Previous Year Question
In the context of WHO Air Quality Guidelines, consider the following statements:
The 24-hour mean of PM2.5 should not exceed 15 μg/m³ and the annual mean of PM2.5 should not exceed 5 μg/m³.
In a year, the highest levels of ozone pollution occur during the periods of inclement weather.
PM10 can penetrate the lung barrier and enter the bloodstream.
Excessive ozone in the air can trigger asthma.
Which of the statements given above are correct?
1, 3 and 4
1 and 4
2, 3 and 4
1 and 2
Correct Answer: B
Detailed Solution
Statement 1 is correct.
The WHO updated its Global Air Quality Guidelines in 2021.
The WHO-recommended annual average level for PM2.5 is 5 μg/m³.
The recommended 24-hour average level for PM2.5 is 15 μg/m³.
These are health-based guideline levels; they do not automatically become the legal or regulatory standards of every country.
PM2.5 has a diameter of 2.5 micrometres or less.
Its major sources include the combustion of fossil fuels and biomass, vehicular emissions, industries and secondary particle formation.
Long-term exposure to PM2.5 can increase the risk of cardiovascular and respiratory diseases.
Statement 2 is incorrect.
High levels of ground-level ozone generally form during hot, dry and sunny weather, not necessarily during inclement weather.
Ground-level ozone is not directly emitted in large quantities; it is formed through photochemical reactions in the atmosphere.
In the presence of sunlight, nitrogen oxides and volatile organic compounds react with each other to form ozone.
Therefore, ozone pollution can be higher during stable sunny days in summer.
Adverse weather conditions such as strong winds, rainfall and clouds can reduce ozone formation and accumulation under many circumstances.
Therefore, the assertion that the highest levels of ozone pollution occur during periods of inclement weather is incorrect.
Statement 3 is incorrect.
PM10 includes particles having a diameter of 10 micrometres or less.
PM10 can enter the respiratory system, and its smaller particles can reach inside the lungs.
However, the ability to cross the lung barrier and enter the bloodstream is mainly associated with finer PM2.5 and ultrafine particles.
Relatively larger PM10 particles may primarily settle in the nose, throat and upper respiratory tract.
Therefore, the broad assertion made regarding PM10 is incorrect.
Statement 4 is correct.
Ground-level ozone is a powerful oxidising pollutant.
It can cause irritation and inflammation in the respiratory tract.
Exposure to ozone can cause coughing, throat irritation, difficulty in breathing and reduced lung function.
It can trigger an asthma attack or aggravate its symptoms in a person already affected by asthma.
Children, elderly persons, outdoor workers and individuals affected by respiratory diseases may be more susceptible.
Ground-level ozone is a pollutant, whereas the stratospheric ozone layer protects Earth from the Sun’s harmful ultraviolet radiation.