The Air Quality Index (AQI) in India uses which pollutant as the primary indicator for categorizing air as 'Hazardous' (AQI 401–500)?
- A PM2.5 alone
- B PM10 alone, as it is the regulated standard pollutant
- C Any one of the eight measured pollutants that gives the highest sub-index value ✓
- D Ozone, as it is the most toxic pollutant
Correct answer: C. Any one of the eight measured pollutants that gives the highest sub-index value
Explanation
The Indian AQI is calculated for eight pollutants: PM10, PM2.5, NO₂, SO₂, CO, O₃, NH₃, and Pb. Sub-indices are calculated for each pollutant using NAAQ Standards, and the overall AQI for a monitoring station equals the maximum sub-index value across all available pollutant sub-indices (worst-first approach). This means if any one pollutant has a sub-index in the 'Hazardous' range (401–500), the overall AQI is 401–500 regardless of other pollutants. This single-pollutant worst-case approach ensures the most hazardous condition is communicated to the public.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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