Photo chemical smog always contains

Photochemical smog is a type of air pollution produced when ultraviolet light from the sun reacts with nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the atmosphere. The most abundant and characteristic component of photochemical smog is ozone (O3), which is a secondary pollutant formed at ground level. Other significant components include peroxyacetyl nitrate (PAN), nitrogen dioxide, and various aldehydes. While methane is a VOC, ground-level ozone is the defining chemical signature always present in such smog. Aluminium ions and phosphorus are not involved in the chemical reactions that lead to the formation of photochemical smog.