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Q.
The brown haze of photochemical smog is largely attributable to:
Punjab PMETPunjab PMET 2006The p-Block Elements - Part2
Solution:
Photochemical smog is initiated by the photochemical dissociation of $NO _{2}$ and the resulting secondary reactions involving unsaturated hydrocarbons, other organic compounds and free radicals, leading to the formation of organic peroxides and ozone,
$NO_2(g) \xrightarrow{\text{UV light}} NO(g) + [O]]$
$O_2(g) + [O] \to O_3(g)$
Hydrocarbons $+ O _{3}, O _{2}, O , NO _{2}$, NO :
Peroxides, peroxyacetyl nitrate, formaldehyde, ozone aldehyde, acrolein etc. (oxidized hydrocarbons)
These oxidized hydrocarbons and ozone in the presence of humidity cause photochemical smog, which dissipates at night.