UPSC Prelims 2022 Q44: Environment & Ecology – Pollution & Waste Management
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
- (c) 2, 3 and 4
- (d) 1 and 2 only
Answer: (b) 1 and 4 only
Explanation
WHO Air Quality Guidelines (2021)
| Statement | Verdict | Fact |
|---|---|---|
| 1. PM2.5: 24-hour mean ≤ 15 μg/m³, annual mean ≤ 5 μg/m³ | Correct | These are the 2021 WHO guideline values, tightened from 25 and 10 |
| 2. Ozone peaks in inclement weather | Incorrect | Ground-level ozone forms by sunlight-driven reactions, so it peaks in hot, sunny weather |
| 3. PM10 can cross the lung barrier into blood | Incorrect | PM2.5 (and ultrafine particles) can enter the bloodstream; PM10 lodges in the airways |
| 4. Excess ozone can trigger asthma | Correct | Ozone inflames airways and is a known asthma trigger |
Size matters:
| Particle | Size | Reaches |
|---|---|---|
| PM10 | ≤ 10 microns | Nose, throat, upper airways |
| PM2.5 | ≤ 2.5 microns | Deep lungs (alveoli) and bloodstream |
Answer: (b) 1 and 4 only.
Why each option is right or wrong
- (a) Incorrect. Statement 3 is wrong: it is PM2.5, not PM10, that crosses into the bloodstream.
- (b) CORRECT. The 2021 PM2.5 limits (15 and 5 μg/m³) and ozone's role in asthma are both accurate.
- (c) Incorrect. Ozone peaks in sunny weather, not inclement weather, and PM10 does not enter the blood.
- (d) Incorrect. Statement 2 is false because ozone needs strong sunlight to form.
Key point
WHO 2021: PM2.5 annual 5 μg/m³ and 24-hour 15 μg/m³; PM2.5 (not PM10) enters the blood; ozone peaks in sunny weather.
Remember
WHO 2021 PM2.5: 5 annual, 15 daily; ozone = sunny-day pollutant.
Common mistakes
- Thinking ozone peaks in bad weather; it is a photochemical pollutant that needs sunlight.
- Swapping PM10 and PM2.5 when asked which particle reaches the bloodstream.
- Recalling the old 2005 limits (25 and 10 μg/m³) instead of the 2021 revision.
Exam tip
Smaller particle, deeper damage. PM10 stops in the airways; PM2.5 reaches the alveoli and blood.
Sources
- WHO Global Air Quality Guidelines (September 2021)
- Central Pollution Control Board — National Ambient Air Quality Standards