Photochemical smog is a brownish-gray haze caused by the action of solar ultraviolet radiation on atmosphere polluted with hydrocarbons and oxides of nitrogen. It contains anthropogenic air pollutants, mainly ozone, nitric acid, and organic compounds, which are trapped near the ground by temperature inversion. These pollutants and also some others can affect human health and cause damage to plants. Photochemical smog often has an unpleasant odor due to some of its gaseous components. The term smog (not to be confused with photochemical smog) is commonly used to represent a near-ground haze made of a combination of smoke and fog rather than ozone, nitric acid, and organic compounds.
