Air Quality Index — Revision Notes
⚡ 30-Second Revision
- AQI scale: 0-500, six categories with color codes
- Eight pollutants: PM10, PM2.5, NO2, SO2, CO, O3, NH3, Pb
- Determined by worst-performing pollutant, not average
- GRAP triggers at AQI 200 (Poor category)
- SAFAR: 15-minute updates, 72-hour forecasting
- NCAP target: 20-30% PM reduction by 2024 in 344 cities
- Indian 'Good' PM2.5: 0-30 μg/m³ vs US EPA: 0-12 μg/m³
- Categories: Good(0-50,Green), Satisfactory(51-100,Light Green), Moderate(101-200,Yellow), Poor(201-300,Orange), Very Poor(301-400,Red), Severe(401-500,Maroon)
2-Minute Revision
Air Quality Index (AQI) converts complex air pollution data into a simple 0-500 scale with six color-coded categories. Developed by CPCB under Environment Protection Act 1986, it measures eight pollutants: PM10, PM2.
5, NO2, SO2, CO, O3, NH3, and Pb. The overall AQI is determined by the highest sub-index among all pollutants, ensuring the most dangerous pollutant drives health advisories. Categories range from Good (0-50, Green) to Severe (401-500, Maroon), each with specific health recommendations.
SAFAR system provides advanced monitoring with 15-minute updates and 72-hour forecasting for major cities. The Graded Response Action Plan (GRAP) automatically triggers emergency measures when AQI crosses 200, implementing progressively stringent controls.
National Clean Air Programme (NCAP) 2019 targets 20-30% reduction in PM concentrations by 2024 across 344 non-attainment cities. Key differences from international standards: Indian 'Good' category allows PM2.
5 up to 30 μg/m³ compared to US EPA's 12 μg/m³. Current challenges include inadequate monitoring coverage, data quality issues, and gaps between information availability and effective policy action. Recent developments focus on technology integration, real-time public access, and automated policy responses.
5-Minute Revision
The Air Quality Index represents India's primary environmental communication tool, transforming complex atmospheric data into actionable public information. Established under the Environment Protection Act 1986 and operationalized by CPCB in 2015, AQI measures eight critical pollutants: particulate matter (PM10, PM2.
5), gaseous pollutants (NO2, SO2, CO, O3), and specific toxins (NH3, Pb). The calculation methodology uses sub-indices for each pollutant, with the overall AQI determined by the worst-performing parameter - ensuring that even if seven pollutants show excellent levels, one dangerous pollutant will accurately reflect health risks.
The six-category system provides clear guidance: Good (0-50, Green) allows all activities; Satisfactory (51-100, Light Green) is acceptable for most people; Moderately Polluted (101-200, Yellow) may affect sensitive individuals; Poor (201-300, Orange) requires reduced outdoor activities; Very Poor (301-400, Red) demands significant precautions; and Severe (401-500, Maroon) necessitates avoiding all outdoor activities.
SAFAR (System of Air Quality and Weather Forecasting and Research) represents technological advancement, providing 15-minute real-time updates and 72-hour forecasting through integration with meteorological data.
This system operates in major metropolitan areas, offering location-specific advisories and emergency preparedness capabilities. The Graded Response Action Plan (GRAP) demonstrates AQI's evolution from information tool to policy trigger, automatically implementing emergency measures when AQI crosses 200.
Stage-wise responses include parking fee increases, construction bans, vehicle restrictions, and industrial controls, with the most stringent measures activated above 450. International comparisons reveal significant differences in health protection approaches.
Indian standards are more lenient - the 'Good' category allows PM2.5 concentrations up to 30 μg/m³ compared to US EPA's 12 μg/m³ and WHO's recommended 5 μg/m³. These differences reflect varying balances between health protection and practical implementation constraints.
The National Clean Air Programme (NCAP) 2019 represents comprehensive policy response, targeting 20-30% reduction in PM concentrations across 344 non-attainment cities by 2024. Implementation challenges include inadequate spatial coverage, data quality issues, institutional fragmentation between monitoring and action agencies, and the persistent gap between information availability and effective pollution control.
Recent developments emphasize technology integration through IoT sensors, satellite monitoring, and AI-enhanced forecasting, alongside improved public access through mobile applications and automated alert systems.
Prelims Revision Notes
- AQI Components: Eight pollutants measured - PM10, PM2.5, NO2, SO2, CO, O3, NH3, Pb (remember: India includes NH3 and Pb unlike many international systems)
- Calculation Method: Determined by WORST pollutant sub-index, not average of all pollutants
- Categories and Ranges: Good(0-50), Satisfactory(51-100), Moderately Polluted(101-200), Poor(201-300), Very Poor(301-400), Severe(401-500)
- Color Coding: Green→Light Green→Yellow→Orange→Red→Maroon (sequential progression)
- GRAP Triggers: Stage I(200+), Stage II(300+), Stage III(400+), Stage IV(450+)
- SAFAR Features: 15-minute updates, 72-hour forecasting, meteorological integration, limited to major cities
- NCAP Details: Launched 2019, 344 cities, 20-30% PM reduction target by 2024, baseline year 2017
- International Comparison: Indian PM2.5 'Good' = 0-30 μg/m³, US EPA = 0-12 μg/m³, WHO guideline = 5 μg/m³ annual mean
- Legal Framework: Environment Protection Act 1986, CPCB guidelines 2014, National Green Tribunal orders
- Key Institutions: CPCB (policy), SAFAR-IITM (advanced monitoring), State PCBs (implementation), CAQM (Delhi-NCR coordination)
Mains Revision Notes
- Policy Integration Framework: AQI serves dual role as public information system and policy trigger mechanism, demonstrated through GRAP implementation and NCAP progress tracking
- Institutional Architecture: Multi-level governance involving CPCB (standard setting), SAFAR-IITM (advanced monitoring), State PCBs (implementation), creating coordination challenges
- Technology Evolution: Progression from manual sampling to real-time automated monitoring to predictive forecasting, with emerging integration of IoT, satellite data, and AI
- Health-Environment Nexus: AQI categories directly linked to health advisories, but effectiveness depends on public awareness, behavioral change, and availability of protective alternatives
- Federal Dynamics: Air pollution as state subject with central monitoring standards creates implementation variations and coordination challenges between different government levels
- International Positioning: India's more lenient standards reflect development priorities vs health protection balance, impacting international environmental commitments and trade implications
- Implementation Gaps: Strong monitoring capabilities but weak translation into effective pollution control, highlighting governance challenges in environmental management
- Current Affairs Integration: Regular connection with Delhi pollution crises, judicial interventions, policy announcements, and international climate commitments
- Future Directions: Emphasis on predictive rather than reactive responses, integration with smart city initiatives, and alignment with sustainable development goals
- Evaluation Metrics: Success measured through pollution reduction achievements, public health outcomes, policy response effectiveness, and international standard alignment
Vyyuha Quick Recall
Vyyuha Quick Recall - 'AQI LADDER' Framework: A(ir) Q(uality) I(ndex) L(evels) A(scending) D(anger) D(etermines) E(mergency) R(esponse). Remember the six rungs: Good-Green-Go (0-50), Satisfactory-Light Green-Limited concern (51-100), Moderate-Yellow-Yield caution (101-200), Poor-Orange-Outdoor restrictions (201-300), Very Poor-Red-Real danger (301-400), Severe-Maroon-Stay inside (401-500).
For pollutants, use 'PM-PM-NO-SO-CO-O-NH-Pb' (PM10, PM2.5, NO2, SO2, CO, O3, NH3, Pb). GRAP stages: 'Two-Three-Four-Four-Fifty' (200-300-400-450 trigger points). SAFAR memory: 'Fifteen minutes, Seventy-two hours' (update frequency and forecast range).
NCAP recall: 'Three-Four-Four cities, Twenty-Thirty percent, Twenty-Twenty-Four year' (344 cities, 20-30% reduction, 2024 target).