What is AQI? Full form, meaning and the CPCB scale
AQI full form
AQI stands for Air Quality Index. It turns the levels of several air pollutants into one number from 0 to 500, so you can tell at a glance how clean or polluted the air is. The higher the number, the worse the air.
How India calculates AQI
India uses the National Air Quality Index, published by the Central Pollution Control Board (CPCB) since 2014. It looks at up to eight pollutants: PM2.5, PM10, nitrogen dioxide (NO₂), sulphur dioxide (SO₂), carbon monoxide (CO), ozone (O₃), ammonia (NH₃) and lead (Pb).
Each pollutant gets its own score, called a sub-index. The AQI is the highest of these sub-indices, and that pollutant is called the main (prominent) pollutant. At least three pollutants must be measured, and one of them must be PM2.5 or PM10.
Most pollutants are averaged over 24 hours, and carbon monoxide and ozone over 8 hours. That is why the AQI changes gradually rather than minute by minute.
The CPCB AQI scale
India uses the CPCB National AQI. Apps using the US scale show different numbers.
Minimal impact
Minor breathing discomfort to sensitive people
Breathing discomfort to people with lung, asthma and heart diseases
Breathing discomfort to most people on prolonged exposure
Respiratory illness on prolonged exposure
Affects healthy people and seriously impacts those with existing diseases
PM2.5 and PM10
PM2.5 and PM10 are tiny particles of dust, smoke and soot, smaller than 2.5 and 10 micrometres across. PM2.5 is fine enough to travel deep into the lungs. In most Indian cities in winter, PM2.5 is the main pollutant.
Why other apps show different numbers
Many international apps use the US EPA AQI, which has different cut-off points, especially for PM2.5. The same air often gets a higher number on the US scale. Government orders in India, such as GRAP, and Indian news reports use the CPCB scale, which is what this site shows.
Why AQI gets worse in winter
From October to January, cooler air and calm winds trap pollution close to the ground. Smoke from farm fires, festival firecrackers, vehicle exhaust, construction dust and waste burning add to it. This is why Delhi NCR often reaches Very Poor or Severe in November.
Common questions
What is the full form of AQI?
AQI stands for Air Quality Index.
What is a good AQI?
On the CPCB scale, 0–50 is Good and 51–100 is Satisfactory. Above 200 is Poor.
What AQI level is dangerous?
Above 300 (Very Poor) can cause breathing illness with long exposure. Above 400 (Severe) affects even healthy people.
How do I check the AQI at my location?
Use the "Use my location" button on the home page, or search for your city or area.