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<!DOCTYPE html> <html lang="en"> <head> <title>Photochemical Smog Chemistry Tutorial</title> <meta charset="utf-8">  <meta name="HandheldFriendly" content="True"> <meta name="MobileOptimized" content="500"> <meta name="viewport" content="width=device-width, height=device-height initial-scale=1.0, maximum-scale=5.0, user-scalable=1"> <meta name="keywords" content="photochemical smog, smog, chemistry of photochemical smog, pollution, ozone, nitrogen dioxide, nitric oxide, peroxyacetylnitrate, PAN, peroxyacylnitrate, peroxyacyl nitrate, peroxyacetyl nitrate, catalytic converters, chemistry, science, science education"> <meta name="description" content="Causes of photochemical smog and use of catalytic converters to reduce it, tutorial suitable for chemistry students"> <meta name="author" content="Janice Stubbings"> <link rel="icon" href="https://www.ausetute.com.au/favicon.ico" type="image/x-icon"> <LINK REL="apple-touch-icon" HREF="/apple-touch-icon.png" /> <LINK REL=stylesheet TYPE="text/css" HREF="../style/AUS_style.css"> <script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-6425224463369806" crossorigin="anonymous"></script> </head> <body style="color:white;" onbeforeprint="window.top.location.href='https://www.ausetute.com.au/thief.html'" > <header> <a href="https://www.ausetute.com.au"><IMG SRC="../images/headersm.gif" style="width:300px; height:84px; border:0px;" ALT="go to the AUS-e-TUTE homepage"></a> </header> <nav> <a href="https://www.ausetute.com.au/index.html" ID="navlink">More Free Tutorials</a> <a href="https://www.ausetute.com.au/register.html" ID="navlink">Become a Member</a> <a href="http://www.ausetute.com.au/members/testcent.html" ID="navlink">Members Log&dash;in</a> <a href="https://www.ausetute.com.au/contact.html" ID="navlink">Contact Us</a> <P style="text-align:center;">  <ins class="adsbygoogle" style="display:block" data-ad-client="ca-pub-6425224463369806" data-ad-slot="9327566501" data-ad-format="auto" data-full-width-responsive="true"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script> </P> <P>Want chemistry games, drills, tests and more?</P> <P>You need to become an <a href="https://www.ausetute.com.au/register.html" ID="notes">AUS-e-TUTE Member</a>!</P> </nav> <section> <article> <H1> Photochemical Smog Chemistry Tutorial </H1> <H2>Key Concepts</H2> <P>Photochemical smog is a type of air pollution produced when sunlight acts upon motor vehicle exhaust gases to form harmful substances such as <a href="https://www.ausetute.com.au/cfcozone.html" ID="notes">ozone</a> (O<sub>3</sub>), <a href="https://www.ausetute.com.au/namalkanal.html" ID="notes">aldehydes</a> and peroxyacetylnitrate (PAN). </P> <P>Photochemical smog formation requires the following conditions:</P> <UL><P><LI>a still, sunny day </LI></P> <P><LI>temperature inversion (pollutants accumulate in the lower inversion layer)</LI></P> </UL> <P>Ozone causes breathing difficulties, headaches, fatigue and can aggrevate respiratory problems. </P> <P>The peroxyacetylnitrate (CH<sub>3</sub>CO-OO-NO<sub>2</sub>) in photochemical smog can irritate the eyes, causing them to water and sting. </P> <P style="text-align:center;">  <ins class="adsbygoogle" style="display:block" data-ad-client="ca-pub-6425224463369806" data-ad-slot="9327566501" data-ad-format="auto" data-full-width-responsive="true"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); </script> </P> </article> <article> <P style="color:black; text-align:center;">Please do not block ads on this website. <BR>No ads = no money for us = no free stuff for you!</P> <H2>Ozone Production</H2> <P>Motor vehicles produce exhaust gases containing oxides of nitrogen such as nitrogen dioxide (NO<sub>2</sub>) and nitric oxide (NO). </P> <P>At the high temperatures of the car's combustion chamber (cylinder), nitrogen and oxygen from the air react to form nitric oxide (NO):</P> <P><div id="tbl"><TABLE class="space" BORDER=0 ALIGN=CENTER> <tr><td>N<sub>2</sub>(g) + O<sub>2</sub>(g) → 2NO(g)</td></tr> </TABLE> </div> </P> <P>Some of the nitric oxide (NO) reacts with oxygen to form nitrogen dioxide (NO<sub>2</sub>):</P> <P><div id="tbl"><TABLE class="space" BORDER=0 ALIGN=center> <TR><TD>2NO(g) + O<sub>2</sub>(g) → 2NO<sub>2</sub>(g)</TD></TR> </TABLE> </div> </P> <P>The mixture of nitric oxide (NO) and nitrogen dioxide (NO<sub>2</sub>) is sometimes referred to as NO<sub><I>x</I></sub>. </P> <P>When the nitrogen dioxide (NO<sub>2</sub>) concentration is well above clean air levels and there is plenty of sunlight, then an oxygen atom splits off from the nitrogen dioxide molecule:</P> <P><div id="tbl"><TABLE class="space" BORDER=0 ALIGN=center> <TR><TD>NO<sub>2</sub>(g)<BR></TD> <TD align=center><EM style="font-size:8pt;">sunlight</EM><BR><EM style="font-size:25pt;"> → </EM></TD> <TD>NO(g)</TD> <TD>+</TD> <TD>O(g)</TD></TR> </TABLE> </div> </P> <P>This oxygen atom (O) can react with oxygen molecules (O<sub>2</sub>) in the air to form ozone (O<sub>3</sub>):</P> <P><div id="tbl"><TABLE class="space" BORDER=0 ALIGN=CENTER> <TR><TD>O + O<sub>2</sub> → O<sub>3</sub></TD></TR> </TABLE> </div> </P> <P>Nitric oxide can remove ozone by reacting with it to form nitrogen dioxide (NO<sub>2</sub>) and oxygen (O<sub>2</sub>):</P> <P><div id="tbl"><TABLE class="space" BORDER=0 ALIGN=CENTER> <TR><TD>NO(g) + O<sub>3</sub>(g) → NO<sub>2</sub>(g) + O<sub>2</sub>(g)</TD></TR> </TABLE> </div> </P> <P>When the ratio of NO<sub>2</sub> to NO is greater than 3, the formation of ozone is the dominant reaction. If the ratio is less than 0.3, then the nitric oxide reaction destroys the ozone at about the same rate as it is formed, keeping the ozone concentration below harmful levels. </P> <P>The reaction of <a href="https://www.ausetute.com.au/namsanes.html" ID="notes">hydrocarbons</a> (unburnt petrol) with nitric oxide and oxygen produce nitrogen dioxide also in the presence of sunlight, increasing the ratio of nitrogen dioxide to nitric oxide. </P> <div ID="AUS_box"> <P>Do you know this?</P> <P><a href="https://www.ausetute.com.au/register.html" ID="lnkbutton">Join AUS-e-TUTE!</a> <P>Play the game now!</P> </div> </article> <article> <H2>Peroxyacetylnitrate Production</H2> <P>Nitrogen dioxide (NO<sub>2</sub>), oxygen (O<sub>2</sub>) and hydrocarbons (unburnt petrol) react in the presence of sunlight to produce peroxyacetylnitrate (CH<sub>3</sub>CO-OO-NO<sub>2</sub>): </P> <P><div id="tbl"><TABLE class="space" BORDER=0 ALIGN=CENTER cellpadding=10> <TR><TD>NO<sub>2</sub>(g) + O<sub>2</sub>(g) + hydrocarbons<BR></TD> <TD align=center><EM style="font-size:8pt;">sunlight</EM><BR><EM style="font-size:25pt;"> → </EM></TD> <TD>CH<sub>3</sub>CO-OO-NO<sub>2</sub>(g)</TD></TR> </TABLE> </div> </P> <div ID="AUS_box"> <P>Do you understand this?</P> <P><a href="https://www.ausetute.com.au/register.html" ID="lnkbutton">Join AUS-e-TUTE!</a> <P>Take the test now!</P> </div> </article> <article> <H2>Catalytic Converters</H2> <P>Catalytic converters on motor vehicle exhausts are a way of trying to reduce the carbon monoxide and nitrogen oxide emissions.</P> <P>The <a href="https://www.ausetute.com.au/enerprof.html" ID="notes">catalyst</a> used is either platinum or a combination of platinum and rhodium. </P> <P>The platinum catalyses the reaction of unburnt hydrocarbon (such as pentane) and oxygen (O<sub>2</sub>) to produce carbon dioxide (CO<sub>2</sub>) and water vapour (H<sub>2</sub>O):</P> <P><div id="tbl"><TABLE class="space" BORDER=0 cellpadding=10 ALIGN=CENTER> <TR><TD>C<sub>5</sub>H<sub>12</sub><BR>(pentane)</TD> <TD>+<BR></TD> <TD>8O<sub>2</sub><BR></TD> <TD align=center><EM style="font-size:8pt;">platinum catalyst</EM><BR><EM style="font-size:30pt;"> → </EM></TD> <TD>5CO<sub>2</sub><BR></TD> <TD>+<BR></TD> <TD>6H<sub>2</sub>O<BR></TD></TR> </TABLE> </div> </P> <P>The rhodium catalyses the reaction of carbon monoxide (CO) and nitric oxide (NO) to form carbon dioxide (CO<sub>2</sub>) and nitrogen gas (N<sub>2</sub>):</P> <P><div id="tbl"><TABLE class="space" BORDER=0 cellpadding=10 ALIGN=CENTER> <TR><TD>2CO + 2NO<BR></TD> <TD align=center><EM style="font-size:8pt;">rhodium catalyst</EM><BR><EM style="font-size:30pt;"> → </EM></TD> <TD>2CO<sub>2</sub> + N<sub>2</sub></TD></TR> </TABLE> </div> </P> <P>The reduction of nitric oxide (NO) to nitrogen gas (N<sub>2</sub>) must proceed more quickly than the oxidation of carbon monoxide (CO) to carbon dioxide (CO<sub>2</sub>) or else all the carbon monoxide will be oxidised to carbon dioxide before it can be used to reduce the nitric oxide. </P> <P>Motor vehicles can only use catalytic converters if they use unleaded petrol since the lead in petrol renders the catalyst inactive. </P> <div ID="AUS_box"> <P>Can you apply this?</P> <P><a href="https://www.ausetute.com.au/register.html" ID="lnkbutton">Join AUS-e-TUTE!</a></P> <P>Take the exam now!</P> </div> </article> </section> <aside> <P style="text-align:center;"> <div id="gads" style="text-align:center;">  <ins class="adsbygoogle" style="display:block" data-ad-client="ca-pub-6425224463369806" data-ad-slot="9327566501" data-ad-format="auto" data-full-width-responsive="true"></ins> <script> (adsbygoogle = window.adsbygoogle || []).push({}); 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