A standardized index measuring air pollution levels, indicating how clean or polluted the air is and associated health risks.
air-qualityWhat is AQI?
The Air Quality Index (AQI) is a standardised number that summarises how polluted the air is on any given day. It converts complex measurements of half a dozen different pollutants into a single value that anyone can interpret — green means safe, red means dangerous. AQI is the most important air-quality concept for billions of people living in highly polluted regions like South Asia, where winter smog routinely pushes readings into hazardous territory.
AQI is calculated separately by national agencies (the CPCB in India publishes the National AQI on a 0–500 scale, the US EPA uses a 0–500 scale with slightly different breakpoints, and the European Environment Agency (EEA) uses a 0–100+ scale). Mausam Online displays the European AQI because it is computed identically on the same Open-Meteo data and provides a continuous numeric value rather than a stepped index.
How AQI is calculated
AQI takes hourly concentrations of major air pollutants, normalises each one to a sub-index, and reports the highest of the sub-indices as the overall AQI. The most influential pollutants in South Asia are:
- PM2.5 — Fine particulate matter smaller than 2.5 µm. It penetrates deep into the lungs and the bloodstream and is the single biggest contributor to premature mortality from air pollution worldwide.
- PM10 — Coarse particulate matter up to 10 µm, including dust, pollen, mould spores and construction dust.
- Ozone (O₃) — A summer-afternoon pollutant created by sunlight reacting with vehicle exhaust.
- NO₂ (nitrogen dioxide) — A by-product of vehicle and industrial combustion.
- SO₂ (sulfur dioxide) — Emitted by coal-fired power plants and refineries.
- CO (carbon monoxide) — From incomplete combustion in engines and stoves.
The AQI scale used on Mausam Online
| AQI | Level | What it means |
|---|---|---|
| 0–20 | Good | Excellent air. Outdoor activities are encouraged. |
| 20–40 | Fair | Acceptable. Unusually sensitive individuals should monitor symptoms. |
| 40–60 | Moderate | People with asthma or heart disease should reduce prolonged outdoor exertion. |
| 60–80 | Poor | Everyone should limit outdoor exercise; mask recommended outdoors. |
| 80–100 | Very Poor | Stay indoors; N95 mask if you must go out. |
| 100+ | Extremely Poor | Avoid all outdoor activity; air purifier indoors. |
AQI in South Asia
South Asia has the worst air quality in the world. According to the World Air Quality Report 2024, 11 of the world’s 12 most polluted cities are in India, Bangladesh, or Pakistan. The reasons are well documented:
- Winter temperature inversions (October–February) trap pollutants close to the ground across the Indo-Gangetic plain.
- Crop residue burning in Punjab and Haryana every October–November sends massive PM2.5 spikes drifting eastward to Delhi.
- Diwali fireworks cause short, intense particulate spikes, sometimes pushing Delhi’s AQI past 500.
- Construction dust and vehicle emissions are year-round contributors in megacities.
- Coal-fired power plants and brick kilns add a steady industrial baseline.
Notable hotspots: Delhi, Lahore, Dhaka, Kanpur, Patna, Lucknow, Ghaziabad and Karachi regularly exceed AQI 200 in winter. Lahore and Delhi have repeatedly hit AQI 500+ — into “Hazardous” territory where breathing the air for one day is comparable to smoking a pack of cigarettes.
How to protect yourself
- Check AQI daily on Mausam Online — every city page shows live PM2.5, PM10 and AQI with a health-advice line.
- Wear an N95 mask outdoors when AQI is above 100.
- Keep windows closed on bad days and use a HEPA air purifier indoors.
- Avoid outdoor exercise when AQI is poor — your lung intake increases 6-10×.
- Watch vulnerable family members: children, elderly, pregnant women and anyone with asthma, COPD or heart disease.
- Hydrate well and eat antioxidants (vitamin C, vitamin E, omega-3) to help the body cope.
Frequently asked questions
Is AQI the same in every country? No. India uses the CPCB National AQI (0–500), the US uses EPA AQI (also 0–500 but with different breakpoints), and Europe uses EEA AQI (0–100+). The thresholds and category labels differ. Mausam Online uses the European scale on every city page.
What’s a “safe” AQI? The WHO recommends annual PM2.5 averaging no more than 5 µg/m³, equivalent to a European AQI under 20. Most South Asian cities are nowhere near this. A daily AQI under 40 is realistically the cleanest most people will see.
Does PM2.5 really matter that much? Yes. The Global Burden of Disease study attributes around 1.7 million annual deaths in India alone to PM2.5 exposure. It contributes to heart disease, stroke, lung cancer, COPD, asthma and even premature birth.
Are air purifiers worth it? Yes for indoor air. A HEPA purifier rated for your room size can reduce indoor PM2.5 by 80–95%. Match the CADR (Clean Air Delivery Rate) to your room — for example, a 20 m² bedroom needs about 200 CADR.
When is AQI worst in India? November to January, especially in north India. The combination of crop burning, cold-trapped inversions, calm winds and festival fireworks pushes Delhi-NCR routinely above 300 and occasionally above 500.