Question

The pollutants which come directly in the air from sources are called primary pollutants. Which of the following belongs to secondary air pollutants ?
a.) CO
b.) Hydrocarbon
c.) Peroxyacetylnitrate (PAN)
d.) NO

Answer 1

Hint: The secondary pollutant here is the one which does not have a direct source. It is present in photochemical smog. This molecule is an oxidant that is more stable than ozone.

Complete step by step answer:
The secondary air pollutants are not emitted directly from a source but are formed in the atmosphere due to reaction with molecules in the atmosphere.
When we see the options.
We know that CO is formed from the partial oxidation of carbon-containing substances. So, option a.) can not be answered.
Hydrocarbons also have a definite source. So, we can not consider even them
The option c.) which is peroxyacetyl nitrate (PAN) is present in photochemical smog. This is a secondary pollutant and is the correct answer.
The option d.) NO is a gas that is prepared when ammonia reacts with oxygen. Even this has a source. So, option d.) is also incorrect.

Thus, the correct answer is option c.) Peroxyacetyl nitrate (PAN).

Note:
The phenomenon of photochemical smog is because of interactions of primary pollutants with other molecules in the air like Oxygen, water and hydrocarbon etc. It comes under secondary pollution.
The peroxyacetyl nitrate present in photochemical smog is thermally unstable and decomposes easily.