The correct option is D Chlorofluorocarbons
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).
Hence, the correct option is (d)