Question
In the context of WHO Air Quality Guidelines, consider the following statements:
1. The 24-hour mean of PM2.5 should not exceed 15 ug/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?
Explanation
Correct answer: (b) 1 and 4 only
Statement 1 is correct: WHO’s 2021 Global Air Quality Guidelines set the recommended 24-hour mean PM2.5 limit at 15 µg/m³ and the annual mean at 5 µg/m³.
Statement 2 is incorrect: Ground-level ozone is a secondary photochemical pollutant formed when precursor gases react in strong sunlight — so it peaks in hot, sunny weather, not overcast conditions.
Statement 3 is incorrect: Coarse PM10 penetrates the upper respiratory bronchi; it’s the finer PM2.5/PM0.1 that crosses the alveolar-capillary barrier into the bloodstream.
Statement 4 is correct: Ground-level ozone is an oxidising irritant that damages airway tissue, triggering bronchospasms and asthma exacerbations.