In the context of WHO Air Quality Guidelines, consider the following statements:1.The 24-hour mean of PM 2.5 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?

1. A

   1, 3 and 4

   1, 3 and 4. PM10 is coarser; PM2.5 is the fraction that more readily enters blood. Ozone peaks in sunshine, not ‘inclement weather’.

2. B

   1 and 4 only

   1 and 4 only. WHO 2021: PM2.5 15 µg/m³ (24 h) and 5 µg/m³ (annual). Ozone aggravates asthma. 2 and 3 fail.

3. C

   2, 3 and 4

   2, 3 and 4. 2 and 3 are the misses.

4. D

   1 and 2 only

   1 and 2 only. Statement 2 is false.

Summary. Official key is (b) 1 and 4 only. The 2021 WHO AQG numbers for PM2.5 are 15 (24-hour) and 5 (annual) µg/m³. Ozone is a photochemical summer pollutant and an asthma trigger. Inclement weather is not ozone’s peak; PM10 is not the particle that typically crosses into blood the way ultrafines/PM2.5 are discussed.