What is AQI? India's Air Quality Index (0–500) Scale Fully Explained

What does an AQI of 150 or 300 mean? Understand India's Air Quality Index scale from 0 to 500, CPCB colour codes, health categories, and which pollutants are measured — explained simply.

You've probably seen the number on your weather app or a government website — "AQI: 187" — but what does it actually mean for you and your family? This article breaks down India's Air Quality Index (AQI) from scratch, in plain language.

What is the Air Quality Index (AQI)?

The Air Quality Index is a single number that summarizes how clean or polluted the air is at a given place and time. Instead of asking you to track six different pollutant concentrations in micrograms per cubic metre, the AQI converts all that data into one number with a colour and a health label.

India's AQI was launched in 2014 by the Central Pollution Control Board (CPCB), under the Ministry of Environment, Forest, and Climate Change. The guiding principle was simple: One Number — One Colour — One Description — so that any citizen could understand the air quality around them without needing a science degree.

You can check live AQI for any Indian city on the CPCB National Air Quality Index portal.

What Pollutants Go Into the AQI?

India's AQI considers eight pollutants for which short-term National Ambient Air Quality Standards (NAAQS) are prescribed. For the full legal concentration limits for each of these pollutants, see our detailed guide: NAAQS India: CPCB Limits for All 12 Pollutants.

1. PM10 — coarse particulate matter (dust, pollen)

2. PM2.5 — fine particulate matter (combustion, smog)

3. NO₂ — nitrogen dioxide (vehicles, industry)

4. SO₂ — sulphur dioxide (coal burning, power plants)

5. CO — carbon monoxide (incomplete combustion)

6. O₃ — ozone (photochemical reactions)

7. NH₃ — ammonia (agriculture, waste)

8. Pb — lead (industrial processes)

Key rule: AQI can only be calculated if at least 3 pollutants are measured, and one of them must be PM2.5 or PM10. If fewer are available, the data is considered insufficient for a valid AQI reading.

India's AQI Scale: 0 to 500 Explained

The final AQI value is determined by the worst sub-index among all measured pollutants. Here is what each range means:

AQI Range	Category	Colour	Health Impact
0 – 50	Good	🟢 Green	Minimal impact
51 – 100	Satisfactory	🟡 Light Green	Minor breathing discomfort to sensitive people
101 – 200	Moderate	🟡 Yellow	Breathing discomfort for people with lung disease, asthma, or heart disease
201 – 300	Poor	🟠 Orange	Breathing discomfort is experienced by most people on prolonged exposure
301 – 400	Very Poor	🔴 Red	Respiratory illness on prolonged exposure
401 – 500	Severe	🟣 Dark Red / Maroon	Affects healthy people; seriously impacts those with existing diseases

So if your city shows an AQI of 187, it falls in the Moderate range — meaning people with asthma, heart conditions, or lung disease should limit outdoor activity, while most healthy people can go about their day with minor precaution.

An AQI of 350 is Very Poor — everyone should reduce prolonged outdoor exertion.

How is India's AQI Different from the US EPA AQI?

Both systems use a 0–500 scale and six categories. The key difference is the health breakpoints — the pollution concentrations that map to each AQI number. India's NAAQS (set in 2009) allows higher concentrations before a category is triggered. For example, India's annual PM2.5 standard is 40 µg/m³ versus the WHO's recommended guideline of 5 µg/m³ — an eight-fold difference that reflects the gap between what's achievable and what's ideal.

How is AQI Reported in Real-Time?

India's AQI is published in real-time on the CPCB's web platform. The system:

• Pulls data automatically from continuous monitoring stations across the country, with no human intervention required

• Uses running 24-hour mean values (8-hourly for CO and O₃)

• Displays AQI on a rolling basis — so the AQI at 6 AM incorporates data from the past 24 hours

For manual monitoring stations, CPCB provides an AQI Calculator (Excel-based) where field staff can enter pollutant concentrations to derive the AQI.

Why Does AQI Matter?

The AQI is not just a health advisory tool — it also drives policy. When AQI crosses 400 in Delhi, for instance, the Graded Response Action Plan (GRAP) kicks in: construction halts, schools may close, and diesel vehicles face restrictions. The index thus directly connects air quality measurement to action.

Quick Takeaways

• AQI converts complex multi-pollutant data into a single number (0–500)

• India's CPCB launched the AQI in 2014 with 6 categories: Good → Severe

• The final AQI = the worst sub-index of all measured pollutants

• At least 3 pollutants (including PM2.5 or PM10) must be measured for a valid AQI

• Real-time AQI for all cities is available on the CPCB portal

Further Reading

On this blog:

• How is AQI Calculated? Formulas, Sub-Index Methods, and Worked Examples

• NAAQS India: CPCB Limits for All 12 Pollutants

External resources:

• CPCB National Air Quality Index — Live India Map

• WHO Ambient Air Quality and Health Fact Sheet