Indian National Ambient Air Quality standards stipulate the maximum…
2022
Indian National Ambient Air Quality standards stipulate the maximum permissible limit of annual mean concentration of PM2.5 to be
Answer: C. 40 µg/m3 — ConceptAn ambient-air standard pairs each pollutant with a specified averaging period; annual and short-term limits are distinct and must not be interchanged.…
- A.
60 µg/m3
- B.
45 µg/m3
- C.
40 µg/m3
- D.
25 µg/m3
Attempted by 2 students.
Show answer & explanation
Correct answer: C
Concept
An ambient-air standard pairs each pollutant with a specified averaging period; annual and short-term limits are distinct and must not be interchanged.
For particulate matter, concentration is expressed in micrograms per cubic metre (µg/m3), and the value must be read from the row for the pollutant and averaging period named in the question.
Application
The 2009 National Ambient Air Quality Standards table lists PM2.5 at 40 µg/m3 for the annual arithmetic mean in both area categories.
Cross-check and contrast
60 µg/m3 belongs to PM2.5’s 24-hour limit (and also PM10’s annual limit), not its annual PM2.5 limit.
45 µg/m3 is not the listed annual or 24-hour PM2.5 value.
40 µg/m3 is the listed annual PM2.5 value.
25 µg/m3 is the WHO 2005 24-hour guideline value for PM2.5; it is not the Indian NAAQS annual limit.
Result
Therefore, the maximum permissible annual mean concentration of PM2.5 is 40 µg/m3.