In the context of WHO Air Quality Guidelines, consider the following statements:

1. The 24-hour mean of PM_2.5should not exceed 15 µg/m³ and annual mean of PM_2.5should not exceed 5 µg/m³.
2. In a year, the highest levels of ozone pollution occur during the periods of inclement weather.
3. PM₁₀can 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?

[UPSC Civil Services Exam – 2022 Prelims]

(a) 1, 3 and 4

(b) 1 and 4 only

(c) 2, 3 and 4

(d) 1 and 2 only

Answer: (b)        

Explanation:

• The WHO Air Quality Guidelines are evidence-based recommendations for limit values of specific air pollutants, designed to protect public health.
• The guidelines were first introduced in 1987 and cover pollutants such as particulate matter, ozone, nitrogen dioxide, sulfur dioxide, and carbon monoxide.
• The guidelines state that annual mean levels of PM2.5 should not exceed 5 μg/m3, while 24-hour mean levels should not exceed 15 μg/m3. Similarly, annual mean levels of PM10 should not exceed 15 μg/m3, while 24-hour mean levels should not exceed 45 μg/m3.
• PM10 particles can pass through the nose and throat to enter the lungs, potentially causing serious health effects. However, PM2.5 particles are even more harmful as they can penetrate deep into the lungs and enter the bloodstream.
• High ozone concentrations can cause severe health effects, especially in areas with already high levels or during periods of hot weather.
• Ozone can trigger asthma attacks due to its irritant effects on the lungs and airways.
• Therefore, statements 1 and 4 are correct, while statements 2 and 3 are incorrect.