Question

According to the origin, identify the secondary air pollutant.
A. $SO_2$
B. Ash
C. Ozone
D. Radioactive compound

Answer 1

Hint: The factors and substances that cause air pollution are called air pollutants. Air pollution is both natural and anthropogenic. The air pollutants that come directly from the pollution sources are called primary pollutants, for example, the exhaust from a car burning gas. The pollutant produced by the reaction between two or more primary pollutants to form other pollutants is known as secondary pollutants. The fumes from exhaust mix with the oxygen in the air to form nitrogen dioxide are an example of a secondary pollutant.

Complete Answer:
- The ground-level ozone is colorless and highly irritating gas which forms just above the earth's surface. It is known as a secondary pollutant because it is formed when the two primary molecules interact with each other in the presence of sunlight and stagnant air. The two primary pollutants which react with each other are nitrogen oxide (NO) and a volatile organic compound.
- They both come from natural resources as well as human activities. The major sources of NOX originate from anthropogenic activities i.e. from the burning of coal, gasoline, and oil in motor vehicles. VOCs are originating from human activity like gasoline combustion, upstream oil and gas production, and residential wood combustion, etc.
- Ozone is a secondary pollutant as it is not emitted directly but is produced in a cycle of reactions having two basic classes of compounds i.e. nitrogen oxide and hydrocarbon.

Therefore the correct option is ozone.

Note: Ozone is formed by a reaction between nitrogen oxides and VOC in the presence of sunlight. This is a secondary pollutant because this is formed by the reaction between more than two primary pollutants that react to form the secondary pollutant. It does not come directly from the source.