Peroxyacyl nitrates or PANs are a component of photochemical smog, produced in the atmosphere when oxidized volatile organic compounds combine with nitrogen oxide. They are a secondary pollutant since they form in the atmosphere after the emission of primary pollutants. Sources of the pollutants required to create PANs include motor vehicles, tobacco smoke, and the burning of fossil fuels.
PANs have many adverse effects in the human body such as reduced respiratory function and eye irritation, and may also be linked to emphysema, impaired breathing and other lung problems. Human exposure to PANs typically occurs in urban centers where automobile and industrial emissions are high.
PANs have a lifetime of about 3 months in atmosphere at cold temperatures of around -20°C, however in warmer areas it is typically only a few hours. The implications of PANs that remain in the atmosphere for extended periods of time are of concern, since they can be transported large distances thereby spreading their environmental impact to other regions. Under these conditions PANs can contribute to air pollution in places far away from their source.