Q51: Which of the following is a secondary air pollutant? - Aquatic Environment, Limnology, Oceanography & Pollution - ICAR AIEEA PG Fisheries Science 14 July 2023 Shift-1 Paper | Agrigyan

Primary pollutants are emitted directly from sources (e.g. $CO$, $CO_2$, $SO_2$, and $NO_x$ from combustion). Secondary pollutants are not emitted directly but form in the atmosphere through chemical or photochemical reactions between primary pollutants and atmospheric precursors. Ground-level (tropospheric) ozone ($O_3$) is a classic secondary pollutant formed when nitrogen oxides ($NO_x$) and volatile organic compounds (VOCs) react in the presence of sunlight.

Option analysis:

• Ozone: Correct, prototypical secondary photochemical pollutant ($O_3$).
• Carbon dioxide: Primary pollutant emitted directly by combustion/respiration.
• Carbon monoxide: Primary pollutant formed by incomplete combustion.
• Sulphur dioxide: Primary pollutant emitted from fossil fuel burning.