Mixture of formaldehyde, acrolein, nitric oxide, ozone, and proxy-acyl nitrates (PAN)
Photochemical smog formation -
Emission of nitrogen oxides and hydrocarbons from automobiles exhausts and solar energy by chain of reactions. NO3 and O3 react with unburnt hydrocarbons to produce formaldehyde, aerolein and proxy-acyl nitrates (PAN)
Photochemical smog is a grey or yellowish brown opaque smog having an oxidising environment with a little smoke. Photochemical smog contains secondary pollutants or photochemical oxidants like Nitrogen Oxide, peroxyacetyl nitrates, aldehydes & phenols due to photochemical reactions between nitrogen oxides & unsatured hydrocarbons.