National Air Quality Index

The National Air Quality Index (AQI) is a public-communication tool launched by the Ministry of Environment, Forest and Climate Change (MoEFCC) on 6 April 2015 in New Delhi under the slogan "One Number — One Colour — One Description". It was developed by the Central Pollution Control Board (CPCB) in consultation with IIT Kanpur and an expert group, operating under the statutory mandate of the Air (Prevention and Control of Pollution) Act, 1981 and Section 16 of the Environment (Protection) Act, 1986. The index translates complex, multi-pollutant monitoring data into a single intuitive value to inform citizens — particularly vulnerable groups — about daily air quality and associated health risks.

The AQI is computed for eight pollutants for which the National Ambient Air Quality Standards (NAAQS, notified 2009) prescribe limits: PM2.5, PM10, nitrogen dioxide (NO₂), sulphur dioxide (SO₂), carbon monoxide (CO), ozone (O₃), ammonia (NH₃) and lead (Pb). For each pollutant a sub-index is calculated from its averaging-period concentration, and the worst (maximum) sub-index determines the overall AQI for that station, provided data for at least three pollutants — one of which must be PM2.5 or PM10 — are available. The 0–500 scale is divided into six categories: Good (0–50), Satisfactory (51–100), Moderate (101–200), Poor (201–300), Very Poor (301–400) and Severe (401–500), each with a distinct colour and health advisory. PM2.5 and PM10 use a 24-hour average; CO and O₃ use an 8-hour average.

The AQI feeds operational responses such as the Graded Response Action Plan (GRAP) in the Delhi-NCR, where "Severe+" or "Emergency" readings trigger curbs on construction, diesel generators and entry of trucks. Real-time AQI is disseminated through the SAMEER app and the CPCB website. The monitoring backbone has expanded under the National Clean Air Programme (NCAP, launched January 2019), which set a target — later revised to a 40% reduction in PM concentrations by 2025–26 (against a 2017 baseline) for non-attainment cities. By 2026 the network of Continuous Ambient Air Quality Monitoring Stations (CAAQMS) covers most major cities, though gaps in rural and small-town coverage persist, and Indian NAAQS for PM2.5 remain less stringent than the 2021 WHO Air Quality Guidelines.

For the UPSC examination, the AQI recurs in GS Paper III (environment, conservation, pollution) and frequently in Prelims, where questions test the exact list of eight pollutants, the category boundaries, and the dominant-pollutant (maximum sub-index) rule — a common trap is the false claim that the AQI averages pollutant values. It connects to NCAP, GRAP, the NAAQS, and stubble-burning and winter-smog debates over Delhi. Mains answers should locate the AQI within the larger architecture of statutory air-pollution control and critique its limitations: sparse rural monitoring, NAAQS weaker than WHO benchmarks, and the communication-versus-enforcement gap.