Question

The molecule that has minimum/no role in the formation of photochemical smog is:
A. $C{{H}_{2}}=O$
B. ${{N}_{2}}$
C. ${{O}_{3}}$
D. NO

Answer 1

Photochemical smog is a type of pollution in which the solar radiation reacts with the airborne pollutants which is a mixture of nitrogen oxides $(N{{O}_{x}})$ and hydrocarbons. Chiefly for the build of smog $N{{O}_{2}},{{O}_{3}}$ and hydrocarbons are responsible. $N{{O}_{2}}$ and ${{O}_{3}}$ reacts with hydrocarbons which tends to produce formaldehyde, PAN and acrolein.

Complete answer:
Photochemical smog is a type of a chemical reaction between nitrogen oxides, sunlight and hydrocarbons are organic compounds present in the atmosphere. Photochemical smog always takes place in the presence of sunlight and is visible as a brown haze. This type of smog depends both on the primary pollutants as well as on secondary pollutants. Here the primary pollutants are nitrogen oxides, mainly nitrogen dioxide and nitric oxide and the hydrocarbons of volatile nature. And the secondary pollutants are tropospheric Ozone, aldehydes and peroxyacetyl nitrates(PAN). For the formation of photochemical smog the three main ingredients that are essential are nitrogen oxides, hydrocarbons and sunlight.

The formation of photochemical smog takes place in three stages:

1. In the presence of sunlight nitrogen oxides dissociated in ozone and atoms of oxygen.
2. Then the oxygen atoms react with water molecules and form hydroxyl radicals and these hydroxyl radicals oxidized hydrocarbons and form hydrocarbon radicals.
3. After that oxidation of hydrocarbons will take place and forma class of chemicals that is aldehyde. Lastly aldehyde oxidized into formaldehyde peroxides and aldehyde peroxy acids.

In place of ozone(${{O}_{3}}$), NO and $N{{O}_{2}}$can also react with hydrocarbons to form peroxyacetyl nitrate (PAN). Here the PAN, aldehyde peroxy acids and formaldehyde are present as pollutants.
Therefore NO, ${{O}_{3}}$ and $C{{H}_{2}}=O$ have roles in the formation of smog.

Thus, the correct option will be (B).

Note: The accumulation of volatile organic compounds and ozone with solar energy forms the photochemical smog which appears in brown color which is mainly seen in hot sunny days. The pollution formed here is very harmful for human health and mainly. The main chemical pollutant that is seen is ozone and other photochemical smog pollutants are PAN, nitrous acid and nitric acid.