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.