Understanding Air Quality Index

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November 10, 2017

Why in news?

  • National capital region smog pollution reaches hazardous levels.
  • It is time to know about mechanism of air quality index

What the Air Quality Index (AQI)?

  • AQI is a number used to communicate to the public how polluted the air currently is or how polluted it is forecasted to become.
  • As AQI increases, an increasingly large percentage of the population is likely to experience increasingly adverse health effects.
  • Different countries have their own air quality indexes, corresponding to different national air quality standards.
  • The AQI is most commonly used to describe ground-level ozone levels. 
  • However, the AQI can be used to represent five pollutants that pose a threat to human health. 
  • These pollutants are:
  1. Ground-level Ozone or O3
  2. Particulate Matter (soot and dust) or PM
  3. Carbon Monoxide or CO
  4. Sulphur Dioxide or SO2 and
  5. Nitrogen Dioxide or NO2

How it is calculated?

  • The pollutants in the affected air are given a weight based on a formula.
  • That weight depends on the kind of impact it has on human health, each of the pollutants is given a weight.
  • The worst of these weights is given as a composite air quality.
  • So instead of giving six different numbers, six different colours, it throws up one single colour, one single number.
  • The index will throw up one number which will be given to the public.
  • People will know the health of their air quality based on this number and one associated colour code.


Level of Health Concern

AQI Values



0 to 50



51 to 100


Unhealthy for sensitive groups

101 to 150



151 to 200


Very Unhealthy

201 to 300



301 to 500


Source: Indian Express

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