What is AQI (Air Quality Index)?
The Air Quality Index (AQI) is a single number, from 0 to 500, that tells you how clean or polluted the air is and what it means for your health. Instead of quoting raw concentrations of half a dozen pollutants, the index rolls them into one value with a colour and a category, so anyone can understand it at a glance.
India's AQI, defined by the Central Pollution Control Board (CPCB), is built from up to eight pollutants: fine particulate matter (PM2.5), coarse particulate matter (PM10), nitrogen dioxide (NO₂), ground-level ozone (O₃), carbon monoxide (CO), sulphur dioxide (SO₂), ammonia (NH₃) and lead (Pb). Each pollutant's concentration is converted into a sub-index using standard breakpoints, and the overall AQI is the highest of those sub-indices — so the index always reflects the worst pollutant, known as the "dominant" or "prominent" pollutant.
The six AQI categories
| AQI | Category | Associated health impact |
|---|---|---|
| 0–50 | Good | Air quality is considered satisfactory and air pollution poses little or no risk. |
| 51–100 | Satisfactory | Acceptable air quality; minor breathing discomfort possible for unusually sensitive people. |
| 101–200 | Moderate | May cause breathing discomfort to people with lung disease such as asthma, and to children and older adults. |
| 201–300 | Poor | May cause breathing discomfort to most people on prolonged exposure. |
| 301–400 | Very Poor | May cause respiratory illness on prolonged exposure; effects more pronounced for people with lung and heart disease. |
| 401–500 | Severe | Affects healthy people and seriously impacts those with existing diseases; avoid outdoor activity. |
Why the AQI matters
Air pollution is linked to asthma, reduced lung function, heart disease and other conditions, and the risk rises with both the level and the length of exposure. The AQI helps you make everyday decisions — when to exercise outdoors, whether a child's sports practice should move indoors, when to wear an N95 mask, and when to close windows and switch on an air purifier. Sensitive groups — children, older adults, pregnant people and anyone with respiratory or heart conditions — should act at lower AQI levels than the general population.
Because pollution changes hour to hour and season to season, checking a live reading is far more useful than relying on a general impression. See the live AQI for your city →
Frequently asked questions
What is a good AQI?
An AQI of 0–50 is "Good" and 51–100 is "Satisfactory". Below 100 the air poses little risk to most people.
What is a dangerous AQI level?
AQI above 300 ("Very Poor") affects everyone, and above 400 ("Severe") is hazardous — outdoor activity should be avoided.
What does AQI stand for?
AQI stands for Air Quality Index — a 0–500 scale summarising air pollution and its health impact.