A form of smog that characterizes polluted atmospheres where high concentrations of nitrogen oxides and volatile organic compounds--often from gas-driven automobilesmixed with sunlight promote a series of photochemical reactions that lead to the formation of ozone and a range of oxidized and nitrated organic compounds. The smog turns brownish in color and lowers visibility towards the middle of the day as sunlight becomes intense. The smog also causes eye irritation and a range of less distinct short- and long-term health effects. Photochemical smog, though typified by the atmosphere of the Los Angeles Basin, is increasingly found in cities all over the world where volatile fuels are used.