Definition - What does Photochemical Smog mean?
Photochemical smog refers to a type of air pollution that is generated when the sun's ultraviolet rays react with nitrogen oxides in the Earth's atmosphere. Regions that experience higher levels of photochemical smog also observe higher corrosion rates in metallic structures that are situated outdoors.
Corrosionpedia explains Photochemical Smog
Photochemical smog is typically visible as a brown haze in the sky. It is most prominent during moments of sunlight in densely populated, warm cities. Certain cities, such as Los Angeles, Beijing, Sydney and Mexico City are known for their significant rates of photochemical smog.
Photochemical smog generates increased rates of corrosion in exposed metals because it tends to trap particulate matter, chemicals and ozone in the metal's immediate environment. These compounds then react with the metal substrate or penetrate to form corrosion or rust. This is known as atmospheric corrosion.
Atmospheric corrosion typically shows a corrosion rate that is associated with the type of atmosphere a metal is located in, such as marine, rural or industrial. Industrial settings display the presence of a mixture of several contaminants. The data suggests that photochemical smog replicates the industrial atmospheres that are associated with increased corrosion rates.