<div>
<h3>Learning Objective</h3>
<ul>
<li>Recall what causes photochemical smog and why it is a problem for humans</li>
</ul>
</div>
<hr/>
<div>
<h3>Key Points</h3>
<ul>
<li>Photochemical smog is composed of primary and secondary pollutants.</li>
<li>Primary pollutants, which include nitrogen oxides and volatile organic compounds, are introduced into the atmosphere via vehicular emissions and industrial processes.</li>
<li>Secondary pollutants, like ozone, result from the reaction of primary pollutants with ultraviolet light.</li>
<li>Photochemical smog is most common in sunny and dry cities, like Los Angeles.</li>
<li>Smog has a variety of negative health impacts.</li>
</ul>
</div>
<hr/>
<h3>Terms</h3>
<ul>
<li><strong>volatile:</strong> evaporating or vaporizing readily under normal conditions; having a low boiling point</li>
<li><strong>monatomic:</strong> a substance consisting of a single atom (not molecules of the element); examples include the <a data-lesson="occurrence-preparation-and-properties-of-the-noble-gases" data-subject="chemistry" data-tutorial="metals-metalloids-nonmetals" href="https://app.ulearngo.com/chemistry/metals-metalloids-nonmetals/occurrence-preparation-and-properties-of-the-noble-gases">noble gases</a> and many metals</li>
<li><strong>Photochemical smog:</strong> a type of air pollution formed through solar <a data-lesson="summarizing-biological-effects-of-radiation" data-subject="chemistry" data-tutorial="nuclear-chemistry" href="https://app.ulearngo.com/chemistry/nuclear-chemistry/summarizing-biological-effects-of-radiation">radiation</a> reacting with airborne pollutants, like nitrogen oxides and volatile organic compounds</li>
</ul>
<hr/>
<p>Photochemical smog is a major contributor to air pollution. The word “smog” was originally coined as a <a data-lesson="mixtures" data-subject="chemistry" data-tutorial="classification-of-matter" href="https://app.ulearngo.com/chemistry/classification-of-matter/mixtures">mixture</a> of “smoke” and “fog” and was historically used to describe air pollution produced from the burning of coal, which released smoke and <a data-lesson="sulfur" data-subject="chemistry" data-tutorial="metals-metalloids-nonmetals" href="https://app.ulearngo.com/chemistry/metals-metalloids-nonmetals/sulfur">sulfur</a> dioxide. Nineteenth and 20th century London was particularly well-known for this type of air pollution. The “Great Smog of 1952” was identified as the cause of over 4,000 deaths in London. While air pollution caused by burning coal has become less common, the <a data-lesson="enthalpy-of-combustion" data-subject="chemistry" data-tutorial="thermochemistry" href="https://app.ulearngo.com/chemistry/thermochemistry/enthalpy-of-combustion">combustion</a> of fossil fuels continues to affect air quality.</p>
<div class="wp-caption alignnone" style="width: 654px"><img alt="The" height="575" src="https://data.ulearngo.com/assets/f8f7924e-5b08-4c5d-b675-6e8c90534a76" width="654"/><p class="wp-caption-text"><b>Smog in London during the 19th and 20th centuries</b>: Claude Monet made several trips to London between 1899 and 1901, during which he painted views of the Thames and Houses of Parliament which show the sun struggling to shine through London’s smog-laden atmosphere.</p></div>
<h2>What Causes Photochemical Smog?</h2>
<p>The components of photochemical smog were established during the 1950s. This type of air pollution is formed through the reaction of solar radiation with airborne pollutants like nitrogen oxides and volatile organic compounds. These compounds, which are called primary pollutants, are often introduced into the atmosphere through automobile emissions and industrial processes. Ultraviolet light can split nitrogen dioxide into nitric oxide and monatomic oxygen; this monatomic <a data-lesson="occurrence-preparation-and-compounds-of-oxygen" data-subject="chemistry" data-tutorial="metals-metalloids-nonmetals" href="https://app.ulearngo.com/chemistry/metals-metalloids-nonmetals/occurrence-preparation-and-compounds-of-oxygen">oxygen</a> can then react with oxygen gas to form ozone. Products like ozone, aldehydes, and peroxyacetyl nitrates are called secondary pollutants. The mixture of these primary and secondary pollutants forms photochemical smog.</p>
<p>Both the primary and secondary pollutants in photochemical smog are highly reactive. These oxidizing compounds have been linked to a variety of negative health outcomes; ozone, for example, is known to irritate the lungs. Smog is a particular health danger in some of the world’s sunniest and most populated cities, such as Los Angeles; Los Angeles is typically sunny, and the sun reacts with the <a data-lesson="hazard-signs" data-subject="chemistry" data-tutorial="chemistry-essential-ideas" href="https://app.ulearngo.com/chemistry/chemistry-essential-ideas/hazard-signs">chemicals</a> produced by cars and other industrial processes. Smog can also affect areas of the country that are sunny less frequently, such as New York City. In fact, most major cities have problems with smog and air pollution.</p>
<div class="wp-caption alignnone" style="width: 659px"><img alt="Smog in New York City: Photochemical smog is composed of primary and secondary pollutants. Primary pollutants include nitrogen oxides and volatile organic compounds as a result of industrial processes, while secondary pollutants are created through the reaction of primary pollutants with ultraviolet light." height="429" src="https://data.ulearngo.com/assets/7b78751d-8f32-43c2-9bb0-0326a867b1ed" width="659"/><p class="wp-caption-text"><b>Smog in New York City</b>: Photochemical smog is composed of primary and secondary pollutants. Primary pollutants include nitrogen oxides and volatile organic compounds as a result of industrial processes, while secondary pollutants are created through the reaction of primary pollutants with ultraviolet light.</p></div>

1da7dde6-444c-4cfc-9055-98f781c809ca

Photochemical Smog

Chemistry generally explores the substances of which matter is composed, the investigation of their properties and reactions, and the use of such reactions to form new substances. 

Chemistry

Discover the industrial production processes for fertilizers and the advantages and disadvantages of inorganic and organic fertilizers, explore the effects of pollutants like CO2, radon, and formaldehyde on indoor air quality and learn about the chemical processes behind natural phenomena like auroras and volcanic activity.


Photochemical Smog

Track Your Learning Progress