Consider the following : 1. Carbon monoxide 2. Nitrogen oxide 3. Ozone 4. Sulphur dioxide Excess of which of the above in the environment is/are cause(s) of acid rain ?
- (a) 1, 2 and 3
- (b) 2 and 4 only ✓ UPSC's answer
- (c) 4 only
- (d) 1, 3 and 4
Why the answer is (b)
• Acid rain forms when sulphur dioxide and nitrogen oxides emitted from burning fossil fuels react with water and oxygen in the atmosphere to form sulphuric and nitric acids — items 2 and 4.
• Carbon monoxide is a toxic pollutant but does not form acids in rain.
• Ozone at ground level is a photochemical oxidant harmful to lungs and crops, but it is not a cause of acid rain.
• Acid rain damages forests, lakes, soils and monuments such as the Taj Mahal.
• Hence 2 and 4 only, option (b).
Why the other options are wrong
- (a) 1, 2 and 3
- Carbon monoxide and ozone do not cause acid rain.
- (c) 4 only
- Nitrogen oxides also cause acid rain, not sulphur dioxide alone.
- (d) 1, 3 and 4
- Carbon monoxide and ozone are not acid-rain precursors.
Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2022, held on 5 June 2022. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.