Photochemical smog refers to smog produced when sunlight interacts with molecules of harmful chemicals and pollutants in the Earth's atmosphere. Photochemical smog classifies as air pollution. It exists in areas around the world, and concentrates primarily in the thick airs above cities and major metropolitan regions.
Although similar, photochemical smog distinguishes itself from regular smog in several ways. Regular smog develops through the interaction between smoke and fog. This smog also occurs in larger concentrations in cities and densely populated areas. However, it lacks the chemical component necessary for development of photochemical smog.
Several different chemicals combine during the process of photochemical smog formation. The chemicals comprising this type of air pollution include nitrogen oxide, Volatile Organic Compounds (VOCs), ozone and a synthetic substance called PAN. These chemicals enter the atmosphere from different sources.
Nitrogen oxide leaches into the air in the exhaust emissions of trucks and cars. Burning gasoline produces this synthetic compound, which rises into the atmosphere. Car and truck fuel also produce VOCs. However, VOCs also escape into the air from paint products and pesticides.
Photochemical smog develops from excessive amounts of ozone, which is a type of synthetic oxygen. PAN molecules, also synthetic compounds, form with the interaction of other synthetic compounds in the air.