id) { $("#"+id).modal({}); } function prepareForPhotoSwipe() { searchPaperListAvatar = []; searchPaperListAvatarThumb = []; search_pswpElement = document.querySelectorAll('.pswp')[0]; } function _sendAjax(projectID, term) { let httpRequest = new XMLHttpRequest(); if(searchRunning) { console.log("Search running"); return; } if (!httpRequest) { console.error("Giving up :( Cannot create an XMLHTTP instance"); showError(-1); return false; } // httpRequest.timeout = 20000; // time in milliseconds httpRequest.withCredentials = false; httpRequest.ontimeout = (e) => { showError(-1, "result timeout"); searchRunning = false; }; httpRequest.onreadystatechange = function() { if (httpRequest.readyState === XMLHttpRequest.DONE) { searchRunning = false; if (httpRequest.status === 200) { let rs = JSON.parse(httpRequest.responseText); if(rs) { if(rs.isError) { showError(rs.errorCode, rs.errorMessage); } else { let html = rs.resultHTMLs; $("#modal_search_query").val(rs.term); $("#templateSearchResultTerm").html(rs.term); $("#templateSearchResultNr").html(rs.resultsNr); $("#templateRefineSearch").html(rs.filter); if(rs.filter == false) { console.log('filter empty'); $("#refineSearchModal").removeClass('d-block').addClass('d-none'); } if(rs.resultsNr==1) $("#templateSearchResultNrPlural").hide(); else $("#templateSearchResultNrPlural").show(); if(rs.resultsNr==0) { hideModal('templateSearchLoadingModal'); $("#templateSearchResultContainer").html(""); $("#templateSearchResultContainerEmpty").removeClass("d-none"); showModal('templateSearchResultModal'); } else { if((rs.resultsNr - offset)>0) { html = html + generateShowMoreButton(offset, term); } $("#templateSearchResultContainerEmpty").addClass("d-none"); if( offset == INITIAL_OFFSET) { hideModal('templateSearchLoadingModal'); $("#templateSearchResultContainer").html(html); showModal('templateSearchResultModal'); } else { $('#showMore').remove(); startHtml = $("#templateSearchResultContainer").html(); $("#templateSearchResultContainer").html(startHtml + html); } // prepareForPhotoSwipe(); } } } else { showError(-2, "invalid result"); } } else { showError(-3, "There was a problem with the request."); } } }; if(offset == INITIAL_OFFSET) { hideModal('templateSearchResultModal'); showModal('templateSearchLoadingModal'); } httpRequest.open("GET", FINDER_URL+"?project="+projectID+"&term="+encodeURI(term)+((offset>INITIAL_OFFSET)?("&offset="+(offset-INITIAL_OFFSET)) : "")); httpRequest.send(); searchRunning = true; } function _runSearch() { var projectID = document.querySelector('meta[name="global_projectID"]').content; var term = _searchTrimInput(SEARCH_INPUT.value); if(term.length > 0) { _sendAjax(projectID, term); } else { showError(2, 'Empty search term') } } function _searchTrimInput(str) { return str.replace(/^\s+|\s+$/gm, ''); } function run() { _addEventListener(); $('#templateSearchInfoBtn, #modalSearchInfoBtn').popover({ sanitize: false, html: true, content: $("#templateSearchInfo").html(), placement: "bottom", template: '<div class="popover" role="tooltip"><div class="arrow"></div><button class="m-1 float-right btn btn-sm btn-danger" id="templateSearchInfoClose"><i class="fas fa-times-circle"></i></button><h3 class="popover-header"></h3><div class="popover-body"></div></div>', title: "Search tips", }); $(document).click(function (e) { let t = $(e.target); let a = t && t.attr("data-toggle")!=="popover" && t.parent().attr("data-toggle")!=="popover"; let b = t && $(".popover").has(t).length===0; if(a && b) { $('#templateSearchInfoBtn').popover('hide'); $('#modalSearchInfoBtn').popover('hide'); } }); $('#templateSearchInfoBtn').on('shown.bs.popover', function () { $("#templateSearchInfoClose").click(function(e){ $('#templateSearchInfoBtn').popover('hide'); e.stopPropagation(); e.stopImmediatePropagation(); return false; }); }) $('#templateSearchResultModal').on('hidden.bs.modal', function(e) { $('body').off('click', '#templateSearchResultContainer .paperlist-avatar img'); var pswpElement = document.querySelectorAll('.pswp')[0]; var gallery = null; var paperListAvatar = []; var paperListAvatarThumb = []; $('.paperlist-avatar img').each(function(){ var webversion = $(this).attr('data-web'); var width = $(this).attr('data-width'); var height = $(this).attr('data-height'); var caption =$(this).attr('data-caption'); var figure = { src:webversion, w:width, h:height, title:caption }; paperListAvatarThumb.push($(this)[0]); paperListAvatar.push(figure); }); $('body').on('click', '.paperlist-avatar img', function (e) { if(paperListAvatarThumb.length === 0 && paperListAvatar.length === 0){ $('.paperlist-avatar img').each(function(){ var webversion = $(this).attr('data-web'); var width = $(this).attr('data-width'); var height = $(this).attr('data-height'); var caption =$(this).attr('data-caption'); var figure = { src:webversion, w:width, h:height, title:caption }; paperListAvatarThumb.push($(this)[0]); paperListAvatar.push(figure); }); } var target = $(this); var index = $('.paperlist-avatar img').index(target); var options = { showHideOpacity:true, bgOpacity:0.8, index:index, spacing:0.15, getThumbBoundsFn: function(index) { var thumbnail = paperListAvatarThumb[index]; var pageYScroll = window.pageYOffset || document.documentElement.scrollTop; var rect = thumbnail.getBoundingClientRect(); return {x:rect.left, y:rect.top + pageYScroll, w:rect.width}; } }; gallery = new PhotoSwipe( pswpElement, PhotoSwipeUI_Default,[paperListAvatar[index]],options); gallery.init(); }); }); $('#templateSearchResultModal').on('hide.bs.modal', function(e) { $("#templateRefineSearch").removeClass('d-block').addClass('d-none'); $("#refineSearchModalHide").removeClass('d-block').addClass('d-none'); $("#refineSearchModal").removeClass('d-none').addClass('d-block'); offset = INITIAL_OFFSET; }) $(document).on("click", "#showMore", function(e){ offset+=INITIAL_OFFSET; runSearchModal() e.stopPropagation(); e.stopImmediatePropagation(); return false; }); $(document).ready(function() { $(document).on("click", "#refineSearchModal", function (e) { $("#templateRefineSearch").removeClass('d-none').addClass('d-block'); $(this).removeClass('d-block').addClass('d-none'); $("#refineSearchModalHide").removeClass('d-none').addClass('d-block'); }); $(document).on("click", "#refineSearchModalHide", function (e) { $("#templateRefineSearch").removeClass('d-block').addClass('d-none'); $(this).removeClass('d-block').addClass('d-none'); $("#refineSearchModal").removeClass('d-none').addClass('d-block'); }); $(document).on("click", "#modal_start_site_search", function (e) { runSearchModal(); e.stopPropagation(); e.stopImmediatePropagation(); return false; }); }); } function runSearchModal() { var projectID = document.querySelector('meta[name="global_projectID"]').content; var queryString = $('#library-filters').serialize(); var term = _searchTrimInput($('#modal_search_query').val()); term+='&'+queryString; if(term.length > 0) { _sendAjax(projectID, term); } else { showError(2, 'Empty search term') } } if(document.getElementById('search_query_solr')) { run(); } </script> </div></div> </div> </div> </div> </div> </header>  <main class="one-column version-2023"> <div id="content" class="container"> <div id="page_content_container" class="CMSCONTAINER row"> <div class="col"> <div class="article"> <div id="top"></div> <div class="row no-gutters header-block mb-1 align-items-end"> <div class="col-12 col-xl-5"> <div class="row d-xl-none mb-3"> <div class="col-12" > <div class="d-none d-lg-block articleBackLink"> <a href="https://acp.copernicus.org/">Articles</a> | <a href="https://acp.copernicus.org/articles/21/issue23.html">Volume 21, issue 23</a> </div> <div class="tab co-angel-left d-md-none"></div> <div class="tab co-angel-right d-md-none"></div> <div class="mobile-citation"> <ul class="tab-navigation no-styling"> <li class="tab1.articlf active"><nobr><a href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021.html">Article</a></nobr></li><li class="tab3.discussioo"><nobr><a href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-discussion.html">Peer review</a></nobr></li><li class="tab450.metrict"><nobr><a href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-metrics.html">Metrics</a></nobr></li><li class="tab500.relationt"><nobr><a href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-relations.html">Related articles</a></nobr></li> </ul> </div> </div> </div> <div class="d-lg-none"> <span class="articleBackLink"><a href="https://acp.copernicus.org/">Articles</a> | <a href="https://acp.copernicus.org/articles/21/issue23.html">Volume 21, issue 23</a> </span> <div class="citation-header" id="citation-content"> <div class="citation-doi">https://doi.org/10.5194/acp-21-17865-2021</div> <div class="citation-copyright">© Author(s) 2021. 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Distributed under the Creative Commons Attribution 4.0 License." data-web="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-avatar-web.png" data-width="600" data-height="280"> </a> <h1>Annual exposure to polycyclic aromatic hydrocarbons in urban environments linked to wintertime wood-burning episodes</h1> <div class="auto-fixed-top-forced article-title"> <div class="grid-container show-on-fixed" style="display: none"> <div class="grid-85 mobile-grid-85 tablet-grid-85 grid-parent"> <span class="d-block hide-on-mobile hide-on-tablet journal-contentHeaderColor">Annual exposure to polycyclic aromatic hydrocarbons in urban environments linked to wintertime wood-burning episodes</span> <span class="d-block hide-on-desktop journal-contentHeaderColor">Annual exposure to polycyclic aromatic hydrocarbons in urban environments linked to wintertime...</span> <span>Irini Tsiodra et al.</span> </div> <div class="grid-1 mobile-grid-15 tablet-grid-15 grid-parent text-right"> <a id="scrolltop" class="scrollto" href="https://acp.copernicus.org/articles/21/17865/2021/#top"><i class="co-home"></i> </a> </div> </div> </div> <div class="mb-3 authors-with-affiliations"> <nobr><span class="hover-cursor-pointer journal-contentLinkColor hover-underline" data-toggle="modal" data-target=".author711175">Irini Tsiodra</span>,</nobr> <nobr><span class="hover-cursor-pointer journal-contentLinkColor hover-underline" data-toggle="modal" data-target=".author711176">Georgios Grivas</span>,</nobr> <nobr><span class="hover-cursor-pointer journal-contentLinkColor hover-underline" data-toggle="modal" data-target=".author711177">Kalliopi Tavernaraki</span>,</nobr> <nobr><span class="hover-cursor-pointer journal-contentLinkColor hover-underline" data-toggle="modal" data-target=".author711178">Aikaterini Bougiatioti</span>,</nobr> <nobr><span class="hover-cursor-pointer journal-contentLinkColor hover-underline" data-toggle="modal" data-target=".author711179">Maria Apostolaki</span>,</nobr> <nobr><span class="hover-cursor-pointer journal-contentLinkColor hover-underline" data-toggle="modal" data-target=".author711180">Despina Paraskevopoulou</span>,</nobr> <nobr><span class="hover-cursor-pointer journal-contentLinkColor hover-underline" data-toggle="modal" data-target=".author711181">Alexandra Gogou</span>,</nobr> <nobr><span class="hover-cursor-pointer journal-contentLinkColor hover-underline" data-toggle="modal" data-target=".author711182">Constantine Parinos</span>,</nobr> <nobr><span class="hover-cursor-pointer journal-contentLinkColor hover-underline" data-toggle="modal" data-target=".author711183">Konstantina Oikonomou</span>,</nobr> <nobr><span class="hover-cursor-pointer journal-contentLinkColor hover-underline" data-toggle="modal" data-target=".author711184">Maria Tsagkaraki</span>,</nobr> <nobr><span class="hover-cursor-pointer journal-contentLinkColor hover-underline" data-toggle="modal" data-target=".author711185">Pavlos Zarmpas</span>,</nobr> <nobr><span class="hover-cursor-pointer journal-contentLinkColor hover-underline" data-toggle="modal" data-target=".author711186">Athanasios Nenes<a href="mailto:athanasios.nenes@epfl.ch"><i class="fal fa-envelope ml-1"></i></a></span>,</nobr> <nobr>and <span class="hover-cursor-pointer journal-contentLinkColor hover-underline" data-toggle="modal" data-target=".author711187">Nikolaos Mihalopoulos<a href="mailto:nmihalo@noa.gr"><i class="fal fa-envelope ml-1"></i></a></span></nobr> </div> <div class="modal fade author711175" tabindex="-1" aria-hidden="true"> <div class="modal-dialog modal-dialog-centered modal-dialog-scrollable"> <div class="modal-content"> <div class="modal-header"> <div class="container-fluid p-0"> <h3 class="modal-title">Irini Tsiodra</h3> <div class="row no-gutters"> <div class="col-12"> <a class="orcid-authors-logo" target="_blank" href="https://orcid.org/0000-0001-5392-8986" data-title="https://orcid.org/0000-0001-5392-8986"><svg class="mr-2" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"><image xlink:href="https://www.atmospheric-chemistry-and-physics.net/orcid_icon.svg" src="https://www.atmospheric-chemistry-and-physics.net/orcid_icon_128x128.png" width="100%" height="100%"></image></svg>https://orcid.org/0000-0001-5392-8986</a> </div> </div> </div> <button type="button" class="close" data-dismiss="modal" aria-label="Close"> <span aria-hidden="true">×</span> </button> </div> <div class="modal-body"> <div class="container-fluid p-0"> <div class="row"> <div class="col-12 mb-3"> Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, Heraklion, 71003, Greece </div> </div> <div class="row"> <div class="col-12 mb-3"> Center for the Study of Air Quality and Climate Change, Institute of Chemical Engineering Sciences, Foundation for Research and Technology Hellas, Patras, 26504, Greece </div> </div> </div> </div> </div> </div> </div> <div class="modal fade author711176" tabindex="-1" aria-hidden="true"> <div class="modal-dialog modal-dialog-centered modal-dialog-scrollable"> <div class="modal-content"> <div class="modal-header"> <div class="container-fluid p-0"> <h3 class="modal-title">Georgios Grivas</h3> </div> <button type="button" class="close" data-dismiss="modal" aria-label="Close"> <span aria-hidden="true">×</span> </button> </div> <div class="modal-body"> <div class="container-fluid p-0"> <div class="row"> <div class="col-12 mb-3"> Institute for Environmental Research and Sustainable Development, National Observatory of Athens, Lofos Koufou, Palea Penteli, Athens, 15236, Greece </div> </div> </div> </div> </div> </div> </div> <div class="modal fade author711177" tabindex="-1" aria-hidden="true"> <div class="modal-dialog modal-dialog-centered modal-dialog-scrollable"> <div class="modal-content"> <div class="modal-header"> <div class="container-fluid p-0"> <h3 class="modal-title">Kalliopi Tavernaraki</h3> </div> <button type="button" class="close" data-dismiss="modal" aria-label="Close"> <span aria-hidden="true">×</span> </button> </div> <div class="modal-body"> <div class="container-fluid p-0"> <div class="row"> <div class="col-12 mb-3"> Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, Heraklion, 71003, Greece </div> </div> </div> </div> </div> </div> </div> <div class="modal fade author711178" tabindex="-1" aria-hidden="true"> <div class="modal-dialog modal-dialog-centered modal-dialog-scrollable"> <div class="modal-content"> <div class="modal-header"> <div class="container-fluid p-0"> <h3 class="modal-title">Aikaterini Bougiatioti</h3> </div> <button type="button" class="close" data-dismiss="modal" aria-label="Close"> <span aria-hidden="true">×</span> </button> </div> <div class="modal-body"> <div class="container-fluid p-0"> <div class="row"> <div class="col-12 mb-3"> Institute for Environmental Research and Sustainable Development, National Observatory of Athens, Lofos Koufou, Palea Penteli, Athens, 15236, Greece </div> </div> </div> </div> </div> </div> </div> <div class="modal fade author711179" tabindex="-1" aria-hidden="true"> <div class="modal-dialog modal-dialog-centered modal-dialog-scrollable"> <div class="modal-content"> <div class="modal-header"> <div class="container-fluid p-0"> <h3 class="modal-title">Maria Apostolaki</h3> </div> <button type="button" class="close" data-dismiss="modal" aria-label="Close"> <span aria-hidden="true">×</span> </button> </div> <div class="modal-body"> <div class="container-fluid p-0"> <div class="row"> <div class="col-12 mb-3"> Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, Heraklion, 71003, Greece </div> </div> </div> </div> </div> </div> </div> <div class="modal fade author711180" tabindex="-1" aria-hidden="true"> <div class="modal-dialog modal-dialog-centered modal-dialog-scrollable"> <div class="modal-content"> <div class="modal-header"> <div class="container-fluid p-0"> <h3 class="modal-title">Despina Paraskevopoulou</h3> <div class="row no-gutters"> <div class="col-12"> <a class="orcid-authors-logo" target="_blank" href="https://orcid.org/0000-0002-8482-4925" data-title="https://orcid.org/0000-0002-8482-4925"><svg class="mr-2" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"><image xlink:href="https://www.atmospheric-chemistry-and-physics.net/orcid_icon.svg" src="https://www.atmospheric-chemistry-and-physics.net/orcid_icon_128x128.png" width="100%" height="100%"></image></svg>https://orcid.org/0000-0002-8482-4925</a> </div> </div> </div> <button type="button" class="close" data-dismiss="modal" aria-label="Close"> <span aria-hidden="true">×</span> </button> </div> <div class="modal-body"> <div class="container-fluid p-0"> <div class="row"> <div class="col-12 mb-3"> Institute for Environmental Research and Sustainable Development, National Observatory of Athens, Lofos Koufou, Palea Penteli, Athens, 15236, Greece </div> </div> <div class="row"> <div class="col-12 mb-3"> Center for the Study of Air Quality and Climate Change, Institute of Chemical Engineering Sciences, Foundation for Research and Technology Hellas, Patras, 26504, Greece </div> </div> </div> </div> </div> </div> </div> <div class="modal fade author711181" tabindex="-1" aria-hidden="true"> <div class="modal-dialog modal-dialog-centered modal-dialog-scrollable"> <div class="modal-content"> <div class="modal-header"> <div class="container-fluid p-0"> <h3 class="modal-title">Alexandra Gogou</h3> <div class="row no-gutters"> <div class="col-12"> <a class="orcid-authors-logo" target="_blank" href="https://orcid.org/0000-0001-7327-9223" data-title="https://orcid.org/0000-0001-7327-9223"><svg class="mr-2" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"><image xlink:href="https://www.atmospheric-chemistry-and-physics.net/orcid_icon.svg" src="https://www.atmospheric-chemistry-and-physics.net/orcid_icon_128x128.png" width="100%" height="100%"></image></svg>https://orcid.org/0000-0001-7327-9223</a> </div> </div> </div> <button type="button" class="close" data-dismiss="modal" aria-label="Close"> <span aria-hidden="true">×</span> </button> </div> <div class="modal-body"> <div class="container-fluid p-0"> <div class="row"> <div class="col-12 mb-3"> Institute of Oceanography, Hellenic Centre for Marine Research, Anavyssos, 19013, Greece </div> </div> </div> </div> </div> </div> </div> <div class="modal fade author711182" tabindex="-1" aria-hidden="true"> <div class="modal-dialog modal-dialog-centered modal-dialog-scrollable"> <div class="modal-content"> <div class="modal-header"> <div class="container-fluid p-0"> <h3 class="modal-title">Constantine Parinos</h3> </div> <button type="button" class="close" data-dismiss="modal" aria-label="Close"> <span aria-hidden="true">×</span> </button> </div> <div class="modal-body"> <div class="container-fluid p-0"> <div class="row"> <div class="col-12 mb-3"> Institute of Oceanography, Hellenic Centre for Marine Research, Anavyssos, 19013, Greece </div> </div> </div> </div> </div> </div> </div> <div class="modal fade author711183" tabindex="-1" aria-hidden="true"> <div class="modal-dialog modal-dialog-centered modal-dialog-scrollable"> <div class="modal-content"> <div class="modal-header"> <div class="container-fluid p-0"> <h3 class="modal-title">Konstantina Oikonomou</h3> </div> <button type="button" class="close" data-dismiss="modal" aria-label="Close"> <span aria-hidden="true">×</span> </button> </div> <div class="modal-body"> <div class="container-fluid p-0"> <div class="row"> <div class="col-12 mb-3"> CARE-C Research Center, The Cyprus Institute, Nicosia 2121, Cyprus </div> </div> </div> </div> </div> </div> </div> <div class="modal fade author711184" tabindex="-1" aria-hidden="true"> <div class="modal-dialog modal-dialog-centered modal-dialog-scrollable"> <div class="modal-content"> <div class="modal-header"> <div class="container-fluid p-0"> <h3 class="modal-title">Maria Tsagkaraki</h3> </div> <button type="button" class="close" data-dismiss="modal" aria-label="Close"> <span aria-hidden="true">×</span> </button> </div> <div class="modal-body"> <div class="container-fluid p-0"> <div class="row"> <div class="col-12 mb-3"> Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, Heraklion, 71003, Greece </div> </div> </div> </div> </div> </div> </div> <div class="modal fade author711185" tabindex="-1" aria-hidden="true"> <div class="modal-dialog modal-dialog-centered modal-dialog-scrollable"> <div class="modal-content"> <div class="modal-header"> <div class="container-fluid p-0"> <h3 class="modal-title">Pavlos Zarmpas</h3> </div> <button type="button" class="close" data-dismiss="modal" aria-label="Close"> <span aria-hidden="true">×</span> </button> </div> <div class="modal-body"> <div class="container-fluid p-0"> <div class="row"> <div class="col-12 mb-3"> Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, Heraklion, 71003, Greece </div> </div> </div> </div> </div> </div> </div> <div class="modal fade author711186" tabindex="-1" aria-hidden="true"> <div class="modal-dialog modal-dialog-centered modal-dialog-scrollable"> <div class="modal-content"> <div class="modal-header"> <div class="container-fluid p-0"> <h3 class="modal-title">Athanasios Nenes</h3> <div class="row no-gutters"> <div class="col-12">CORRESPONDING AUTHOR</div> <div class="col-12"><a href="mailto:athanasios.nenes@epfl.ch"><i class="fal fa-envelope mr-2"></i>athanasios.nenes@epfl.ch</a></div> </div> <div class="row no-gutters"> <div class="col-12"> <a class="orcid-authors-logo" target="_blank" href="https://orcid.org/0000-0003-3873-9970" data-title="https://orcid.org/0000-0003-3873-9970"><svg class="mr-2" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"><image xlink:href="https://www.atmospheric-chemistry-and-physics.net/orcid_icon.svg" src="https://www.atmospheric-chemistry-and-physics.net/orcid_icon_128x128.png" width="100%" height="100%"></image></svg>https://orcid.org/0000-0003-3873-9970</a> </div> </div> </div> <button type="button" class="close" data-dismiss="modal" aria-label="Close"> <span aria-hidden="true">×</span> </button> </div> <div class="modal-body"> <div class="container-fluid p-0"> <div class="row"> <div class="col-12 mb-3"> Center for the Study of Air Quality and Climate Change, Institute of Chemical Engineering Sciences, Foundation for Research and Technology Hellas, Patras, 26504, Greece </div> </div> <div class="row"> <div class="col-12 mb-3"> Laboratory of Atmospheric Processes and their Impacts, School of Architecture, Civil & Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, 1015, Switzerland </div> </div> </div> </div> </div> </div> </div> <div class="modal fade author711187" tabindex="-1" aria-hidden="true"> <div class="modal-dialog modal-dialog-centered modal-dialog-scrollable"> <div class="modal-content"> <div class="modal-header"> <div class="container-fluid p-0"> <h3 class="modal-title">Nikolaos Mihalopoulos</h3> <div class="row no-gutters"> <div class="col-12">CORRESPONDING AUTHOR</div> <div class="col-12"><a href="mailto:nmihalo@noa.gr"><i class="fal fa-envelope mr-2"></i>nmihalo@noa.gr</a></div> </div> </div> <button type="button" class="close" data-dismiss="modal" aria-label="Close"> <span aria-hidden="true">×</span> </button> </div> <div class="modal-body"> <div class="container-fluid p-0"> <div class="row"> <div class="col-12 mb-3"> Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, Heraklion, 71003, Greece </div> </div> <div class="row"> <div class="col-12 mb-3"> Institute for Environmental Research and Sustainable Development, National Observatory of Athens, Lofos Koufou, Palea Penteli, Athens, 15236, Greece </div> </div> </div> </div> </div> </div> </div> <div class="abstract sec" id="abstract"><div class="grid-container no-margin header-element"><span class="grid-100 mobile-grid-100 tablet-grid-100 grid-parent more-less-mobile" data-show="#abstract .co-arrow-open,.abstract-content" data-hide="#abstract .co-arrow-closed,.abstract-mobile-bottom-border"><div class="h1"><span class="section-number"> </span>Abstract<span class="hide-on-desktop hide-on-tablet triangleWrapper"> <i class="co-arrow-closed" style="display:none"></i><i class="co-arrow-open" style="display:inline-block"></i></span></div></span></div> <div class="abstract-content show-no-js"><p id="d1e229">Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants in fine particulate matter (PM) long known to have mutagenic and carcinogenic effects, but much is unknown about the importance of local and remote sources for PAH levels observed in population-dense urban environments. A year-long sampling campaign in Athens, Greece, where more than 150 samples were analyzed for 31 PAHs and a wide range of chemical markers, was combined with positive matrix factorization (PMF) to constrain the temporal variability, sources, and carcinogenic risk associated with PAHs. It was found that biomass burning (BB), a source mostly present during wintertime intense pollution events (observed for 18 <span class="inline-formula">%</span> of measurement days in 2017), led to wintertime PAH levels that were 7 times higher than in other seasons and was as important for annual mean PAH concentrations (31 <span class="inline-formula">%</span>) as diesel and oil (33 <span class="inline-formula">%</span>) and gasoline (29 <span class="inline-formula">%</span>) sources. The contribution of non-local sources, although limited on an annual basis (7 <span class="inline-formula">%</span>), increased during summer, becoming comparable to that of local sources combined. The fraction of PAHs (12 members that were included in the PMF analysis) that was associated with BB was also linked to increased health risk compared to the other sources, accounting for almost half the annual PAH carcinogenic potential (43 <span class="inline-formula">%</span>). This can result in a large number of excess cancer cases due to BB-related high PM levels and urges immediate action to reduce residential BB emissions in urban areas facing similar issues.</p></div><span class="abstract-mobile-bottom-border mobile-bottom-border hide-on-desktop hide-on-tablet" style="display:none"></span></div> <div id="oldMobileDownloadBox" class="widget dark-border hide-on-desktop download-and-links"> <div class="legend journal-contentLinkColor">Download & links</div> <div class="content"> <ul class="additional_info no-bullets no-styling"> <li> <a class="triangle" data-toggle=".box-notice" data-duration="300" title="PDF Version (2306 KB)" href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021.pdf" > Article (PDF, 2306 KB) </a> </li> </ul> </div> <div class="content"> <ul class="additional_info no-bullets"> <li> <a class="triangle" href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-supplement.pdf">Supplement</a> <nobr>(1304 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src="https://www.atmospheric-chemistry-and-physics.net/linkedin.png" alt="LinkedIn"> </a> </div> <div class="col pr-0 mobile-native-share"> <a href="#" data-title="Atmospheric Chemistry and Physics" data-text="*Annual exposure to polycyclic aromatic hydrocarbons in urban environments linked to wintertime wood-burning episodes* Irini Tsiodra et al." data-url="https://acp.copernicus.org/articles/21/17865/2021/" class="mobile-native-share share-one-line last"><i class="co-mobile-share display-none"></i></a> </div> </div> </div> <div id="citation-footer" class="sec"> <div class="h1-special journal-contentHeaderColor">How to cite. </div> <div class="citation-footer-content show-no-js"> <p> <div class="citation-footer"> Tsiodra, I., Grivas, G., Tavernaraki, K., Bougiatioti, A., Apostolaki, M., Paraskevopoulou, D., Gogou, A., Parinos, C., Oikonomou, K., Tsagkaraki, M., Zarmpas, P., Nenes, A., and Mihalopoulos, N.: Annual exposure to polycyclic aromatic hydrocarbons in urban environments linked to wintertime wood-burning episodes, Atmos. Chem. Phys., 21, 17865–17883, https://doi.org/10.5194/acp-21-17865-2021, 2021. </div> </p> </div> </div> <div id="article-dates" class="sec"> <div class="article-dates dates-content my-3"> <nobr>Received: 10 May 2021</nobr> – <nobr>Discussion started: 12 May 2021</nobr> – <nobr>Revised: 20 Sep 2021</nobr> – <nobr>Accepted: 21 Sep 2021</nobr> – <nobr>Published: 07 Dec 2021</nobr> </div> </div> <div class="sec intro" id="section1"><div class="grid-container no-margin header-element"><span class="grid-100 mobile-grid-100 tablet-grid-100 grid-parent more-less-mobile" data-hide="#section1 .co-arrow-open,.section1-content" data-show="#section1 .co-arrow-closed,.section1-mobile-bottom-border"><div id="Ch1.S1" class="h1"><span class="label">1</span> Introduction<span class="hide-on-desktop hide-on-tablet triangleWrapper"> <i class="co-arrow-closed"></i><i class="co-arrow-open" style="display:none"></i></span></div></span></div> <div class="section1-content show-no-js hide-on-mobile-soft"><p id="d1e290">Polycyclic aromatic hydrocarbons (PAHs) are abundant in the atmosphere and can be present in the gas or particle phase (Finlayson-Pitts, 1997; Lin et al., 2015). Ambient PAHs originate mainly from internal combustion engines, stationary sources such as power and industrial plants, residential heating (including biomass burning), cooking, and wildfires (Finlayson-Pitts, 1997; Simoneit, 2002; Bond et al., 2013). Several PAHs are characterized as potential carcinogens and/or mutagens (IARC, 2010; Nowakowski et al., 2017). The IARC Group 1 carcinogen benzo[<span class="inline-formula"><i>a</i></span>]pyrene (BaP) is extensively studied among PAHs and is used as a marker for PAH toxicity. The European Union has set an air quality standard for the carcinogenic risk of PAHs with the directive 2004/107/EC. While the directive highlights the necessity of measurement for several PAHs (at least six other members), it lays down an annual target value only for BaP (1 <span class="inline-formula">ng m<sup>−3</sup></span>),<span id="page17866"></span> which is selected as a marker for the carcinogenic risk of polycyclic aromatic hydrocarbons in ambient air.</p><p id="d1e317">The presence of PAHs tends to be highly enhanced in urban environments (Jiang et al., 2014; Mo et al., 2019; Ringuet et al., 2012), such as Athens, Greece. Studies to date in Athens show that PAH concentrations are significantly enhanced during the cold period of the year (Mantis et al., 2005) and linked to a multitude of incomplete combustion sources. Fireplace and woodstove usage for domestic heating in Greece has increased dramatically since the 2010 financial crisis, having considerable impacts on air quality in major urban centers such as Athens (Paraskevopoulou et al., 2014; Grivas et al., 2018; Theodosi et al., 2018) and Thessaloniki (Saffari et al., 2013), which host half the population of Greece.</p><p id="d1e320">It is worth noting that since 2013 several violations of the EU limit value for BaP have been recorded in Greek cities, with concentrations showing a clear wintertime enhancement (NAPMN, 2020). Greek urban centers are not unique in this regard, as residential biomass burning (BB) is a major issue for urban air quality throughout Europe. Studies in central European cities have reported BB contributions to cumulative particle PAH concentrations that even exceed 50 <span class="inline-formula">%</span> (Li et al., 2018; Masiol et al., 2020; Schnelle-Kreis et al., 2007), while in other Mediterranean urban areas its impact appears less profound (Callén et al., 2014).</p><p id="d1e331">Uncontrolled residential BB emissions can lead to the appearance of intense pollution events (IPEs), during which very high urban levels of organic aerosols are observed in urban centers worldwide (Florou et al., 2017; Saffari et al., 2013; Fountoukis et al., 2016). Excessive exposure of urban populations to ambient woodsmoke pollution can cause severe health effects (Kocbach Bølling et al., 2009; Naeher et al., 2007; Wong et al., 2019), especially in view of the very high concentrations of highly oxidized organic species from nighttime chemistry and their potential to enhance toxicity (Kodros et al., 2020).</p><p id="d1e335">Moreover, the contribution of wildfires to regional background PAHs can be significant, given their increased incidence as a result of climate change (McCarty et al., 2020; O'Dell et al., 2020). Wildfires near urban centers can have especially direct and pronounced effects on population exposure. Every summer since 2017, for example, intense episodes of air quality degradation from wildfire smoke near major Greek urban regions (such as Athens, Patras, Heraklion, Kalamata, and Pyrgos) have been recorded. During these events, heavily increased <span class="inline-formula">PM<sub>2.5</sub></span> and <span class="inline-formula">PM<sub>10</sub></span> levels (reaching a few hundreds micrograms per cubic meter) that persist for several days (<span class="uri"><a href="https://panacea-ri.gr" target="_blank">https://panacea-ri.gr</a></span>, last access: 3 November 2021; Amiridis et al., 2012; Stavroulas et al., 2019) are observed.</p><p id="d1e363">Although much work has been done on PAH sources, their attribution using atmospheric samples is often pursued through highly uncertain diagnostic ratios for measured concentrations (Katsoyiannis et al., 2011). Relatively few studies exist in Europe and North America that utilize receptor modeling (e.g., Schnelle-Kreis et al., 2007; Sofowote et al., 2008; Iakovides et al., 2021a), an approach that can quantify the relative contributions of distinct local and regional sources to PAH levels and associated carcinogenic risks that urban populations are exposed to.</p><p id="d1e366">The present study aims to characterize the variability and sources of PAHs in Athens, Greece, one of the largest urban centers in the eastern Mediterranean. This is one of the first studies in Greece and southeastern Europe to utilize positive matrix factorization (PMF) receptor modeling for source apportionment of PAHs. For this, filter-based analysis is combined with online chemical speciation, allowing for the association of PAH groups with specific organic aerosol (OA) components and the verification of PMF-resolved sources. At present, there are only a few studies involving PAHs that comparatively assess offline and online organic aerosol source apportionment (e.g., Bozzetti et al., 2017; Srivastava et al., 2018). To specifically characterize the diurnal variability of PAHs and the BB source, separate daytime and nighttime filter samples were analyzed here, as done in a some previous studies in Greece (Saffari et al., 2013; Tsapakis and Stephanou, 2007). The separation of diesel and gasoline aerosol sources that is attempted in this work is also highly important for Athens, which stands out as a particularity among European cities, given the very small proportion of diesel cars in the passenger fleet due to the ban that existed up to 2011. The resulting identification of carbonaceous aerosol source profiles can provide useful reference for source apportionment studies that use long-term chemical speciation data in urban areas, thus enabling a source-specific toxicity assessment that considers local against regional contributions and is highly important for policies on PAH exposure reduction.</p></div><span class="section1-mobile-bottom-border mobile-bottom-border hide-on-desktop hide-on-tablet"></span></div> <div class="sec" id="section2"><div class="grid-container no-margin header-element"><span class="grid-100 mobile-grid-100 tablet-grid-100 grid-parent more-less-mobile" data-hide="#section2 .co-arrow-open,.section2-content" data-show="#section2 .co-arrow-closed,.section2-mobile-bottom-border"><div id="Ch1.S2" class="h1"><span class="label">2</span> Materials and methods<span class="hide-on-desktop hide-on-tablet triangleWrapper"> <i class="co-arrow-closed"></i><i class="co-arrow-open" style="display:none"></i></span></div></span></div> <div class="section2-content show-no-js hide-on-mobile-soft"><div class="sec"><h2 id="Ch1.S2.SS1"><span class="label">2.1</span> Study area</h2> <p id="d1e384">The Greater Athens Area (GAA, Fig. S1 in the Supplement), with 3.8 million inhabitants, is one of the largest metropolitan regions in southern Europe and a major commercial and transportation hub. Nearly 3 million private cars are registered for circulation in the GAA, along with 0.3 million trucks and buses (Hellenic Statistical Authority, 2020). Up to 2011, diesel-powered private cars were banned in Athens and, even though nowadays they comprise the majority of new sales, they only account for about 10 <span class="inline-formula">%</span> of the fleet. Up to 2011, heating oil was the predominantly used fuel for domestic heating in Athens (in 76 <span class="inline-formula">%</span> of residences). However, its consumption in the GAA decreased by 61 <span class="inline-formula">%</span> in 2011–2018 (Hellenic Statistical Authority, 2019), with people resorting to alternative heating sources, including biomass burning in<span id="page17867"></span> fireplaces and stoves. Industrial activity in the GAA is minor in the central basin as it is mostly concentrated in the Thriassion plain, 10–20 <span class="inline-formula">km</span> to the northwest and separated by a low-altitude mountain range. The port of Piraeus to the southwest is the largest passenger port in Europe and also one of the busiest container ports in the Mediterranean (Fig. S1). The complex topography of the basin favors the appearance of mesoscale flows throughout the year and the frequent stagnation of air masses (Kassomenos et al., 1998).</p> </div><div class="sec"><h2 id="Ch1.S2.SS2"><span class="label">2.2</span> Sampling and analyses</h2> <p id="d1e427">Ambient <span class="inline-formula">PM<sub>2.5</sub></span> samples were collected between 4 December 2016–31 January 2018, at the urban background site of the National Observatory of Athens (NOA) at Thissio (37.97326<span class="inline-formula"><sup>∘</sup></span> N, 23.71836<span class="inline-formula"><sup>∘</sup></span> E), which is located 146 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M19" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">m</mi><mspace width="0.125em" linebreak="nobreak"></mspace><mi mathvariant="normal">a</mi><mo>.</mo><mi mathvariant="normal">s</mi><mo>.</mo><mi mathvariant="normal">l</mi><mo>.</mo></mrow></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="36pt" height="10pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="ea311051787cf155da73f63bfd49f678"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00001.svg" width="100%" height="10pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00001.png"></image></svg></span></span> and is representative of the urban background conditions in central Athens (Stavroulas et al., 2019; Theodosi et al., 2018).</p> <p id="d1e480">During the non-winter months, two samples per week were analyzed on alternating days between weeks. As such, a representative distribution between weekday and weekend samples (69 %–31 %) was achieved, since it is known that this is an important temporal scale inducing variability in urban PAH levels (Dutton et al., 2010; Lough et al., 2006). The same approach was followed for the winter period, focusing at the same time on as many daytime–nighttime pairs as possible to characterize the diurnal patterns. From December to February, separate daytime and nighttime filters were collected every 12 <span class="inline-formula">h</span> (06:00–18:00 LST and 18:00–06:00 LST, respectively) for a total of 80 samples, while 76 total 24 <span class="inline-formula">h</span> filters were sampled from March to November. The sampling schedule also satisfies the 2004/107/EC directive requirements for PAHs (roughly one measurement per week, equally distributed around the year), allowing the comparison with the BaP target value.</p> <p id="d1e499">A low-volume sampler (3.1 PNS 15, Comde Derenda GmbH, Stahnsdorf, DE) with a flow rate of 2.3 <span class="inline-formula">m<sup>3</sup> h<sup>−1</sup></span> was used to collect particles onto quartz-fiber filters of 47 <span class="inline-formula">mm</span> diameter (Flex Tissuquartz, Pall Corporation, Port Washington, NY, USA). The inlet height was 2 <span class="inline-formula">m</span> above ground. Field and laboratory blanks were routinely collected. PAHs in the filter samples were quantified by gas chromatography–mass spectrometry (GC-MS, Agilent 6890N, Agilent Technologies Inc., Santa Clara, CA, USA). Prior to the analysis, samples were spiked with a mixture of deuterated internal standards for identification of PAHs and calculation of recovery efficiencies (16 members, LGC Standards, Middlesex, UK). Extraction was performed following the pre-established procedure of Gogou et al. (1998) with modifications (Parinos et al., 2019) (Sect. S1, Table S1 in the Supplement). Briefly, extracts were obtained using a <span class="inline-formula">50:50</span> <span class="inline-formula"><i>n</i></span>-hexane/dichloromethane mixture and were purified on a silica column. PAHs were eluted with a 10 <span class="inline-formula">mL</span> <span class="inline-formula"><i>n</i></span>-hexane/ethyl acetate (<span class="inline-formula">9:1</span> <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M30" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi>v</mi><mo>/</mo><mi>v</mi></mrow></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="20pt" height="14pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="9667cb19823b351c1e6da855008486d6"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00002.svg" width="100%" height="14pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00002.png"></image></svg></span></span>) mixture and placed into a glass vial for further concentration under a gentle nitrogen stream. [<span class="inline-formula"><sup>2</sup>H<sub>12</sub></span>]perylene, used as an internal standard, was spiked into the vial before sealing and storage. Limits of detection (LODs) were calculated as 3 times the standard deviation of blanks. On the day of the analysis, injections with internal standards were also run to calculate relative response factors (RRFs). The identification of compounds was based on retention time, mass fractionation, and co-injection of standard mixtures.</p> <p id="d1e612">Organic and elemental carbon (OC, EC) were determined by the thermal-optical transmission (TOT) method, using a Sunset carbon analyzer (Sunset Laboratory Inc., Portland, OR, USA) (Cavalli et al., 2010; Paraskevopoulou et al., 2014). Water-soluble ions were detected by ion chromatography (IC) (Paraskevopoulou et al., 2014) and monosaccharide anhydrides (levoglucosan, mannosan, and galactosan) by high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) (Iinuma et al., 2009).</p> <p id="d1e616">The submicrometer organic aerosol (OA) fraction was monitored at the same site by an Aerosol Chemical Speciation Monitor (ACSM, Aerodyne Inc., Billerica, MA, USA) (Ng et al., 2011). The ACSM samples ambient air, through a critical orifice to a particle-focusing aerodynamic lens. The particle beam is driven in the detection chamber where non-refractory particles are flash-vaporized at 600 <span class="inline-formula"><sup>∘</sup>C</span> and ionized by electron impact. Finally, the resulting fragment ions are characterized by a quadrupole mass spectrometer. The obtained organic mass spectra are decomposed into OA components representative of specific sources and processes (namely hydrocarbon-like OA, biomass burning OA, cooking OA, and semi-volatile and low-volatility oxygenated OA), through PMF, based on the multilinear engine ME-2 algorithm, and using the Source Finder toolkit (SoFi) (Canonaco et al., 2013; Bougiatioti et al., 2014). The standard sampling duration of the Q-ACSM that was used is 30 <span class="inline-formula">min</span>. ACSM monitoring was carried out for the majority of the filter-sampling period (December 2016 to January 2018). Data on OA, ionic composition, and organic spectra were available with the exception of September and October 2017. Validated, PMF-resolved OA source contributions were available during December 2016–July 2017. Additional details on the OA measurement and analysis can be found in Stavroulas et al., (2019).</p> <p id="d1e639">Equivalent black carbon (BC) levels were monitored by a seven-wavelength aethalometer (AE33, Magee Scientific, Berkeley, CA, USA), with compensation for loading (DualSpot) and multiple scattering effects (Liakakou et al., 2020). The instrument internally applies the two-component aethalometer model (Drinovec et al., 2015; Sandradewi et al., 2008) and provides online estimates of the BB (%) contribution to BC at 880 <span class="inline-formula">nm</span>, using the assumption that absorbing aerosols from fossil fuel (FF) combustion and BB have distinct spectral properties.</p> <p id="d1e650"><span id="page17868"></span>Regulatory pollutants and meteorological parameters (temperature, wind speed and direction) were routinely measured at Thissio. Reference-grade instrumentation was used for measurement of CO (NDIR, APMA 360, Horiba Inc.), NO<span class="inline-formula"><sub><i>x</i></sub></span> (chemiluminescence, APNA 360, Horiba Inc.), and <span class="inline-formula">O<sub>3</sub></span> (UV-Vis, 49-i, Thermo Fisher Scientific Inc.). NO<span class="inline-formula"><sub><i>x</i></sub></span> concentration data were also obtained from a nearby regulatory (Greek Ministry of Environment and Energy) traffic site (Athinas Str., 0.9 <span class="inline-formula">km</span> NE of Thissio). ACSM, aethalometer, gaseous pollutant, temperature, and wind speed data were averaged on an hourly basis.</p> <p id="d1e690">The 4 d air mass back trajectories, arriving at Thissio at 1000 <span class="inline-formula">m</span> (Grivas et al., 2018; Kalkavouras et al., 2020; Stavroulas et al., 2019), were calculated using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model (Draxler and Rolph, 2016) and grouped daily using cluster analysis (Kalkavouras et al., 2020). The altitude of 1000 <span class="inline-formula">m</span> was chosen to capture the regional transport with a high probability of affecting pollution within the boundary layer (hence, air quality and population exposure) and is consistent with typical planetary boundary layer estimates over Athens (Kokkalis et al., 2020).</p> </div><div class="sec"><h2 id="Ch1.S2.SS3"><span class="label">2.3</span> Source apportionment</h2> <p id="d1e717">PMF analysis was performed using the EPA PMF 5.0 model (Norris et al., 2014). The 12 <span class="inline-formula">h</span> samples collected during the winter intensive campaigns were appropriately combined to 24 <span class="inline-formula">h</span> periods, between 06:00 <span class="inline-formula">LST</span> of each day and 06:00 LST of the following day. This gives 104 total 24 <span class="inline-formula">h</span> samples considered for the analysis. The carbonaceous aerosol speciation dataset that was used consisted of OC, EC, PAHs, oxalate, and levoglucosan. Total carbon (TC, i.e., the sum of OC and EC) was included as a total variable in the PMF model, for a meaningful mass balance approach (Piletic et al., 2013; Valotto et al., 2017). In total, 16 species were entered in the analysis, including 12 PAH members. Rotational and random errors were assessed using the bootstrap (BS) and displacement (DISP) error estimation methods included in the EPA PMF 5.0 software (Paatero et al., 2014). Details on PMF model design parameters, solution metrics, uncertainties, and error indices are provided in the Supplement (Sect. S2, Table S2).</p> </div><div class="sec"><h2 id="Ch1.S2.SS4"><span class="label">2.4</span> PAH contribution to carcinogenic risk</h2> <p id="d1e760">The “toxic equivalence factor” (TEF) approach was used to estimate the carcinogenic potency of measured PAHs, in which the toxicity of each member is expressed using BaP as reference (Taghvaee et al., 2018a): </p><div class="disp-formula" content-type="numbered" id="Ch1.E1"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M45" display="block" overflow="scroll" dspmath="mathml"><mtable><mlabeledtr><mtd><mtext>(1)</mtext></mtd><mtd><mstyle displaystyle="true" class="stylechange"></mstyle><mrow> <mstyle displaystyle="true" class="stylechange"></mstyle> <mo movablelimits="false">∑</mo> <msub> <mtext>BaP</mtext> <mtext>eq</mtext> </msub> <mo>=</mo> <mo movablelimits="false">∑</mo> <mo>(</mo> <msub> <mi>C</mi> <mi>i</mi> </msub> <msub> <mtext>TEF</mtext> <mi>i</mi> </msub> <mo>)</mo> <mo>,</mo> </mrow></mtd></mlabeledtr></mtable></math><div><svg xmlns:svg="http://www.w3.org/2000/svg" width="416pt" height="19pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="fd3441ebffd3ea1d8258273e4b51c70a"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-e_1.svg" width="100%" height="19pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-e_1.png"></image></svg></div></div><p id="d1e760-3"> where <span class="inline-formula"><i>C</i><sub><i>i</i></sub></span> is the concentration (<span class="inline-formula">ng m<sup>−3</sup></span>) and <span class="inline-formula">TEF<sub><i>i</i></sub></span> is the toxicity equivalent factor of each member (Bari et al., 2010; Nisbet and LaGoy, 1992). The lifetime excess cancer risk (ECR) from inhalation was estimated as follows: </p><div class="disp-formula" content-type="numbered" id="Ch1.E2"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M49" display="block" overflow="scroll" dspmath="mathml"><mtable><mlabeledtr><mtd><mtext>(2)</mtext></mtd><mtd><mstyle displaystyle="true" class="stylechange"></mstyle><mrow> <mstyle class="stylechange" displaystyle="true"></mstyle> <mtext>ECR</mtext> <mo>=</mo> <mo movablelimits="false">∑</mo> <msub> <mtext>BaP</mtext> <mtext>eq</mtext> </msub> <msub> <mtext>UR</mtext> <mtext>BaP</mtext> </msub> <mo>,</mo> </mrow></mtd></mlabeledtr></mtable></math><div><svg xmlns:svg="http://www.w3.org/2000/svg" width="416pt" height="19pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="583d10693e972a3b56e945ad411878ad"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-e_2.svg" width="100%" height="19pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-e_2.png"></image></svg></div></div><p id="d1e760-5"> where <span class="inline-formula">UR<sub>BaP</sub></span> (unit risk) refers to the number of excess cancer cases in the population with chronic inhalation exposure to 1 <span class="inline-formula">ng m<sup>−3</sup></span> of BaP over a lifetime of 70 years. Estimations were made using reference <span class="inline-formula">UR<sub>BaP</sub></span> values of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M53" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">1.1</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">6</mn></mrow></msup></mrow></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="51pt" height="14pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="5934f6fe7895665b1eb334aedd8a7eef"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00003.svg" width="100%" height="14pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00003.png"></image></svg></span></span> (0.11 cases per 100 000 people) – according to the Office of Environmental Health Hazards Assessment (OEHHA) of the California Environmental Protection Agency (CalEPA) – and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M54" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">8.7</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">5</mn></mrow></msup></mrow></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="51pt" height="13pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="1ff14490f318b0a6233a8a7ef6f07b8f"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00004.svg" width="100%" height="13pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00004.png"></image></svg></span></span> (8.7 cases per 100 000 people) – according to the World Health Organization (WHO) (Alves et al., 2017; Elzein et al., 2019).</p> </div></div><span class="section2-mobile-bottom-border mobile-bottom-border hide-on-desktop hide-on-tablet"></span></div> <div class="sec" id="section3"><div class="grid-container no-margin header-element"><span class="grid-100 mobile-grid-100 tablet-grid-100 grid-parent more-less-mobile" data-hide="#section3 .co-arrow-open,.section3-content" data-show="#section3 .co-arrow-closed,.section3-mobile-bottom-border"><div id="Ch1.S3" class="h1"><span class="label">3</span> Results and discussion<span class="hide-on-desktop hide-on-tablet triangleWrapper"> <i class="co-arrow-closed"></i><i class="co-arrow-open" style="display:none"></i></span></div></span></div> <div class="section3-content show-no-js hide-on-mobile-soft"><div class="sec"><h2 id="Ch1.S3.SS1"><span class="label">3.1</span> Temporal variability</h2> <p id="d1e955">Figure 1 presents the monthly variation of total PAH concentrations, displaying a notable wintertime enhancement as compared to the summer period. Mean <span class="inline-formula">Σ</span>PAH concentrations in winter 2016–2017, spring 2017, summer 2017, autumn 2017 and winter 2017–2018 were <span class="inline-formula">7.0±10.1</span>, <span class="inline-formula">2.5±4.1</span>, <span class="inline-formula">0.9±0.9</span>, <span class="inline-formula">2.2±3.2</span> and <span class="inline-formula">22.3±26.8</span> <span class="inline-formula">ng m<sup>−3</sup></span>, respectively, indicating a clear seasonal cycle. The mean annual (2017) BaP concentration in this study (0.26 <span class="inline-formula">ng m<sup>−3</sup></span>) did not exceed the EU target value, but nevertheless was higher than the WHO reference level (0.12 <span class="inline-formula">ng m<sup>−3</sup></span>). Largely increased BaP levels were observed during wintertime episodic events. These results can be placed in context by comparison against past studies for PAHs in the GAA (Table S3 in the Supplement) that identified similar seasonal profiles, although not with such pronounced winter-summer differences. Moreover, this study reports the highest mean annual BaP concentrations at a background location in the GAA in over two decades (Marino et al., 2000). In the few studies in the area that have compared traffic with background sites, there appears to be an important roadside enhancement of PAH levels (Andreou and Rapsomanikis, 2009; Mantis et al., 2005; Pateraki et al., 2019). Therefore, it is noteworthy that the present, urban background, BaP annual mean concentration is comparable to the mean BaP concentrations reported at 21 sites in the GAA by a study of annual duration in 2010–2011, 7 of which were high-traffic locations. Specifically, the street-site concentrations were reportedly higher by 44 % and 55 % for <span class="inline-formula">Σ</span>PAHs and BaP, respectively, compared to urban background sites (Jedynska et al., 2014). This comparison likely indicates an increase of urban background levels in Athens, with implications for the population's exposure.</p> <div class="fig" id="Ch1.F1"><a target="_blank" class="figure-link" href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f01-web.png"><img alt="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f01" data-webversion="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f01-web.png" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f01-thumb.png" data-printversion="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f01-high-res.png" data-width="2067" data-height="967"></a><div class="caption"><p id="d1e1086"><strong class="caption-number">Figure 1</strong>The color bars represent the mean monthly concentrations of high (HMW), medium (MHW), and low (LMW) molecular weight PAHs, between December 2016 and January 2018. The pie charts in the lower row show the concentration fractions of LMW, MMW, and HMW PAHs in each seasonin each season, starting with winter on the far left, moving to spring, then to summer in the middle, autumn, and lastly winter again on the far right.</p></div><p class="downloads"><a class="triangle journal-contentLinkColor figure-download" href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f01-high-res.png" target="_blank">Download</a></p></div> <p id="d1e1095">The classification of PAHs by molecular weight is thought to provide information about their sources. For example, low molecular weight PAHs (LMW; 128–178 <span class="inline-formula">g mol<sup>−1</sup></span>) and medium molecular weight PAHs (MMW; 202–228 <span class="inline-formula">g mol<sup>−1</sup></span>) have been linked to diesel engine emissions (Zheng et al.,<span id="page17869"></span> 2017), while MMW and high molecular weight (HMW; 252–300 <span class="inline-formula">g mol<sup>−1</sup></span>) PAH concentrations can be influenced by BB emissions (Han et al., 2019; Masiol et al., 2020). Figure 1 also displays the <span class="inline-formula">Σ</span>PAH fractions of LMW, MMW, and HMW PAHs by season. During winter and autumn, HMW PAHs comprised the most abundant fraction (60 <span class="inline-formula">%</span> and 51 <span class="inline-formula">%</span>, respectively), implying a possible impact from BB. In spring there was an increase of the LMW fraction (49 <span class="inline-formula">%</span>), while during summer, when regional fine aerosol sources maximize their influence (Grivas et al., 2018), the higher percentage (53 <span class="inline-formula">%</span>) came from MMW species.</p> <p id="d1e1190">A prior study carried out during 2001–2002 (Table S3), well before the economic recession in Greece, at a GAA site not adjacent to a major road (Mantis et al., 2005), reported an LMW–MMW–HMW PAH fractionation similar to the present study (Fig. S2 in the Supplement), despite the considerably higher residential BB emissions here. However, the present concentrations of <span class="inline-formula">Σ</span>PAHs and BaP were higher by a factor of 1.4 and 1.8, respectively. This most likely suggests a significant effect of the new BB source on an annual level, since PAH emissions from the road transport sector in Greece remained relatively comparable between the two periods (EIONET, 2021). These results indicate that approaches based on molecular weight (MW) alone have limitations, since many PAH members are emitted by both fossil fuel and biomass burning, and the attribution of PAH sources should be addressed through receptor modeling.</p> <p id="d1e1200">The seasonal variability seen in Fig. 1 is assessed statistically (<span class="inline-formula"><i>t</i></span> tests) to identify significant seasonal differences (winter against non-winter measurements), with results presented in Table S4 in the Supplement. Higher mean PAH concentrations were observed during wintertime, when emissions from processes like biomass burning are more intense. Lower PAH levels were recorded during the non-winter period due to the additional effects of volatilization, photochemical degradation, and enhanced atmospheric dispersion. For all PAH members, concentrations were significantly higher during the winter season at the 0.95 confidence level with the exception of <span class="inline-formula">Σ</span> C1-202 (which instead registered a large number of below detection limit (BDL) values).</p> <p id="d1e1217">Temperature-dependent processes like gas and particle partitioning can affect the observed seasonal variability of semi-volatile PAH compounds. Previous studies in Greece (Iakovides et al., 2021b; Mandalakis et al., 2002; Sitaras and Siskos, 2001, 2008; Terzi and Samara, 2004; Vasilakos et al., 2007) that performed both gas- and particle-phase measurements reported that LMW PAHs were found predominantly in the gas phase (gas-phase fractions: 88 %–97 %), MMW PAHs in both gas and particle phase (gas phase: 46 %–90 %), and HMW PAHs mainly in the particle phase (particle phase: 71 %–100 %). In the present study, only the particle phase of PAHs was measured. In an effort to assess the fractionation of PAH members between the particle phase (measured) and the gas phase in the dataset, an approximation was performed, based on the partitioning theory of semi-volatile organics due to absorption by organic material in the particle phase (Pankow, 1994). This approach and the partitioning–absorption equations used to calculate the partitioning coefficient <span class="inline-formula"><i>K</i><sub>p</sub></span>, and therefore the gas<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M77" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="cacb21262661f636062925dc69bda89d"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00005.svg" width="100%" height="14pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00005.png"></image></svg></span></span>particle concentration ratios, have been used by numerous PAH studies (e.g.,<span id="page17870"></span> Andreou and Rapsomanikis, 2009; Xie et al., 2013). The estimations here were found to be in agreement with the above-mentioned studies in Athens and indicate that volatilization leads to minimal fractions of particle LMW PAHs (found in the gas phase in mean fractions of 71 %–100 %). Regarding MMW, fluoranthene (Flt) and pyrene (Pyr) are the main compounds affected by volatilization (15 %–25 %). HMW members remain relatively unaffected, being partitioned in the particle phase in fractions of 91 %–100 %, even though during regional transport and through successive dilutions a substantial part of HMW could end up being lost from the particle phase due to physical volatilization. The partitioning characterization methodology and results are presented in Sect. S3 of the Supplement (Fig. S3). Finally, as it has been proposed, some organic components can adopt an amorphous solid or semisolid state that can further impact the rate of heterogeneous reactions and multiphase processes (Shiraiwa et al., 2011). In our study for PAHs this does not seem to be the case, as PAHs from outside the region of Athens will be shown later in the paper to be present at low levels.</p> <p id="d1e1238">Apart from volatilization processes, the temporal variability of emission sources can account for a major part of observed seasonal differences. Correlations of PAHs with primary (NO<span class="inline-formula"><sub><i>x</i></sub></span>, CO) and secondary (<span class="inline-formula">O<sub>3</sub></span>) pollutants can provide insights into the related sources and atmospheric processes. The correlation analysis was performed separately for winter and non-winter months, and results are presented in Sect. S3 of the Supplement (Table S5). LMW members, Flt, and Pyr showed weak correlations with primary pollutants (NO<span class="inline-formula"><sub><i>x</i></sub></span>, CO) that were slightly higher during the cold period. MMW and HMW members were highly correlated with CO at Thissio and NO<span class="inline-formula"><sub><i>x</i></sub></span> at the traffic site during both the winter and non-winter periods. For those members, the highest wintertime correlations (<span class="inline-formula"><i>r</i></span>: 0.62–0.88, <span class="inline-formula"><i>p</i><0.01</span>) signify the additional contribution of biomass burning and heating oil combustion emissions that co-emit heavier PAHs, CO, and NO<span class="inline-formula"><sub><i>x</i></sub></span>. In the non-winter period there were relatively high correlations of coronene (Cor), indeno[1,2,3-cd]pyrene (IP), and benzo[ghi]perylene (BghiP) with CO and NO<span class="inline-formula"><sub><i>x</i></sub></span> as measured at Thissio (<span class="inline-formula"><i>r</i></span>: 0.55–0.81, <span class="inline-formula"><i>p</i><0.01</span>) that probably indicate an impact from light-duty vehicles (Weiss et al., 2011) in the absence of domestic burning.</p> </div><div class="sec"><h2 id="Ch1.S3.SS2"><span class="label">3.2</span> Investigating intense pollution events: nighttime vs. daytime</h2> <p id="d1e1344">Summary statistics for 12 and 24 <span class="inline-formula">h</span> <span class="inline-formula">Σ</span>PAH averages are provided in Table 1. The highest PAH concentrations were observed during intense pollution events (IPEs), which in this work are defined as periods with mean BC concentrations exceeding 2 <span class="inline-formula">µg m<sup>−3</sup></span>, and stagnant conditions with wind speeds below 3 <span class="inline-formula">ms<sup>−1</sup></span> and a lack of precipitation (Fourtziou et al., 2017). Peak wintertime levels of BC (Fig. S4 in the Supplement) coincided with BC<span class="inline-formula"><sub>bb</sub></span> maxima, indicating a predominance of biomass burning over other local combustion sources for carbonaceous aerosols during these events (Liakakou et al., 2020). These high levels are considered to be mainly driven by emissions and not changes in mixing-layer height (Liakakou et al., 2020).</p> <span class="tableCitations"></span><div class="table-wrap" id="Ch1.T1"><div class="caption"><p id="d1e1407"><strong class="caption-number">Table 1</strong>Average values <span class="inline-formula">±</span> standard deviation of PAH concentrations categorized according to their molecular weight during wintertime intense pollution events (IPEs).</p></div><a class="table-link" href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-t01.png" target="_blank"><img src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-t01-thumb.png" target="_blank" data-webversion="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-t01-web.png" data-width="2067" data-height="655" data-printversion="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-t01.png" data-csvversion="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-t01.xlsx"></a><p class="downloads"><a class="triangle journal-contentLinkColor table-download" href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-t01.png" target="_blank">Download Print Version</a><span class="hide-on-mobile download-separator"> | </span><a class="triangle journal-contentLinkColor table-download" href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-t01.xlsx" target="_blank">Download XLSX</a></p></div> <p id="d1e1977">Among the 80 winter samples, 50 met the above criteria for IPE (20 daytime and 30 nighttime samples). IPEs occurred with higher frequency during the second winter (24 vs. 17 in the common months: December–January), due to more intense emissions (e.g., the BC mean concentration was 2.6 times higher during the second winter) and reduced atmospheric dispersion (average wind speeds of 3.0 and 1.9 <span class="inline-formula">m s<sup>−1</sup></span> in the first and second winter periods, respectively).</p> <p id="d1e1998">During IPEs, <span class="inline-formula">Σ</span>PAH concentrations displayed a strong night–day gradient, owing to the effect of nighttime residential BB emissions. Several studies have examined the diurnal variability of PAH levels worldwide (e.g., Yan et al., 2009). Similarly pronounced nighttime enhancements have been mostly reported for megacities in East Asia, such as Beijing and Nanjing (Elzein et al., 2019; Haque et al., 2019), where PAH levels are considerably higher than in Athens, due to the intensity and diversity of local sources that include burning of biomass, coal, and plastics. During non-IPE periods, <span class="inline-formula">Σ</span>PAH levels were lower by 43 <span class="inline-formula">%</span> in daytime and 90 <span class="inline-formula">%</span> in nighttime, resulting in daytime levels being higher than nighttime and indicative of substantial contributions from other combustion sources like vehicular traffic.</p> <p id="d1e2031">HMW PAHs had the highest contribution to <span class="inline-formula">Σ</span>PAHs during IPEs and presented the most pronounced day–night differences. MMW PAHs were more abundant during nighttime, with 24 <span class="inline-formula">h</span> levels more than double during IPEs. Levels of LMW PAHs were higher during daytime in both IPE and non-IPE periods, suggesting that biomass burning had a more limited effect in their particle-phase concentrations compared to the higher MW members.</p> <p id="d1e2049">To explore the various sources that drive the variability of PAHs, the correlations of <span class="inline-formula">Σ</span>PAHs with source-specific tracers were examined (Table S6 in the Supplement). Given the very high correlations of <span class="inline-formula">Σ</span>PAHs with BaP (Fig. S5 in the Supplement), especially during nighttime IPEs (<span class="inline-formula"><i>r</i>=0.95</span>, <span class="inline-formula"><i>p</i><0.01</span>), similar associations with examined tracers can be expected for the corresponding PAH carcinogenicity. Strong correlations with biomass burning tracers such as non-sea salt K<span class="inline-formula"><sup>+</sup></span> and BC<span class="inline-formula"><sub>bb</sub></span> were observed, particularly during IPE nights (<span class="inline-formula"><i>r</i></span>: 0.81 and 0.95, respectively, <span class="inline-formula"><i>p</i><0.01</span>). Similarly, levoglucosan, mannosan, and galactosan displayed very high correlations with <span class="inline-formula">Σ</span>PAHs during nighttime IPEs (<span class="inline-formula"><i>r</i></span>: 0.90–0.93, <span class="inline-formula"><i>p</i><0.01</span>). Comparisons were also made with the “fingerprint” ACSM <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M146" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi>m</mi><mo>/</mo><mi>z</mi></mrow></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="42adec4fa6bb3677db555503255b68c2"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00006.svg" width="100%" height="14pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00006.png"></image></svg></span></span> 60 and 73 that are linked to dissociation of levoglucosan produced as a pyrolytic product of biomass (Alfarra et al., 2007; Heringa et al., 2011; Weimer et al., 2008). In fact, filter-based levoglucosan measurements correlated excellently with <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M147" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi>m</mi><mo>/</mo><mi>z</mi></mrow></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="24826ec84731a28530d81d10e0fc5953"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00007.svg" width="100%" height="14pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00007.png"></image></svg></span></span> 60 and 73 ACSM fragments (<span class="inline-formula"><i>r</i>=0.98</span> and 0.97, respectively, <span class="inline-formula"><i>p</i><0.01</span>). <span class="inline-formula">Σ</span>PAHs exhibited strong correlations with <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M151" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi>m</mi><mo>/</mo><mi>z</mi></mrow></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="c395e69edea76caa7d2b902fc2baa6cb"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00008.svg" width="100%" height="14pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00008.png"></image></svg></span></span> 60 and 73 during nighttime IPEs, with <span class="inline-formula"><i>r</i></span> values of 0.88 and 0.86 (<span class="inline-formula"><i>p</i><0.01</span>), respectively,<span id="page17871"></span> indicating the impact of BB emissions. A close association was also observed between <span class="inline-formula">Σ</span>PAHs and submicrometer organic aerosol (OA). During the period when PMF-resolved ACSM OA components were available, the strongest correlations were observed with biomass burning organic aerosol (BBOA) and semi-volatile oxygenated organic aerosol (SV-OOA), the components that for the cold period in Athens correspond to fresh and processed BB organic aerosol, respectively (Stavroulas et al., 2019). On the contrary, <span class="inline-formula">Σ</span>PAHs were uncorrelated with low-volatility oxygenated organic aerosol (LV-OOA), which mostly represents OA of regional origin. An absence of correlation between <span class="inline-formula">Σ</span>PAHs and highly oxidized OA from ACSM data has been also reported by field and experimental studies (Cui et al., 2020; Zheng et al., 2020).</p> <p id="d1e2263">The results indicate a significant impact of BB emissions on PAH levels during nighttime IPEs. The ratio of <span class="inline-formula">Σ</span>PAHs to levoglucosan during these events was 53 <span class="inline-formula">%</span> lower than in daytime, when biomass burning and therefore levoglucosan concentrations decrease. This indicates the important effects of additional PAH sources such as vehicular traffic, a finding consistent with past studies in Greece (Saffari et al., 2013). The levoglucosan/(mannosan <span class="inline-formula">+</span> galactosan) ratio can also indicate whether solid fuels used for heating are either “aged” (e.g., aged wood or lignite) producing more levoglucosan or more “fresh” (Saffari et al., 2013). The calculated value close to 6 for both daytime and nighttime samples suggests that solid fuels used for residential heating in Athens are mainly associated with fresh firewood and that their type has not changed since 2013, when a similar wintertime ratio was reported in Athens (Fourtziou et al., 2017). Finally, the ratio of levoglucosan to mannosan can be indicative of wood type, with hardwood use (e.g., olive, oak, beech) producing ratios around 14–15, while softwood (e.g., pine) burning leads to lower ratios, around 4 (Schmidl et al., 2008). In the present study, the levoglucosan<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M160" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="7ae9d62930fc9a75f7435a1e921c6226"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00009.svg" width="100%" height="14pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00009.png"></image></svg></span></span>mannosan ratio ranged from 7.3 to 9.7 (Table S7 in the Supplement), indicating a balanced use of both wood types, in agreement with observations at the same site during the 2013–2014 winter (Fourtziou et al., 2017), once again supporting that a mixture of fresh softwood and hardwood is consistently used for residential heating over the recent years.</p> </div><div class="sec"><h2 id="Ch1.S3.SS3"><span class="label">3.3</span> PMF modeling and source characterization</h2> <p id="d1e2303">Solutions with three to eight factors were examined, with the four-factor solution deemed as the most physically meaningful (a detailed presentation of the selected solution can be found in Sect. S5 of the Supplement). The four identified factors are presented below; a more extensive discussion on their validation is provided in Sect. S5 of the Supplement.</p> <div class="fig" id="Ch1.F2"><a target="_blank" class="figure-link" href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f02-web.png"><img alt="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f02" data-webversion="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f02-web.png" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f02-thumb.png" data-printversion="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f02-high-res.png" data-width="2067" data-height="1260"></a><div class="caption"><p id="d1e2308"><strong class="caption-number">Figure 2</strong>Percentage contributions of individual sources to mean modeled concentrations of PAHs and other carbonaceous species obtained from PMF analysis for 24 <span class="inline-formula">h</span> samples collected at Thissio, Athens, during December 2016–January 2018.</p></div><p class="downloads"><a class="triangle journal-contentLinkColor figure-download" href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f02-high-res.png" target="_blank">Download</a></p></div> <p id="d1e2325">The first factor was attributed to biomass burning (BB). Levoglucosan, a well-established BB signature marker, is almost exclusively associated with this factor (Fig. 2). The factor is also characterized by important loadings in 5–6-ring PAHs, a feature that has been reported in BB source profiles of PMF studies in urban areas worldwide (Han et al., 2019; Masiol et al., 2020; Taghvaee et al., 2018b). The strong presence of BaP in the factor is consistent with results from studies in European cities (Li et al., 2018; Srivastava et al., 2018) and also with a recent study at Thissio (Fourtziou et al., 2017) that reported direct associations between wintertime BaP levels and several BB tracers. The OC<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M162" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="13ce93c86819e9fbd9087669649b4443"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00010.svg" width="100%" height="14pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00010.png"></image></svg></span></span>EC ratio in the profile was 4.2, higher than the other local sources and characteristic of fresh BB emissions. It was also comparable to the value (3.7) calculated for the BB source at the same site by a long-term <span class="inline-formula">PM<sub>2.5</sub></span> source apportionment study (Theodosi et al., 2018). Moreover, the source contributions registered the highest correlations, among the four factors, with BB external tracers and specifically with BC<span class="inline-formula"><sub>bb</sub></span> (<span class="inline-formula"><i>r</i>=0.93</span>, <span class="inline-formula"><i>p</i><0.01</span>) and water-soluble K<span class="inline-formula"><sup>+</sup></span> (<span class="inline-formula"><i>r</i>=0.61</span>, <span class="inline-formula"><i>p</i><0.01</span>). Similarly, the strongest correlations were observed between the BB source and the <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M170" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi>m</mi><mo>/</mo><mi>z</mi></mrow></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="389f15c212cfcd6c0cd89bbd414c28c7"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00011.svg" width="100%" height="14pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00011.png"></image></svg></span></span> 60 and 73 ACSM fragments (<span class="inline-formula"><i>r</i>=0.88</span> and 0.86, respectively, <span class="inline-formula"><i>p</i><0.01</span>), further validating its identification. The biomass burning source was closely related to the BBOA component (<span class="inline-formula"><i>r</i>=0.85</span>, <span class="inline-formula"><i>p</i><0.01</span>) with a slope of 0.003 indicating that the 12 members included in the PMF analysis comprise about 0.3 <span class="inline-formula">%</span> of BBOA (Poulain et al., 2011). Similar associations have been reported by studies comparing OA components from online aerosol mass spectrometry and source contributions from offline filter-based<span id="page17872"></span> source apportionment (Bozzetti et al., 2017; Srivastava et al., 2021). The bivariate polar wind plot (calculated according to the methodology of Uria-Tellaetxe and Carslaw, 2014) for contributions of the BB source (Fig. S6a in the Supplement) indicates the local character of the source, with concentrations being enhanced during low-wind conditions, as it has been observed at the same site for fresh BB aerosols emitted in central Athens (Kaskaoutis et al., 2021; Stavroulas et al., 2019). The factor was present almost exclusively during the winter months (Fig. S7 in the Supplement), when local wood-burning emissions for residential heating intensify, leading to frequent IPE.</p> <p id="d1e2483">The second factor was linked to gasoline-powered vehicles, which constitute the major fraction (over 90 <span class="inline-formula">%</span>) of the vehicular fleet in the GAA. The factor was characterized by stronger contributions to HMW PAHs (e.g., IP, BghiP, and Cor) over LMW members (Fig. 2). This feature has been used to differentiate the gasoline source from general traffic sources in several PAH source apportionment studies (Callén et al., 2013; Javed et al., 2019; Sofowote et al., 2008; Wu et al., 2014). The OC<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M177" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="8134d4143174f8de4294978158979f1c"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00012.svg" width="100%" height="14pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00012.png"></image></svg></span></span>EC ratio in the source profile was 1.9, within the range (1.7–2.3) typically reported for fresh emissions from gasoline vehicles (Grivas et al., 2012). The source contribution time series presented the highest correlations with BC<span class="inline-formula"><sub>ff</sub></span> (<span class="inline-formula"><i>r</i>=0.79</span>, <span class="inline-formula"><i>p</i><0.01</span>), which is mostly a proxy of traffic emissions impacting Thissio (Liakakou et al., 2020). It was the only factor that correlated significantly during both non-winter (<span class="inline-formula"><i>r</i>=0.80</span>, <span class="inline-formula"><i>p</i><0.01</span>) and winter (<span class="inline-formula"><i>r</i>=0.66</span>, <span class="inline-formula"><i>p</i><0.01</span>) periods with CO, which is emitted mainly by gasoline vehicles in the GAA (Fameli and Assimakopoulos, 2016). In contrast, the BB source correlated with CO only in winter (<span class="inline-formula"><i>r</i>=0.83</span>, <span class="inline-formula"><i>p</i><0.01</span>) due to strong CO emissions from wood burning during IPEs (Gratsea et al., 2017). Moreover, this was also the only local source that was correlated (<span class="inline-formula"><i>r</i>=0.57</span>, <span class="inline-formula"><i>p</i><0.01</span>) with ACSM hydrocarbon-like organic aerosol (HOA) during the non-winter months, when HOA is exclusively associated with vehicular traffic (Stavroulas et al., 2019). However, unraveling the HOA contributions from gasoline and diesel vehicles is challenging (Shah et al., 2018), and while some experimental results support a close connection of ambient HOA profiles with gasoline vehicle emissions (Collier et al., 2015), there are field source apportionment studies that report high correlations of HOA with both fuel-type combustion sources (Al-Naiema et al., 2018). The wind plot for the factor contributions (Fig. S6b), given the absence of a strong directional pattern, is again suggestive of aerosols produced in the vicinity of the site (central Athens). Higher contributions were observed during the winter months (Fig. S7), consistent with the increased traffic in the center of Athens (especially during the December holiday period) relative to the vacation months of July–August.</p> <p id="d1e2632">The third factor was associated with emissions from diesel and oil combustion and is characterized by an increased abundance of lower MW members (Shirmohammadi et al., 2016; Zheng et al., 2017). It presented the highest contributions to Flt and Pyr among local sources and also substantial loadings of Benzo[a]anthracene (BaA), Chrysene (Chr), Benzo[b&k] fluoranthene (BbkF), and BaP, along with smaller – compared to the gasoline factor – loadings of IP and BghiP (Fig. 2). Comparable patterns can be observed<span id="page17873"></span> in source profiles of other PMF studies that distinguish diesel and gasoline sources (e.g., Agudelo-Castañeda and Teixeira, 2014; Liu et al., 2019), where contributions in the diesel factor were found relatively increased for 4–5-ring PAHs and decreased for HMW members. The OC<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M189" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="d53d44f98937dfe064857196b33de6fc"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00013.svg" width="100%" height="14pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00013.png"></image></svg></span></span>EC ratio was 1.6, higher than typically reported values for diesel exhaust, which could indicate moderate aging. Higher OC<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M190" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="05524174c9378e1f55a3ee58e5a67a55"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00014.svg" width="100%" height="14pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00014.png"></image></svg></span></span>EC ratios can also be expected in the cases of heavy-duty diesel vehicles in creeping mode (Pio et al., 2011) and non-traffic oil combustion emissions (e.g., ships in the port). Based on its wind plot, the factor, while still local, presents a relative enhancement for moderate-speed winds transporting aerosols from the S–W sectors of the GAA (Fig. S6c). Primary pollution hot spots are found in this direction, such as the port of Piraeus (at a distance of 7–11 <span class="inline-formula">km</span>) and the industrial and commercial hub of the Athens basin (2–4 <span class="inline-formula">km</span>) that is traversed by the E75 international route, the most heavily trafficked – and frequently congested – highway in the GAA (Grivas et al., 2019). Therefore, the area to the SW of the site is characterized by increased circulation of light- and heavy-duty diesel vehicles. As with the gasoline factor, the contribution time series recorded statistically significant (<span class="inline-formula"><i>p</i><0.01</span>) correlations with external combustion indicators, albeit ones that are weaker (<span class="inline-formula"><i>r</i>=0.66</span>, <span class="inline-formula"><i>p</i><0.01</span> with CO; <span class="inline-formula"><i>r</i>=0.39</span>, <span class="inline-formula"><i>p</i><0.01</span> with BC<span class="inline-formula"><sub>ff</sub></span>). Although the factor was uncorrelated with the HOA during the non-winter months, it recorded a large correlation during the first winter period (<span class="inline-formula"><i>r</i>=0.88</span>, <span class="inline-formula"><i>p</i><0.01</span>), potentially signifying a measurable contribution of stationary heating fuel combustion – recognized as an additional contributing factor to HOA during winter in Athens (Stavroulas et al., 2019) – to the diesel factor during stagnation events. It is recognized, however, that this correlation could be inflated by a common boundary layer or a stagnation effect of traffic and residential emissions, and therefore more research is need to confirm the finding. When examining the entire period with availability of OA component data (December 2016–July 2017), it was observed that the source had a consistent association (<span class="inline-formula"><i>r</i>=0.74</span>, <span class="inline-formula"><i>p</i><0.01</span>) with the HOA<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M203" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="8cc825d855110de1cd11ea964f72d0cc"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00015.svg" width="100%" height="14pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00015.png"></image></svg></span></span>CO ratio, which is expected to be higher for aerosols from diesel combustions (Reyes-Villegas et al., 2016).</p> <p id="d1e2791">The fourth factor was characteristic of non-local contributions to carbonaceous aerosol. It was mainly associated with high contributions to OC and EC, which at urban background locations are moderately impacted from local primary sources and mostly driven by aerosols regionally transported to the receptor site (Buzcu-Guven et al., 2007; Hasheminassab et al., 2014). The dominance of regional secondary sources at urban and suburban background sites has been identified by the majority of aerosol source apportionment studies in the GAA (Diapouli et al., 2017; Grivas et al., 2018; Paraskevopoulou et al., 2015; Theodosi et al., 2018) and other urban areas worldwide, such as Mexico City (Aiken et al., 2009) and Paris (Skyllakou et al., 2014). The factor was also characterized by a high contribution of oxalate, an important secondary constituent of water-soluble organic carbon (Myriokefalitakis et al., 2011). The contributions of non-local sources were positively correlated with sulfate and ammonium (<span class="inline-formula"><i>r</i></span>: 0.57 and 0.51, respectively, <span class="inline-formula"><i>p</i><0.01</span>), indicators of regionally transported secondary aerosol. The non-local PMF factor showed the strongest associations with SV-OOA and LV-OOA, the secondary, oxidized OA components (Srivastava et al., 2021; Xu et al., 2021). This was mainly observed during the non-winter months (<span class="inline-formula"><i>r</i>=0.77</span> and 0.55, <span class="inline-formula"><i>p</i><0.01</span>, respectively), while in the winter period the factor was again correlated with LV-OOA of regional origin (<span class="inline-formula"><i>r</i>=0.48</span>, <span class="inline-formula"><i>p</i><0.05</span>) but not with SV-OOA, which in winter is instead associated with the fast processing of heating emissions (Stavroulas et al., 2019). This is the only factor that showed a statistically significant (<span class="inline-formula"><i>p</i><0.01</span>) enhancement (Fig. S7) during the non-winter months, due to increased photo-oxidation for production of secondary organics under stronger insolation. The polar plot of Fig. S6d displays the typically observed (Stavroulas et al., 2019) large dispersion of concentration enhancements along the SW–NE axis of the Athens basin, indicating the association of the factor with transport on a larger-than-urban spatial level. A considerable fraction of Flt and Pyr was attributed to this factor. Studies performed at regional background sites that are mainly impacted by long-range transport have attributed increased contributions of Flt and Pyr to aerosols deriving from distant combustion of coal and heavy oil (Lhotka et al., 2019; Mao et al., 2018; Miura et al., 2019; Wang et al., 2014). The OC<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M211" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="20090b9b43795c74dde704c86435aa57"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00016.svg" width="100%" height="14pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00016.png"></image></svg></span></span>EC ratio in the source profile (2.9) was increased compared to the petroleum-related sources (1.6–1.9), but not as much as usually reported for secondary aerosol factors. Given this, and the fact that PAHs are subject to oxidative aging and removal during atmospheric transport (Galarneau, 2008; Ravindra et al., 2008), it is likely that the non-local factor not only includes transboundary aerosols but also partially aged aerosol from a less extended spatial scale (e.g., from energy production using fossil fuels in continental Greece or from emissions from marine oil combustion in the Aegean Sea). In support of this, it is noted that the centroids of all identified air mass trajectory clusters during the study period converge to the north of the GAA before arriving in the Athens basin (see also the discussion in Sect. 3.4).</p> </div><div class="sec"><h2 id="Ch1.S3.SS4"><span class="label">3.4</span> Source contributions</h2> <p id="d1e2889">Average source contributions to PAHs and TC are presented in Fig. 3 for the calendar year 2017 (January to December; 93 24 <span class="inline-formula">h</span> values) to achieve consistent statistical sampling of each season. The following discussion is focused on the contributions to PAHs, while the contributions to TC are discussed in Sect. S5 of the Supplement. The mean annual contributions of sources to mean modeled OC and EC are displayed in Fig. S8 in the Supplement.</p> <div class="fig" id="Ch1.F3"><a target="_blank" class="figure-link" href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f03-web.png"><img alt="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f03" data-webversion="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f03-web.png" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f03-thumb.png" data-printversion="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f03.png" data-width="2067" data-height="666"></a><div class="caption"><p id="d1e2902"><strong class="caption-number">Figure 3</strong>Fractional contributions of PMF-resolved sources to mean modeled concentrations of <strong>(a)</strong> TC, <strong>(b)</strong> the sum of 12 PAHs included in the PMF analysis, and <strong>(c)</strong> estimated BaP<span class="inline-formula"><sub>eq</sub></span>.</p></div><p class="downloads"><a class="triangle journal-contentLinkColor figure-download" href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f03.png" target="_blank">Download</a></p></div> <p id="d1e2929"><span id="page17874"></span>Regarding local sources, the annual contribution of biomass burning to <span class="inline-formula">Σ</span>PAHs is amplified compared to TC (31 <span class="inline-formula">%</span> vs. 12 <span class="inline-formula">%</span>, Fig. 2a and b) and even more so when assessing only the contributions to carcinogenic PAHs (36 <span class="inline-formula">%</span>, Fig. 3c). The large impact of biomass burning on long- and short-term PAH exposure becomes more evident considering that it is essentially a source active mainly in wintertime and manifests mostly during IPEs (18 <span class="inline-formula">%</span> of measurement days in 2017).</p> <p id="d1e2972">The other two local sources (diesel and/or oil and gasoline) accounted for a combined 62 <span class="inline-formula">%</span> of <span class="inline-formula">Σ</span>PAHs (Fig. 3b), highlighting the importance of urban vehicular emissions on a long-term basis but not during IPEs. Even though the participation of diesel cars is minimal in the passenger fleet in Athens (<span class="inline-formula"><10</span> <span class="inline-formula">%</span>, the vast majority being Euro 5 and 6 vehicles), the contribution of the diesel and oil factor is at least comparable to the gasoline factor for <span class="inline-formula">Σ</span>PAHs (and much larger for TC), indicating that it is probably emissions from older light- and heavy-duty vehicles (and to an extent stationary emissions) that should be associated with the significant contributions of this source. Manoli et al. (2016), reported an even larger gap between diesel and gasoline contributions to <span class="inline-formula">Σ</span>PAHs (51 <span class="inline-formula">%</span> vs. 30 <span class="inline-formula">%</span> approximately) at an urban background location in Thessaloniki, Greece, during 2011–2012. Even before the lifting of the ban on private diesel cars in Athens and Thessaloniki (2011), diesel emissions were considered to be more important regarding the impact of road transport on PAH concentrations (Andreou and Rapsomanikis, 2009; Viras and Siskos, 1993). Comparing with these studies, a declining contribution to PAHs of diesel vehicles in Greek cities is implied.</p> <p id="d1e3039">Non-local sources were the major contributors to total carbon concentrations (65 <span class="inline-formula">%</span>) at the Thissio site (Fig. 3a) – consistent with findings from previous studies at urban background sites in the GAA and elsewhere. The effect of non-local sources is greatly reduced (Fig. 3b) when examining contributions to <span class="inline-formula">Σ</span>PAHs (7 <span class="inline-formula">%</span>) against those of the three local sources (29 <span class="inline-formula">%</span>–33 %). Figure 4a shows that non-local daily contributions remain lower than 20 <span class="inline-formula">%</span> during winter but regularly exceed 50 <span class="inline-formula">%</span> during summer.</p> <div class="fig" id="Ch1.F4"><a target="_blank" class="figure-link" href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f04-web.png"><img alt="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f04" data-webversion="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f04-web.png" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-f04-thumb.png" data-width="2067" data-height="1165"></a><div class="caption"><p id="d1e3092"><strong class="caption-number">Figure 4</strong>The four dominant clusters of backward trajectories, Black Sea (cluster 1: red), eastern Europe (cluster 2: blue), western Europe (cluster 3: purple), and northern Greece/Balkans (cluster 4: brown). Panel <strong>(a)</strong> shows the local and non-local relative source contributions during the study period. Panels <strong>(b, c)</strong> show the non-local contribution to <span class="inline-formula">Σ</span>PAHs concentration according to the respective air mass origin.</p></div><p class="downloads"></p></div> <p id="d1e3114">Non-local contributions are intimately linked with regional transport; therefore, an air mass trajectory cluster analysis can help understand their variability and origins. Four major air mass source regions are identified for the GAA during the study period using 96 <span class="inline-formula">h</span> back trajectories: the Black Sea area (with a frequency of 43 <span class="inline-formula">%</span>), northern Greece/Balkans (32 <span class="inline-formula">%</span>), western Europe (20 <span class="inline-formula">%</span>), and eastern Europe (5 <span class="inline-formula">%</span>).</p> <p id="d1e3157">When examining total PAH levels per trajectory cluster, it should be considered that relevant synoptic circulation patterns can affect the intensity of local emission sources (e.g., during wintertime cold fronts may lead to increased BB), and thus this impedes a fully unbiased assessment. The source apportionment results were utilized here instead to remove the effect of local sources and to associate trajectory clusters more directly with non-local sources.</p> <p id="d1e3161">Figure 4b shows that the non-local contribution of the four clusters to <span class="inline-formula">Σ</span>PAH concentrations during the non-winter period was practically the same (differences from the mean within 10 <span class="inline-formula">%</span>). For the winter period it can be observed that the contribution from eastern Europe was very small compared to the other clusters. During summer (Fig. 4c), the highest contributions were related to trajectories from eastern Europe, an area identified as a hotspot of PAH production in Europe (EEA, 2018; Guerreiro et al., 2016; Rogula-Kozłowska et al., 2013). However, the small frequency (5 <span class="inline-formula">%</span>) of the cluster in summer should be noted. An important summertime enhancement can be also observed for non-local contributions associated with trajectories from the Black Sea area, where extensive summer agricultural burning has been identified as a significant source of carbonaceous aerosol in the eastern Mediterranean (Amiridis et al., 2009; Sciare et al., 2005). This occurrence is mainly for the period from July to September (Sciare et al., 2008) and can be better observed using satellite imagery and fire maps (MODIS, VIIRS-NOAA). Moreover, emission inventories from GWIS (Global Wildfire Information System) verify the identified source area as a major hotspot of fire-related emissions. These fires derive predominantly from agricultural waste burning. For example, in 2017, the fractions of total burned area that were associated with croplands were 96.5 <span class="inline-formula">%</span> and 96.1 <span class="inline-formula">%</span> in Ukraine<span id="page17875"></span> and Turkey, respectively. Relevant information is provided in Sect. S5, Fig. S9 in the Supplement. For the western Europe and northern Greece/Balkan clusters, the mean contributions remained effectively constant on a seasonal basis. In non-winter months, when non-local sources become much more prominent, contributions do not depend on air mass sector, possibly indicating that anthropogenic production of harmful aerosols is a continental-scale problem.</p> </div><div class="sec"><h2 id="Ch1.S3.SS5"><span class="label">3.5</span> Contributions to carcinogenic potency and risk assessment</h2> <p id="d1e3212">The calculated annual BaP<span class="inline-formula"><sub>eq</sub></span> value at the urban background site of Thissio for 2017 was 0.53 <span class="inline-formula">ng m<sup>−3</sup></span>, higher than the one reported during 2013 for a suburban background site in the GAA that is less affected by local emissions (0.3 <span class="inline-formula">ng m<sup>−3</sup></span>) (Alves et al., 2017). With the exception of sites in heavily industrialized areas (Kozielska et al., 2014), studies in other European and North American cities generally calculate BaP<span class="inline-formula"><sub>eq</sub></span> values in the same order of magnitude as in Athens. However, much higher values on the order of several <span class="inline-formula">ng m<sup>−3</sup></span> BaP<span class="inline-formula"><sub>eq</sub></span> are usually reported for cities in China. (Table S8 in the Supplement). Figure S10 in the Supplement shows the members that contribute the most to BaP<span class="inline-formula"><sub>eq</sub></span> during the full measurement period; 50 <span class="inline-formula">%</span> of the annual BaP<span class="inline-formula"><sub>eq</sub></span> is attributed to BaP, consistent with studies worldwide (Amador-Muñoz et al., 2010) and confirming its importance as an indicator of PAH carcinogenic risk. The BaP<span class="inline-formula"><sub>eq</sub></span> value displayed a clear seasonal variability, with the highest levels during winter and the lowest in summer (Table S9 in the Supplement). Especially during nighttime IPE in the winter of 2017–2018, the mean BaP concentration and the BaP<span class="inline-formula"><sub>eq</sub></span> estimate reached peak values of 2.75 and 5.18 <span class="inline-formula">ng m<sup>−3</sup></span>, respectively. Comparing to the mean BaP<span class="inline-formula"><sub>eq</sub></span> from all non-IPE samples (0.21 <span class="inline-formula">ng m<sup>−3</sup></span>), it appears that these short-duration wintertime events disproportionately influence the mean annual BaP<span class="inline-formula"><sub>eq</sub></span> value (0.53 <span class="inline-formula">ng m<sup>−3</sup></span>).</p> <p id="d1e3408">The PMF-resolved concentration profiles were used to obtain BaP<span class="inline-formula"><sub>eq</sub></span> contributions of each source. The annual contributions of biomass burning, diesel and oil, and gasoline to BaP<span class="inline-formula"><sub>eq</sub></span> were 43 <span class="inline-formula">%</span>, 36 <span class="inline-formula">%</span>, and 17 <span class="inline-formula">%</span>, respectively, with the remaining 4 <span class="inline-formula">%</span> attributed to non-local sources (Fig. 3d). These results clearly highlight BB, in spite of its seasonal and highly episodic character, as a principal driver of long-term carcinogenic risk. Moreover, the carcinogenic risk of PAHs should come under appraisal in the setting of wildfires impacting large urban agglomerations in vulnerable areas with increasing frequency, such as California, Australia, and southern Europe. Such events, especially in the summer months when ambient exposure duration is increased, might become an important factor for both short- and long-term health effects in the years ahead. In the few European studies, where BB factors were apportioned and their contributions to BaP<span class="inline-formula"><sub>eq</sub></span> were reported (mainly in southern European cities), these contributions were not that pronounced, even<span id="page17876"></span> during the winter season (Callén et al., 2014; Masiol et al., 2012; Iakovides et al., 2021a).</p> <p id="d1e3471">Inhalation ECR values (Table S9), estimated for the annual period, were equal to <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M267" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">0.58</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">6</mn></mrow></msup></mrow></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="57pt" height="14pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="42a36182b9df969ac8d1013ca2d21b81"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00017.svg" width="100%" height="14pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00017.png"></image></svg></span></span> (OEHHA method) and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M268" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">45.73</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">6</mn></mrow></msup></mrow></math><span><svg xmlns:svg="http://www.w3.org/2000/svg" width="63pt" height="14pt" class="hide-js svg-formula" dspmath="mathimg" md5hash="1c035706fd091291c7ed0c049ec870a2"><image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00018.svg" width="100%" height="14pt" src="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-ie00018.png"></image></svg></span></span> (WHO method). These estimates approached or exceeded 10<span class="inline-formula"><sup>−6</sup></span>, thought to be a threshold above which carcinogenic risks become not acceptable (U.S. EPA, 2011). At current levels, 76 <span class="inline-formula">%</span> of the excess risk would be attributed to wintertime exposure, mostly during IPEs, a percentage largely superior to those corresponding to the other three seasons (4 %–14 %). Based on the stricter WHO unit risk, an excess of 4.6 cancer cases per 100 000 people can be linked to inhalation exposure to PAHs in urban background conditions in Athens. For the 3 million living in the central Athens basin, it can be projected that the number of excess cancer cases could be well over 100.</p> </div></div><span class="section3-mobile-bottom-border mobile-bottom-border hide-on-desktop hide-on-tablet"></span></div> <div class="sec conclusions" id="section4"><div class="grid-container no-margin header-element"><span class="grid-100 mobile-grid-100 tablet-grid-100 grid-parent more-less-mobile" data-hide="#section4 .co-arrow-open,.section4-content" data-show="#section4 .co-arrow-closed,.section4-mobile-bottom-border"><div id="Ch1.S4" class="h1"><span class="label">4</span> Conclusions<span class="hide-on-desktop hide-on-tablet triangleWrapper"> <i class="co-arrow-closed"></i><i class="co-arrow-open" style="display:none"></i></span></div></span></div> <div class="section4-content show-no-js hide-on-mobile-soft"><p id="d1e3539">Domestic biomass burning is identified as a considerable source of carcinogenic PAHs in one of the most populated regions of the Mediterranean. Overutilization of wood burning for domestic heating during the economic recession in Greece persists even today despite the improved economy, leading to a significant increase in annual urban background levels of <span class="inline-formula">Σ</span>PAHs and BaP with respect to the period preceding the recession. The local biomass burning source, which is present almost exclusively during the winter period, emerges as the most important contributor to carcinogenic toxicity of <span class="inline-formula">Σ</span>PAHs (43 <span class="inline-formula">%</span> on an annual basis). Therefore, wintertime exposure is seen as responsible for the largest part (76 <span class="inline-formula">%</span>) of the estimated excess lifetime cancer risk. This large wintertime enhancement (estimated in 2017) can be mostly attributed to a few nighttime episodes (19 events in 105 <span class="inline-formula">d</span> of measurement), revealing a disproportional impact of residential BB emissions but also an opportunity for targeted intervention measures. Given this and the extended usage of biomass burning throughout Europe (e.g., France, Germany, Ireland, and the UK), European action and policies aimed at the regulation of biomass burning emissions are immediately required as they can lead considerable benefits for public health.</p><p id="d1e3580">Sources related to local road transport were found to be responsible for the major part of <span class="inline-formula">Σ</span>PAH concentrations (62 <span class="inline-formula">%</span>), indicating that current EU planning to further curb vehicular emissions and promote electromobility can lead to tangible results in reducing urban aerosol toxicity. However, caution is still needed for non-exhaust emissions that are also linked to enhanced particle toxicity and are expected to emerge as the principal vehicle-related particle source in the years to come (Alves et al., 2018; Daellenbach et al., 2020). In this work, there are some indications that the effects of diesel vehicles are weakening in Greek cities, which is consistent with the modernization of the commercial vehicle fleet over the last 2 decades. More research in other European cities, where diesel penetration in the passenger fleets is much higher, could be rather useful to study the relative contributions and trends of diesel and gasoline vehicle contributions.</p><p id="d1e3598">Non-local sources had a relatively small contribution to <span class="inline-formula">Σ</span>PAH level and toxicity, but their relative contribution during the warm period of the year becomes comparable with that of local sources. It should be noted that photochemistry of PAHs could be an important degradation pathway (mainly in summer) leading to formation of oxidized PAHs products, which can be considerably more toxic than parent PAHs. As this may revise the relative importance of non-local compared to local sources, oxy-PAHs are a subject of ongoing research with measurements at Thissio.</p><p id="d1e3608">It was shown that a comprehensive observation dataset, combined with receptor modeling and back-trajectory analysis provides powerful insights into the source apportionment and contributions to the health risks from PAH exposure. Despite the large body of work to date on PAHs, similar studies are surprisingly scarce in Europe and the US, and thus it is intended that the present study will motivate urgently needed follow-ups in other urban environments.</p></div><span class="section4-mobile-bottom-border mobile-bottom-border hide-on-desktop hide-on-tablet"></span></div> <div id="section5" class="sec"><div class="grid-container no-margin header-element"><span class="grid-100 mobile-grid-100 tablet-grid-100 grid-parent more-less-mobile" data-hide="#section5 .co-arrow-open,.section5-content" data-show="#section5 .co-arrow-closed,.section5-mobile-bottom-border"><div class="h1"><span class="section-number"> </span>Data availability<span class="hide-on-desktop hide-on-tablet triangleWrapper"> <i class="co-arrow-closed"></i><i class="co-arrow-open" style="display:none"></i></span></div></span></div> <div class="section5-content show-no-js hide-on-mobile-soft"><p id="d1e3616">Data are available upon request to the corresponding authors.</p></div><span class="section5-mobile-bottom-border mobile-bottom-border hide-on-desktop hide-on-tablet"></span></div> <div id="section6" class="sec"> <div class="grid-container no-margin header-element"><span class="grid-100 mobile-grid-100 tablet-grid-100 grid-parent more-less-mobile" data-hide="#section6 .co-arrow-open,.section6-content" data-show="#section6 .co-arrow-closed,.section6-mobile-bottom-border"><div class="h1"><span class="section-number"> </span>Supplement<span class="hide-on-desktop hide-on-tablet triangleWrapper"> <i class="co-arrow-closed"></i><i class="co-arrow-open" style="display:none"></i></span></div></span></div> <div class="section6-content show-no-js hide-on-mobile-soft"><p id="d1e3619">The supplement related to this article is available online at: <a href="https://doi.org/10.5194/acp-21-17865-2021-supplement">https://doi.org/10.5194/acp-21-17865-2021-supplement</a>.</p></div><span class="section6-mobile-bottom-border mobile-bottom-border hide-on-desktop hide-on-tablet"></span></div> <div id="section7" class="sec"><div class="grid-container no-margin header-element"><span class="grid-100 mobile-grid-100 tablet-grid-100 grid-parent more-less-mobile" data-hide="#section7 .co-arrow-open,.section7-content" data-show="#section7 .co-arrow-closed,.section7-mobile-bottom-border"><div class="h1"><span class="section-number"> </span>Author contributions<span class="hide-on-desktop hide-on-tablet triangleWrapper"> <i class="co-arrow-closed"></i><i class="co-arrow-open" style="display:none"></i></span></div></span></div> <div class="section7-content show-no-js hide-on-mobile-soft"><p id="d1e3628">Conceptualization was done by AN and NM. The methodology was developed by NM, AN, IT, and GG. The formal analysis was performed by IT and GG. The investigation was undertaken by IT, GG, AB, DP, MA, AG, CP, KT, PZ, MT, and KO. IT and GG prepared the original draft, which was reviewed and edited by IT, GG, AB, DP, NM, and AN. The study was supervised by NM and AN. Funding acquisition and project administration were performed by AN and NM.</p></div><span class="section7-mobile-bottom-border mobile-bottom-border hide-on-desktop hide-on-tablet"></span></div> <div id="section8" class="sec"><div class="grid-container no-margin header-element"><span class="grid-100 mobile-grid-100 tablet-grid-100 grid-parent more-less-mobile" data-hide="#section8 .co-arrow-open,.section8-content" data-show="#section8 .co-arrow-closed,.section8-mobile-bottom-border"><div class="h1"><span class="section-number"> </span>Competing interests<span class="hide-on-desktop hide-on-tablet triangleWrapper"> <i class="co-arrow-closed"></i><i class="co-arrow-open" style="display:none"></i></span></div></span></div> <div class="section8-content show-no-js hide-on-mobile-soft"><p id="d1e3634">The contact author has declared that neither they nor their co-authors have any competing interests.</p></div><span class="section8-mobile-bottom-border mobile-bottom-border hide-on-desktop hide-on-tablet"></span></div> <div id="section9" class="sec"><div class="grid-container no-margin header-element"><span class="grid-100 mobile-grid-100 tablet-grid-100 grid-parent more-less-mobile" data-hide="#section9 .co-arrow-open,.section9-content" data-show="#section9 .co-arrow-closed,.section9-mobile-bottom-border"><div class="h1"><span class="section-number"> </span>Disclaimer<span class="hide-on-desktop hide-on-tablet triangleWrapper"> <i class="co-arrow-closed"></i><i class="co-arrow-open" style="display:none"></i></span></div></span></div> <div class="section9-content show-no-js hide-on-mobile-soft"><p id="d1e3640">Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.</p></div><span class="section9-mobile-bottom-border mobile-bottom-border hide-on-desktop hide-on-tablet"></span></div> <div class="ack sec" id="section10"> <div class="grid-container no-margin header-element"><span class="grid-100 mobile-grid-100 tablet-grid-100 grid-parent more-less-mobile" data-hide="#section10 .co-arrow-open,.section10-content" data-show="#section10 .co-arrow-closed,.section10-mobile-bottom-border"><div class="h1"><span class="section-number"> </span>Acknowledgements<span class="hide-on-desktop hide-on-tablet triangleWrapper"> <i class="co-arrow-closed"></i><i class="co-arrow-open" style="display:none"></i></span></div></span></div> <div class="section10-content show-no-js hide-on-mobile-soft"><p id="d1e3646">This work has been funded by the European Research Council, CoG-2016 project PyroTRACH (726165) H2020-EU.1.1. – Excellent Science. We also acknowledge support by the “PANhellenic infrastructure for Atmospheric Composition and climatE change” (MIS 5021516), which is implemented<span id="page17877"></span> under the Action “Reinforcement of the Research and Innovation Infrastructure”, funded by the Operational Programme “Competitiveness, Entrepreneurship and Innovation” (NSRF 2014–2020) and co-financed by Greece and the European Union (European Regional Development Fund). The authors thank Eleni Liakakou for providing BC and BC speciation data (BC<span class="inline-formula"><sub>ff</sub></span> and BC<span class="inline-formula"><sub>wb</sub></span>) for Thissio, Ioannis Hatzianestis of HCMR for providing guidance in the PAH analysis method, Iasonas Stavroulas for the contribution in the ACSM PMF analysis, Panayiotis Kalkavouras for the trajectory cluster analysis, and Maria Lianou for filter collection.</p></div><span class="section10-mobile-bottom-border mobile-bottom-border hide-on-desktop hide-on-tablet"></span></div> <div id="section11" class="sec"><div class="grid-container no-margin header-element"><span class="grid-100 mobile-grid-100 tablet-grid-100 grid-parent more-less-mobile" data-hide="#section11 .co-arrow-open,.section11-content" data-show="#section11 .co-arrow-closed,.section11-mobile-bottom-border"><div class="h1"><span class="section-number"> </span>Financial support<span class="hide-on-desktop hide-on-tablet triangleWrapper"> <i class="co-arrow-closed"></i><i class="co-arrow-open" style="display:none"></i></span></div></span></div> <div class="section11-content show-no-js hide-on-mobile-soft"><p id="d1e3669">This research has been supported by the H2020 European Research Council (grant no. 726165) and the Hellenic Ministry of Environment and Energy (grant no. MIS 5021516).</p></div><span class="section11-mobile-bottom-border mobile-bottom-border hide-on-desktop hide-on-tablet"></span></div> <div id="section12" class="sec"><div class="grid-container no-margin header-element"><span class="grid-100 mobile-grid-100 tablet-grid-100 grid-parent more-less-mobile" data-hide="#section12 .co-arrow-open,.section12-content" data-show="#section12 .co-arrow-closed,.section12-mobile-bottom-border"><div class="h1"><span class="section-number"> </span>Review statement<span class="hide-on-desktop hide-on-tablet triangleWrapper"> <i class="co-arrow-closed"></i><i class="co-arrow-open" style="display:none"></i></span></div></span></div> <div class="section12-content show-no-js hide-on-mobile-soft"><p id="d1e3675">This paper was edited by Lynn M. Russell and reviewed by two anonymous referees.</p></div><span class="section12-mobile-bottom-border mobile-bottom-border hide-on-desktop hide-on-tablet"></span></div> <div class="ref-list sec" id="section13"> <div class="grid-container no-margin header-element"><span class="grid-100 mobile-grid-100 tablet-grid-100 grid-parent more-less-mobile" data-hide="#section13 .co-arrow-open,.section13-content" data-show="#section13 .co-arrow-closed,.section13-mobile-bottom-border"><div class="h1"><span class="section-number"> </span>References<span class="hide-on-desktop hide-on-tablet triangleWrapper"> <i class="co-arrow-closed"></i><i class="co-arrow-open" style="display:none"></i></span></div></span></div> <div class="section13-content show-no-js hide-on-mobile-soft"><p class="ref" id="bib1.bib1"><span class="mixed-citation">Agudelo-Castañeda, D. M. and Teixeira, E. 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Version" href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021.xml">Full-text XML</a> </li> </ul> </div> <div class="content"> <ul class="additional_info no-bullets no-styling"> <li> <a class="triangle" href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021-supplement.pdf">Supplement</a> <nobr>(1304 KB)</nobr> </li> <li><a class="triangle" href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021.bib">BibTeX</a></li> <li><a class="triangle" href="https://acp.copernicus.org/articles/21/17865/2021/acp-21-17865-2021.ris">EndNote</a></li> </ul> </div> </div> <div class="widget dark-border"> <div class="legend journal-contentLinkColor">Short summary</div> <div class="content hide-js shortSummaryFull">We analyze observations from year-long measurements at Athens, Greece. Nighttime wintertime PAH levels are 4 times higher than daytime, and wintertime values are 15 times higher than summertime. Biomass burning aerosol during wintertime pollution events is responsible for these significant wintertime enhancements and accounts for 43 % of the population exposure to PAH carcinogenic risk. Biomass burning poses additional health risks beyond those associated with the high PM levels that develop.</div> <div style="display: none" class="content show-js shortSummaryShorten">We analyze observations from year-long measurements at Athens, Greece. 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ACP - Annual exposure to polycyclic aromatic hydrocarbons in urban environments linked to wintertime wood-burning episodes