Consider the photochemical smog formation process. Which of the following species is responsible for the initiation of the chain reaction leading to the formation of peroxyacetyl nitrate (PAN)?

Solution

1. Photochemical smog involves the oxidation of hydrocarbons in the presence of nitrogen oxides.
2. The reaction is initiated by the formation of the hydroxyl radical ${\text{OH}}^{\bullet }$ from the photolysis of ozone or nitrous acid.
3. The ${\text{OH}}^{\bullet }$ radical abstracts a hydrogen atom from hydrocarbons to form alkyl radicals.
4. These radicals react with oxygen and ${\text{NO}}_2$ to produce peroxyacetyl nitrate (PAN).
5. Hence the answer is (B).