What Delhi Breathes — Air, Explained from the Data

Every winter, Delhi's air changes. Here is why.

A calm, sourced guide to what PM2.5 and the AQI mean, where Delhi's pollution comes from, why winter is worst, and what actually helps. Every number links to the document it came from.

Delhi's air, 1 January to 31 December 2024: one thin stripe per day, coloured by CPCB AQI category. The 87 Very Poor and Severe days cluster at both ends of the year.

Why I made this

[DRAFT — Sahil to rewrite] I live in New Delhi, and every October the same argument starts again. Someone blames the farmers in Punjab, someone blames the firecrackers, someone blames the traffic, and everyone quotes a number from an app that disagrees with the number on someone else's app. I wanted one calm place that explains what those numbers mean, where the studies say the pollution comes from, and why winter is so much worse, with every claim linked to the document it came from. This site shows no live data. It is meant to help you read the live data for yourself.

— Sahil Tayal, New Delhi

A year in Delhi's air

Every square is one day of 2024, coloured by the AQI category in CPCB's daily bulletin for Delhi. There was not a single Good day. Hover over a day, or focus the calendar and use the arrow keys, to read it.

Good 0–50 0 days
Satisfactory 51–100 66 days
Moderate 101–200 143 days
Poor 201–300 70 days
Very Poor 301–400 70 days
Severe 401–500 17 days

Four days to look at

14 January 2024: Winter's lid. AQI 447, Severe, in the January cold.
28 June 2024: First monsoon rain. AQI 64 on the day the monsoon arrived; 118 the next day.
31 October 2024: Diwali. AQI 328, Very Poor, but not the year's peak.
18 November 2024: The year's worst day. AQI 494, Severe, in the stubble-season run of 13–20 November.

See every day as a table · Download the data (CSV, 366 rows)

Source: CPCB daily AQI bulletins, 1 January to 31 December 2024, 4 pm values averaging the previous 24 hours. All 366 days present; no missing days. How the data was extracted.

Chapters

Each chapter stands on its own; read them in any order.

1What is PM2.5, and what else is in Delhi's air?
PM2.5, PM10 and the gases, drawn to scale against a human hair.
2How do you read India's AQI?
The six categories, the breakpoints, the ‘worst pollutant wins’ rule, and Indian versus US numbers.
3Where does Delhi's pollution come from?
Two landmark source studies side by side, and why their numbers differ.
4Why is Delhi's air worse in winter?
Inversions, the plain, stubble and Diwali, checked against the 2024 data.
5What does the government do? GRAP, CAQM and NCAP
GRAP's four stages, the commission behind them, and the national programme.
6What does air pollution do to health?
The big estimates for India and Delhi, with their uncertainty and methods.
7What actually helps at home?
Masks, purifiers, CADR and windows: what the studies measured.
8Which Delhi air myths don't hold up?
Houseplants, smog towers, ‘only stubble’ and rain.
9How do you read Delhi's live air data yourself?
The official portals and apps, and how to pick your station.

Last reviewed 24 October 2026. How this was made · Sources & further reading