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?
Answer & explanation
Answer: (b) 1 and 4 only
Statements 1 and 4 are correct. WHO's 2021 guidelines set PM2.5 at 5 µg/m3 a year and 15 µg/m3 over 24 hours, and ozone can trigger asthma. Ozone peaks in hot, sunny weather, not bad weather, and it is PM2.5, not PM10, that WHO says can enter the bloodstream.
- ✓ 1. The WHO Air Quality Guidelines (2021) recommend an annual average of 5 µg/m3 and a 24-hour average of 15 µg/m3 for PM2.5.
- ✗ 2. Ground-level ozone forms when pollutants react in sunlight, so it is most likely to reach unhealthy levels on hot sunny days, not in inclement weather.
- ✗ 3. Both PM2.5 and PM10 can go deep into the lungs, but WHO says only the finer PM2.5 can even enter the bloodstream.
- ✓ 4. Ozone irritates and inflames the airways, aggravates asthma and increases the frequency of asthma attacks.
Remember · WHO 2021: PM2.5 annual 5, 24-hour 15 µg/m3 (PM10: 15 and 45). Ozone peaks on hot sunny days and worsens asthma. Only PM2.5 reaches the blood.
Sources
- WHO, Billions of people still breathe unhealthy air: new WHO data, 4 April 2022 (Internet Archive copy) ↗ “The latest WHO Air Quality Guidelines (2021) recommend the following concentration limits for these pollutants: For PM 2.5 : Annual average 5 µg/m 3 ; 24-hour average 15 µg/m 3”
- WHO, WHO global air quality guidelines: questions and answers (Internet Archive copy) ↗ “PM₂.₅ and PM₁₀ are capable of penetrating deep into the lungs and PM₂.₅ can even enter the bloodstream, primarily resulting in cardiovascular and respiratory impacts.”
- US EPA, Ground-level Ozone Basics (Internet Archive copy) ↗ “Ozone is most likely to reach unhealthy levels on hot sunny days in urban environments, but can still reach high levels during colder months.”
- US EPA, Health Effects of Ozone Pollution (Internet Archive copy) ↗ “Aggravate lung diseases such as asthma, emphysema, and chronic bronchitis. Increase the frequency of asthma attacks.”
Question and answer: UPSC's official GS Paper I (2022, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·