Under the Environment Protection Act, 1986, the Central Pollution Control Board (CPCB) sets standards for various pollutants. Which of the following is the correct permissible limit for sulphur dioxide (SO2) in ambient air as per NAAQS 2009 (24-hour average) for residential areas?

• A 20 μg/m³
• B 80 μg/m³ ✓
• C 120 μg/m³
• D 500 μg/m³

Explanation

As per NAAQS 2009, the 24-hour average permissible limit for SO2 in residential or rural areas is 80 μg/m³. The annual average is 50 μg/m³. For industrial areas, the 24-hour limit is 120 μg/m³. The 20 μg/m³ is the WHO guideline, not the Indian NAAQS. The 500 μg/m³ is for industrial areas for some other pollutants. The correct NAAQS value for residential areas is 80 μg/m³.

Reference: Park's Textbook of Preventive and Social Medicine, 26th ed.

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