Question 1

What is AQI?

Accepted Answer

The Air Quality Index turns pollutant concentrations into one number from 0 to 500: higher means dirtier air and bigger health effects. It is computed from PM2.5, PM10, ozone and nitrogen dioxide — whichever is worst sets the number.

Question 2

Why do India and US numbers differ for the same air?

Accepted Answer

India’s NAQI (CPCB) and the US EPA index use different breakpoints and band names. For example, PM2.5 of 60 µg/m³ reads ~100 (Satisfactory) on the Indian scale but ~154 (Unhealthy) on the US scale. Both are computed from the same air — they just slice it differently.

Question 3

Is this measured or modeled data?

Accepted Answer

Modeled. v1 uses the CAMS atmospheric model via Open-Meteo — a physics simulation of the atmosphere, not a physical monitor next to you. Station-level measured data is planned for v2.

Question 4

What is PM2.5?

Accepted Answer

Fine particles smaller than 2.5 micrometres — about 30 times thinner than a human hair. They come from vehicles, industry, burning and dust, and are small enough to enter the bloodstream, which is why they drive most health damage.

Question 5

When is air quality worst?

Accepted Answer

Winter, roughly October to January: cold air traps pollution close to the ground, and calm winds let it build up day after day. In North India, stubble burning adds a sharp seasonal spike. On severe winter days PM2.5 in the worst-hit cities can cross 300 µg/m³ — Hazardous on the US scale. In the San Francisco Bay Area, late-summer and autumn wildfire smoke is the other big driver — a single fire can push AQI into Hazardous overnight.

Question 6

How many years of life does air pollution cost?

Accepted Answer

If Delhi’s air permanently met the WHO guideline, the average resident would live 8.2 years longer, according to the University of Chicago’s Air Quality Life Index (2025, using 2023 data). The average Indian would gain 3.5 years. These are population counterfactuals, not individual predictions.

Question 7

How many people die from air pollution each year?

Accepted Answer

About 7.9 million in 2023 — roughly 1 in 8 deaths worldwide — making air pollution the second-biggest killer after high blood pressure (State of Global Air 2025, HEI + IHME). In India alone it was ~2 million deaths in 2023.

Question 8

Is air pollution worse for children?

Accepted Answer

Yes. Children breathe faster, spend more time outdoors, and their lungs are still growing — a long-running USC study found children’s lungs literally grow bigger when air gets cleaner.

San Francisco

Can kids play outside today?

Why air quality matters

Air composition

Next 24 hours

5-day outlook

Pollen

UV index

Why we’re different

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