UPSC Prelims 2022 · GS Paper I
Question 44: Environment and Ecology
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 ?
AnswerUPSC’s answer is (b).
WHO's 2021 guidelines set PM2.5 at 15 µg/m³ for the 24-hour mean and 5 µg/m³ for the annual mean, so statement 1 is true. Excess ozone irritates the airways and can trigger asthma, so statement 4 is true. Ozone forms in strong sunlight and heat, so it peaks in summer, not in inclement weather. It is the finer PM2.5, not PM10, that can cross the lung barrier into the bloodstream.
- 1. WHO 2021 limits: 15 µg/m³ for 24 hours and 5 µg/m³ annually for PM2.5.
- 2. Ozone peaks in hot, sunny weather, not in inclement weather.
- 3. The finer PM2.5 enters the bloodstream; PM10 is mostly stopped higher up.
- 4. Excess ozone can trigger asthma.
How you could have got this
- If you were sure statement 2 is not correct, (c) and (d) go: each of them includes 2.
What you needed to know: Ozone peaks in hot, sunny weather, not in inclement weather.
- Then, if you were sure statement 3 is not correct, (a) goes: it includes 3.
What you needed to know: The finer PM2.5 enters the bloodstream; PM10 is mostly stopped higher up.
Only (b) is left. You didn’t need statements 1 or 4.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Wrong. Statement 3 is false: PM2.5, not PM10, enters the bloodstream.
- (b) Correct. Statements 1 and 4 hold.
- (c) Wrong. Statements 2 and 3 are false.
- (d) Wrong. Statement 2 is false and statement 4 is missing.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2022, General Studies Paper I, Series A. The paper on upsc.gov.in.