In the context of WHO Air Quality Guidelines, consider the following statements: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?
✓ Correct answer: b) 1 and 4 only
ExplanationThe 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 (PM₂.₅ and PM₁₀), 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 to15. 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 emis- sions and volatile organic compounds (VOCs) emitted by vehi- cles, 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 μm (PM10) can reach the lungs but cannot enter the bloodstream.However, particles with a diameter of 2.5 μm or less can pene- trate deeper into the lungs, reaching the alveoli, ente
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