Under the National Ambient Air Quality Standards (NAAQS) 2009, what is the 8-hour standard for carbon monoxide in industrial, residential and rural areas of India?

• A 1 mg/m³
• B 2 mg/m³ ✓
• C 4 mg/m³
• D 10 mg/m³

Explanation

The NAAQS 2009 sets carbon monoxide at 2 mg/m³ for the 8-hour average and 4 mg/m³ for the 1-hour average, applicable uniformly across industrial, residential, rural and ecologically sensitive areas. Option C is the 1-hour value, the commonest distractor. Carbon monoxide binds haemoglobin with over 200 times the affinity of oxygen, forming carboxyhaemoglobin and causing tissue hypoxia.

Reference: Central Pollution Control Board, National Ambient Air Quality Standards 2009, NAAQS notification ed.

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