Which of the following air pollutants primarily contributes to the formation of photochemical smog?

Photochemical smog is primarily formed through the interaction of sunlight with various pollutants, particularly nitrogen oxides (NOx) and volatile organic compounds (VOCs). Among these pollutants, volatile organic compounds are considered the primary contributors to the formation of photochemical smog. When VOCs are released into the atmosphere, they react with nitrogen oxides in the presence of sunlight, leading to the formation of ozone at ground level and other secondary pollutants, which together comprise photochemical smog.

In summary, while both nitrogen oxides and volatile organic compounds play roles in the formation of photochemical smog, VOCs are typically the primary contributors.