Which component of smog causes eye irritation?
Peroxyacetyl nitrate, commonly represented within the broader term PAN, is a secondary component of photochemical smog and a powerful lachrymator. It forms when VOC oxidation products react with nitrogen dioxide and can irritate conjunctival and respiratory tissues. Carbon monoxide mainly produces systemic hypoxia without being a strong eye irritant, while lead and mercury are toxic metals rather than characteristic lachrymatory smog components. Exposure depends on concentration, duration, ventilation, weather, and individual susceptibility, so a pollutant's presence alone does not fully predict biological harm. 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.
Ref: Campbell Biology, Urry et al., 12th Ed., Unit 8 Ecology