Question

The primary pollutant that leads to photochemical smog is :

• A. sulphur dioxide
• B. acrolein
• C. ozone
• D. nitrogen oxides

Answer 1

The Correct Option is D

Photochemical smog is a type of air pollution that results from the reaction of sunlight with pollutants in the atmosphere. The main pollutants involved in the formation of photochemical smog are nitrogen oxides (NO_x) and volatile organic compounds (VOCs). Let's analyze the given options to determine the primary pollutant that leads to photochemical smog:

1. Sulphur dioxide (SO₂): Although sulphur dioxide is a significant air pollutant contributing to acid rain and respiratory problems, it is not a primary contributor to photochemical smog. Therefore, this option is incorrect.
2. Acrolein (C₃H₄O): Acrolein is an organic compound and a VOC, but it is not the primary pollutant responsible for photochemical smog. VOCs react with nitrogen oxides in the presence of sunlight to form smog, but it is the nitrogen oxides that are the main trigger. This option is incorrect.
3. Ozone (O₃): Ozone is a major component of photochemical smog but it is not a primary pollutant. Instead, it is a secondary pollutant formed as a result of chemical reactions between primary pollutants like nitrogen oxides and VOCs in the presence of sunlight. Thus, this option is incorrect.
4. Nitrogen oxides (NO_x): Nitrogen oxides are primary pollutants emitted from vehicles, industrial processes, and combustion of fossil fuels. They are crucial in the formation of photochemical smog as they react with VOCs under sunlight to produce ozone and other smog particles. Therefore, nitrogen oxides are indeed the primary pollutants leading to photochemical smog. This option is correct.

Based on the analysis above, the primary pollutant that leads to the formation of photochemical smog is nitrogen oxides (NO_x).