Under the Indian National Ambient Air Quality Standards (2009), what is the permissible annual average concentration for PM2.5 in industrial and residential areas?
- A20 μg/m3
- B40 μg/m3Correct
- C60 μg/m3
- D100 μg/m3
Solution
Concept
National Ambient Air Quality Standards (NAAQS 2009) for PM2.5
Formula
NAAQS Limits: PM2.5 Annual = 40 ug/m3, 24-hr = 60 ug/m3; PM10 Annual = 60 ug/m3, 24-hr = 100 ug/m3
Step-by-step solution
1. NAAQS 2009 specifies standards for 12 criteria air pollutants. 2. For fine particulate matter PM2.5, annual permissible concentration is 40 µg/m³. 3. The 24-hour average standard for PM2.5 is 60 µg/m³. 4. Therefore, the annual average limit is 40 µg/m³. Answer: B
Explanation
Under the Central Pollution Control Board (CPCB) National Ambient Air Quality Standards (NAAQS, November 2009), the permissible annual average concentration for Particulate Matter less than 2.5 microns (PM2.5) in Industrial, Residential, Rural, and other Ecologically sensitive areas is 40 µg/m³ (with a 24-hour average of 60 µg/m³).
Why the other options are wrong
A) 20 µg/m³ is not an Indian standard limit for PM2.5. C) 60 µg/m³ is the 24-hour limit for PM2.5 (and annual limit for PM10). D) 100 µg/m³ is the 24-hour limit for PM10.
Shortcut
PM2.5 limits: 40 µg/m³ (Annual) / 60 µg/m³ (24-hr). PM10 limits: 60 µg/m³ (Annual) / 100 µg/m³ (24-hr).
Common mistake
Confusing PM2.5 annual standard (40 µg/m³) with PM10 annual standard (60 µg/m³) or 24-hour standard (60 µg/m³).
Correct answer: B) 40 μg/m3