Air Quality Index (What is it?)
- The Air Quality Index (AQI) is a numerical indicator used to communicate the overall quality of ambient air and its potential impact on human health.
- India’s National Air Quality Index (NAQI) was launched in October 2014 under the Swachh Bharat Mission.
- It was developed by the Central Pollution Control Board (CPCB), under the Ministry of Environment, Forest and Climate Change (MoEFCC).
- It converts complex air pollution data into a single number, colour and associated health advisory.
Pollutants Monitored Under India’s AQI
India’s AQI considers eight major air pollutants:
- PM2.5 – Particulate Matter (diameter ≤2.5 micrometres).
- PM10 – Particulate Matter (diameter ≤10 micrometres).
- NO₂ – Nitrogen Dioxide.
- SO₂ – Sulphur Dioxide.
- CO – Carbon Monoxide.
- O₃ – Ground-level Ozone.
- NH₃ – Ammonia.
- Pb – Lead.
Six Categories of India’s AQI
| AQI Range | Category | Colour |
| 0–50 | Good | Green |
| 51–100 | Satisfactory | Light Green |
| 101–200 | Moderately Polluted | Yellow |
| 201–300 | Poor | Orange |
| 301–400 | Very Poor | Red |
| 401–500 | Severe | Maroon |
How is AQI Calculated?
- Individual sub-indices are calculated for different pollutants based on their measured concentrations and prescribed breakpoints.
- The highest pollutant sub-index determines the overall AQI.
- A minimum of three pollutant measurements is required, including either PM2.5 or PM10.
- Most pollutants use 24-hour average concentrations, while CO and O₃ use eight-hour averages.
Conclusion
AQI serves as an important scientific and public communication tool for monitoring pollution, assessing health risks and guiding evidence-based air-quality management.
| This Concept has been discussed in the following article: Delhi-NCR Air Pollution: Why GRAP Alone Cannot Ensure Sustainable Air Quality |