Question

Which of the following is a secondary pollutant ?

• A. $C{O}_2$
• B. $S{O}_2$
• C. $CO$
• D. $O_3$

Answer 1

The correct option is D $O_3$

Secondary pollutants are pollutants that are not emitted directly from a source. For example: ozone is formed through chemical reactions of other molecules already in the air. So it is considered as a secondary pollutant. These are formed by chemical reaction amongst primary pollutants. For example, photochemical smog, London smog (Classical smog), PAN (Peroxy acetyl nitrate), $O_3$ (Ozone).

So, the correct answer is "option D"