In sunlight, tropospheric ozone builds up in smog through NO2 -> NO + O, O + O2 -> O3 and O3 + NO -> NO2 + O2. These three steps alone do not allow ozone to accumulate. Ozone accumulates in practice because

peroxy radicals from hydrocarbon oxidation convert NO to NO2 without consuming ozone

NO2 is not photolysed at ground level

hydrocarbons react directly with O2 to give O3

NO is converted into N2 by the sunlight

peroxy radicals from hydrocarbon oxidation convert NO to NO2 without consuming ozone

JEE Advanced levelSingle correct optionDifficulty 3 of 3ev096

In sunlight, tropospheric ozone builds up in smog through $NO X_{2} NO + O$ , $O + O X_{2} O X_{3}$ and $O X_{3} + NO NO X_{2} + O X_{2}$ . These three steps alone do not allow ozone to accumulate. Ozone accumulates in practice because

A $NO X_{2}$ is not photolysed at ground level
Bhydrocarbons react directly with $O X_{2}$ to give $O X_{3}$
CNO is converted into $N X_{2}$ by the sunlight
Dperoxy radicals from hydrocarbon oxidation convert NO to $NO X_{2}$ without consuming ozone

The three steps form a closed cycle in which ozone made is consumed again by NO. Hydrocarbons are oxidised to peroxy radicals that oxidise NO to

NO X_{2}

without using ozone. Each such conversion produces fresh

NO X_{2}

, which photolyses to give more

O

and thus

O X_{3}