1. The 24-hour mean of PM2.5 should not exceed 15 ug/m3 and annual mean of PM2.5 should not exceed 5 ug/m3.
2. In a year, the highest levels of ozone pollution occur during the period 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
The updated (2021) WHO Global Air Quality Guidelines (AQGs) provide recommendations on air quality guideline levels as well as interim targets for six key air pollutants. The guidelines focus on so-called classical pollutants, particulate matter (PM. and PM), ozone (O₃), nitrogen dioxide (NO₂), sulfur dioxide (SO₂) and carbon monoxide (CO).
Statement 1 is correct: The 24-hour ceiling mean of PM 2.5 used to be 25 micrograms but has now dropped to 15.
Statement 2 is incorrect: Ozone at ground level is formed by the reaction with sunlight (photochemical reaction) of pollutants such as nitrogen oxides (NOx) from vehicle and industry emissions and volatile organic compounds (VOCs) emitted by vehicles, solvents and industry. As a result, the highest levels of ozone pollution occur during periods of sunny weather and not during inclement weather.
Statement 3 is incorrect: Particles with a diameter of 10 m (PM10) can reach the lungs but cannot enter the bloodstream. However, particles with a diameter of 2.5 m or less can penetrate deeper into the lungs, reaching the alveoli, enter the bloodstream, and potentially cross blood-organ barriers, impacting various organs such as the brain, heart, liver, and kidneys. PM (10 microns) can reach deep into the lungs, but the more harmful PM. (2.5 microns) can penetrate the lung barrier and enter the bloodstream, posing severe health risks.
Statement 4 is correct: Excessive ozone in the air can have a marked effect on human health. It causes breathing problems, triggers asthma, reduces lung function and causes lung diseases. Ozone triggers asthma because it is very irritating to the lungs and airways.