Solution

Photochemical smog is formed from secondary pollutants. It is formed due to automobile exhausts. Nitrogen dioxide splits into nitric oxide and nascent oxygen. Nascent oxygen forms ozone. Ozone, nitric oxide and hydrocarbons form PAN. Carbon dioxide is not related to formation of Photochemical smog. Carbon dioxide is an important green house gas and increased production of carbon dioxide leads to global warming. Thus, the correct answer is option A.