photochemical smog

Definition

In the 1950s a new type of smog, known as photochemical smog, was first described. The compound when sunlight hits various pollutants in the air and forms a mix of inimical chemicals that can be very dangerous. A photochemical smog is the chemical reaction of sunlight, nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the atmosphere, which leaves airborne particles (called particulate matter) and ground-level ozone. (Wikipedia)