Practice question

Photochemical smog follows the pathway nitrogen oxides plus VOCs plus sunlight leading to ozone and PAN. Nitrogen dioxide absorbs light and yields the atomic oxygen needed for ozone formation; VOC oxidation generates peroxy radicals that convert nitric oxide back to nitrogen dioxide without removing ozone. Acyl peroxy radicals combine with nitrogen dioxide to form peroxyacyl nitrates. The other proposed sequences omit essential photochemistry or combine unrelated substances. Atmospheric inversions can trap contaminants near the surface, while wind, turbulence, precipitation, and chemical transformation determine their eventual distribution and removal. At organismal level, respiratory surfaces are especially exposed because large volumes of air contact thin, moist epithelia designed for rapid gas exchange. Sound classification links the source, atmospheric fate, exposure route, and mechanism of toxicity rather than relying only on the pollutant's name. Effective management combines cleaner fuels, emission standards, monitoring, urban planning, and protection of populations with high exposure or physiological vulnerability.