Question

Which of the following is a secondary pollutant?
a. $S{O_2}$
b. $CO$
c. ${O_3}$
d. $C{O_2}$

Answer 1

Hint: As we know that air pollutants can be solid, liquid or gases. Secondary pollutants are formed in the atmosphere and are not emitted directly from any source such as vehicles or power plants, etc. When the primary pollutants which are formed by the combustion process react in the atmosphere to form secondary pollutants. It blocks the Ultra violet rays which are harmful and are coming directly from the sun.

Complete answer:
Pollutants which are emitted from any source in the environment are known as primary pollutants. Secondary pollutants are formed in the atmosphere and are not emitted directly from any source such as vehicles or power plants, etc.
Secondary pollutants are formed when the primary pollutants which are formed by the combustion process react in the atmosphere and it is harmful for humans. Photochemical smog is made up of secondary pollutants i.e. ozone, nitric acid, etc.
Photochemical smog is produced by the interaction of primary pollutants with molecules present in air such as oxygen, hydrocarbons, etc. Secondary pollutants such as: Ozone, Nitrogen oxide, Nitric acid, etc.
Option (a)$S{O_2}$- It is the main source of acid rain. It is released in the atmosphere due to the human activities such as burning of coal, oil, etc. so it is the primary pollutant.
Option (b) $CO$- It is formed due to the incomplete combustion of organic matter and is released directly in the atmosphere so it is also the primary pollutant.
Option (c) ${O_3}$ – Tropospheric ozone or bad ozone is formed by elements such as $CO$, nitrogen oxide reacts in presence of sunlight. Stratospheric ozone protects the planet from UV rays. It is a secondary pollutant.
Option (d) $C{O_2}$- It is a greenhouse gas and is emitted directly into the atmosphere. It is a primary pollutant.

Hence, the correct answer is Option (c) i.e. ${O_3}$ as it is a secondary pollutant.

Note:
Air pollutants can be solid, liquid or gases. Secondary pollutants are formed in the atmosphere and are not emitted directly from any source such as vehicles or power plants, etc. Pollutants which are emitted from any source in the environment are known as primary pollutants. Tropospheric ozone is formed by elements such as $CO$, nitrogen oxide reacts in presence of sunlight. Stratospheric ozone protects the planet from Ultraviolet rays.