Question

The photochemical smog is essentially caused by presence of:

• A. $O_2$ and $O_3$
• B. Oxides of nitrogen and hydrocarbons
• C. Oxides of sulphur and nitrogen
• D. $O_2$ and $N_2$

Answer 1

The correct option is B Oxides of nitrogen and hydrocarbons

Photochemical smog is a smog caused when UV light from the Sun reacts with nitrogen oxides and hydrocarbons in the atmosphere. It is visible as haze and is most prominent during morning and afternoon. The main chemical pollutant they monitor is Ozone. Besides Ozone, photochemical smog contains a number of other pollutants as well such as PAN $\to$ Peroxyacetyl nitrate, nitrous acid, nitric acid.
So, Smog is caused by oxides of sulphur and nitrogen but photochemical smog is caused by the chemical reaction between UV light from Sun and hydrocarbon and oxides of nitrogen.

Hence, the correct answer is option (b).