Question

The pollutants which come directly in the air from sources are called primary pollutants. Primary pollutants are sometimes converted into secondary pollutants. Which of the following belongs to secondary air pollutants?
(A) CO
(B) Hydrocarbon
(C) Peroxyacetyl nitrate
(D) NO

Answer 1

The compound that contains the word ‘peroxy’, a peroxide linkage is present in the compound as its name suggests. Most of the peroxides are formed by free radical pathways and in atmosphere free radical reactions are possible as light is there in the daytime.

Complete answer:
As said in the question, a secondary pollutant is produced by reaction of a primary pollutant.
Carbon monoxide is released into the air by exhausts of automobiles directly. So, it is a primary pollutant.
Hydrocarbons are also primary pollutants as they are not produced from other pollutants.
Nitrogen oxide is released into the atmosphere by combustion of nitrogen containing fuel and some other natural phenomenons like volcanoes, etc... So, it is also a primary pollutant.
Now, peroxyacetyl nitrate is not a primary pollutant and it is produced from Nitrogen dioxide via free radical intermediate.
So, correct answer is (C) Peroxyacetyl nitrate

Additional Information:
Let’s see how Peroxyacetyl nitrate is produced.

We can see that acetate radicals and nitrate radicals combine and form Peroxyacetyl nitrate. Acetate and nitrate radicals are present in the atmosphere.

Note: Do not think that as NO can be obtained from $N{O_2}$, it could be termed as a secondary pollutant. It is produced directly as well. That’s why it is a primary pollutant only. Note that ozone is also a secondary pollutant.