A city monitors ambient air quality under India's National Ambient Air Quality Standards (NAAQS, 2009). The 24-hour average standard for PM2.5 is:

• A 15 µg/m³
• B 60 µg/m³ ✓
• C 40 µg/m³
• D 100 µg/m³

Explanation

India's NAAQS 2009 (prescribed by CPCB) set the 24-hour average standard for PM2.5 at 60 µg/m³ and the annual average at 40 µg/m³. In contrast, WHO's updated 2021 Air Quality Guidelines recommend 24-hour PM2.5 of 15 µg/m³ and annual average of 5 µg/m³ — far more stringent than India's current standards. PM2.5 penetrates deep into the alveoli and is associated with cardiovascular disease, lung cancer, and premature mortality.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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