Photochemical smog is a mixture of air pollutants which have been chemically altered into further noxious compounds by exposure to sunlight. The main components of photochemical smog are nitrogen oxides, Volatile Organic Compounds (VOCs), tropospheric ozone, and PAN (peroxyacetyl nitrate).

Chlorofluorocarbons are responsible for ozone layer depletion. Chlorofluorocarbon is not a component of the smog as it takes part in the depletion of the ozone layer. This depletion can result in climate changes but it is not part of the smog.