In the context of WHO Air Quality Guidelines, consider the following statements : 1. The 24-hour mean of PM₂·₅ should not exceed 15 µg/m³ and annual mean of PM₂·₅ should not exceed 5 µg/m³. 2. In a year, the highest levels of ozone pollution occur during the periods of inclement weather. 3. PM₁₀ can penetrate the lung barrier and enter the bloodstream. 4. Excessive ozone in the air can trigger asthma. Which of the statements given above are correct ?
- (a) 1, 3 and 4
- (b) 1 and 4 only ✓ UPSC's answer
- (c) 2, 3 and 4
- (d) 1 and 2 only
Why the answer is (b)
• Statement 1 is correct: the WHO's 2021 Air Quality Guidelines set the annual mean for PM₂·₅ at 5 µg/m³ and the 24-hour mean at 15 µg/m³, far stricter than India's standards.
• Statement 4 is correct: ground-level ozone irritates the airways and can trigger asthma attacks and reduce lung function.
• Statement 2 is wrong: ozone pollution peaks in sunny, hot, stagnant weather, when sunlight drives reactions between nitrogen oxides and volatile organic compounds — not in inclement weather.
• Statement 3 is wrong: it is the finer PM₂·₅ that penetrates the lung barrier into the bloodstream; PM₁₀ is largely trapped in the upper airways.
• Hence 1 and 4 only, option (b).
Why the other options are wrong
- (a) 1, 3 and 4
- Statement 3 is wrong: PM₂·₅, not PM₁₀, enters the bloodstream.
- (c) 2, 3 and 4
- Statements 2 and 3 are wrong; statement 1 is correct.
- (d) 1 and 2 only
- Statement 2 is wrong: ozone peaks in sunny, not inclement, weather.
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.