What Is AQI? India's Air Quality Index Explained Simply
Learn what the Air Quality Index (AQI) means, how it's calculated, and how India's AQI system compares to global standards.
What Is AQI?
The Air Quality Index (AQI) is a numerical scale used to communicate how polluted the air currently is or is forecast to become. Instead of listing individual pollutant concentrations, AQI condenses everything into a single number from 0 to 500, with corresponding color codes and health advisories.
India’s Central Pollution Control Board (CPCB) launched the National Air Quality Index in 2014, covering eight pollutants: PM10, PM2.5, NO2, SO2, CO, O3, NH3, and Pb (lead).
How AQI Is Calculated
Each pollutant is measured separately, and a sub-index is calculated for each. The overall AQI is the highest sub-index among all monitored pollutants. This means the pollutant with the worst reading determines the final AQI value.
The calculation involves:
- Converting raw pollutant concentrations into sub-index values using breakpoint ranges
- Taking the maximum sub-index as the final AQI
- Reporting the prominent pollutant alongside the AQI value
For example, if PM2.5 is at 180 µg/m³ (sub-index 273) and NO2 is at 80 µg/m³ (sub-index 50), the AQI is 273 — driven by PM2.5.
India’s AQI Categories
| AQI Range | Category | Color |
|---|---|---|
| 0–50 | Good | Green |
| 51–100 | Satisfactory | Light Green |
| 101–200 | Moderate | Yellow |
| 201–300 | Poor | Orange |
| 301–400 | Very Poor | Red |
| 401–500 | Severe | Maroon |
Unlike the US EPA’s six-category system (0–50, 51–100, 101–150, 151–200, 201–300, 301–500), India uses a six-category system with different breakpoints. India’s “Moderate” (101–200) is broader than the US’s “Unhealthy for Sensitive Groups” (101–150) and “Unhealthy” (151–200) combined.
Key Differences: India vs US EPA
- Breakpoints: India uses different concentration-to-AQI mappings. For PM2.5, India’s “Good” threshold is 0–30 µg/m³ (24-hour), while the US EPA uses 0–12 µg/m³.
- Pollutants: India’s AQI includes NH3 and Pb; the US AQI does not.
- Reporting: Indian cities often report “emergency” or “severe plus” levels exceeding 500, which the US system caps at 500.
Why AQI Matters
AQI helps you make daily decisions: whether to wear a mask, run the air purifier, or let children play outdoors. When AQI crosses 200 (“Poor”), health impacts begin affecting the general population, not just sensitive groups.
Key Takeaways
- AQI condenses multiple pollutants into a single 0–500 number
- India’s AQI system was launched by CPCB in 2014 and covers 8 pollutants
- The highest sub-index determines the final AQI
- India’s breakpoints differ from the US EPA system — India’s “Good” allows higher PM2.5 levels
- AQI above 200 affects the general population, not just sensitive groups