UPSC CSE Prelims
Question 81
In the context of WHO Air Quality Guidelines, consider the following statements :
- 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.
- In a year, the highest levels of ozone pollution occur during the periods of inclement weather.
- PM10 can penetrate the lung barrier and enter the bloodstream.
- Excessive ozone in the air can trigger asthma.
Which of the statements given above are correct ?
View correct answer and explanation
Correct answer: B
Correct Option: B (1 and 4 only)
Explanation: WHO’s 2021 air-quality guideline is 5 µg/m³ annual and 15 µg/m³ 24-hour PM2.5; ozone can aggravate asthma. The other claims are incorrect as phrased.
Statement / Pair / Item-wise Analysis:
1. True / qualifies - The 2021 WHO PM2.5 guideline values are 5 µg/m³ annually and 15 µg/m³ over 24 hours.
2. False / does not qualify - Peak ground-level ozone commonly occurs in hot, sunny, stagnant conditions, not generally in inclement weather.
3. False / does not qualify - PM10 can penetrate airways, but the finer PM2.5 fraction is particularly associated with alveolar penetration and entry into bloodstream; the blanket PM10 claim is not accepted.
4. True / qualifies - Excess ground-level ozone irritates airways and can trigger/worsen asthma.
Option-wise Analysis:
A. Incorrect-includes 3 even though PM10 can penetrate airways, but the finer PM2.5 fraction is particularly associated with alveolar penetration and entry into bloodstream; the blanket PM10 claim is not accepted.
B. Correct-selects exactly the correct statements/items identified above.
C. Incorrect-includes 2 even though Peak ground-level ozone commonly occurs in hot, sunny, stagnant conditions, not generally in inclement weather.; includes 3 even though PM10 can penetrate airways, but the finer PM2.5 fraction is particularly associated with alveolar penetration and entry into bloodstream; the blanket PM10 claim is not accepted.; omits 1 even though The 2021 WHO PM2.5 guideline values are 5 µg/m³ annually and 15 µg/m³ over 24 hours.
D. Incorrect-includes 2 even though Peak ground-level ozone commonly occurs in hot, sunny, stagnant conditions, not generally in inclement weather.; omits 4 even though Excess ground-level ozone irritates airways and can trigger/worsen asthma.
Review note: Ultrafine fractions within a broad PM10 size category can reach deeper tissues; question distinguishes PM10 from PM2.5 in conventional WHO wording.