# AQI and GRAP: How air purity is measured, explained 2026-11-08T13:15:19+00:00 | Governance | Indian Opinion Desk Corroboration: 1 independent outlet The Air Quality Index (AQI) is a scale that measures air purity based on eight major pollutants: PM10, PM2.5, nitrogen dioxide, sulphur dioxide, carbon monoxide, ground-level ozone, ammonia, and lead. The index categorises air into six levels: Good, Satisfactory, Moderately Polluted, Poor, Very Poor, and Severe. When pollutants exceed safe standards set by the World Health Organization, the air becomes toxic. In Delhi-NCR, PM2.5 and PM10 particles are the main culprits, entering the bloodstream directly. Contributing factors include low wind speed, Diwali firecrackers, stubble burning in parts of Punjab and Haryana, vehicle emissions, deforestation, and climate change. The Graded Response Action Plan (GRAP), prepared by the Environment Pollution Control Authority, imposes restrictions such as banning truck entry, halting construction, using anti-smog guns, and increasing metro trips to curb pollution. The article notes that on severe pollution days, breathing in Delhi is compared to smoking 21 cigarettes a day. ## Indian Opinion Analysis The explainer frames Delhi's winter air crisis as a recurring public health emergency driven by a mix of local and regional factors. By listing eight pollutants and six AQI categories, it makes the measurement system accessible but offers no new data or official action. The comparison to smoking 21 cigarettes a day is a vivid but unverified claim that dramatises the risk without naming a study. The piece ends by urging both individual and administrative efforts, but leaves unresolved how enforcement of GRAP measures will be sustained or why past restrictions have failed to break the seasonal pattern. ## Coverage - aajtak.in Explanatory article with no government or opposition slant This brief was synthesised by AI from the source linked above. Tags: AQI, Delhi, Environment Pollution Control Authority, GRAP, PM2.5 Canonical: https://indianopinion.org/aqi-and-grap-how-air-purity-is-measured-explained/ License: Summary and commentary (c) Indian Opinion, reusable with attribution. Facts belong to the linked sources. Cite: https://indianopinion.org/aqi-and-grap-how-air-purity-is-measured-explained/#story-in-brief How this brief was made: an AI model read the report linked above and wrote this summary and analysis, which were published automatically. Published briefs are sampled every hour by an automated quality check; the editor verifies its findings and approves corrections, and corrected briefs carry a dated correction line. We do no original reporting. Methodology: https://indianopinion.org/ai-use-policy/