In the context of WHO Air Quality Guidelines, Consider the following statements. Which of the statements given above are correct?


05:23 AM

UPSC Prelims 2022 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 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

a) 1 and 2 only

Correct Answer: Option b) 1 and 4 only

Learn more about WHO Air Quality Guidelines in the given explanation below.


According to WHO Air Quality Guidelines, the annual average concentrations of PM2.5 should not exceed 5 µg/m3, while 24-hour average exposures should not exceed 15 µg/m3 more than 3 - 4 days per year. So, statement 1 is correct.

WHO Air Quality Guidelines

  • Some pollution, such as ground-level ozone, is made more efficiently in sunny, hot weather. The reactions that create harmful ozone in our atmosphere require sunlight. In the summers and especially during extreme heat waves, ozone often reaches dangerous levels in cities or nearby rural areas. Humidity can help to decrease ozone pollution. Afternoon thunderstorm clouds block sunlight, causing ozone production to slow down for the day, while moisture from the storm destroys the ozone that has formed. So, statement 2 is not correct.
  • Studies have shown that PM with a diameter of 10 μm (PM10) can enter the lungs but not the bloodstreams. PM particles with a diameter of 2.5 μm or less (PM2.5) can further reach the distal lung segments, including the alveoli, pass into the bloodstream, and are capable of penetrating blood-organ barriers affecting multiple organ systems, such as the brain, heart, liver and kidney. So, statement 3 is not correct.
  • Ozone pollution is the result of hydrocarbons and nitrogen oxide emissions from motor vehicles or other sources, mixed in the presence of sunlight. It causes increased wheezing, coughing, and chest tightness, especially among susceptible children who play outdoors in polluted environments. Excessive ozone can trigger asthma because it is very irritating to the lungs and airways. So, statement 4 is correct.

Therefore, option (b) is the correct answer.

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