What does air pollution do to health?

The evidence that long-term exposure to fine particles shortens lives is strong; the exact size of the toll in India depends on which method you use, and the honest way to read any headline number is alongside its uncertainty range.

This chapter describes population studies. It is not medical advice. If you have symptoms, a heart or lung condition, or are pregnant, speak to a doctor about what Delhi's air means for you. The WHO's fact sheet on ambient air pollution is a reliable plain-language starting point.

What does the global evidence say?

The WHO estimates that ambient (outdoor) air pollution caused 4.2 million premature deaths worldwide in 2019, and that 89% of them were in low- and middle-income countries.¹ Its 2021 guidelines lowered the recommended PM2.5 levels to 5 µg/m³ a year and 15 µg/m³ a day.²³

How many deaths in India are linked to air pollution?

The most-cited state-level estimate comes from the India State-Level Disease Burden Initiative, published in The Lancet Planetary Health. It attributed 1.67 million deaths in India in 2019 to air pollution, with a 95% uncertainty interval of 1.42 to 1.92 million, or 17.8% of all deaths that year.⁴

Two things to notice. First, the range is wide: the lower and upper bounds differ by half a million people. Second, these are attributable deaths: modelled estimates of how many deaths are linked to the exposure, not a count of death certificates that name air pollution as a cause.

The same study shows the problem changing shape. Between 1990 and 2019 the crude death rate attributed to household air pollution fell by 64%, while the rate attributed to outdoor particulate pollution rose by 115%, with a very wide uncertainty interval of 28% to 344%.⁴

What did it find for Delhi?

Delhi had the highest average PM2.5 exposure of any state in 2019, estimated at 217.6 µg/m³ (uncertainty interval 117.9–297.3). It also had the highest per-capita economic loss from air pollution, about US$62 per person.⁴ The exposure figure is a modelled estimate of what residents breathe on average, not an average of Delhi's monitors, and it is not directly comparable with the AQI.

What is the Air Quality Life Index?

The Air Quality Life Index, from the Energy Policy Institute at the University of Chicago, expresses the same problem in years of life rather than deaths. Its 2025 India fact sheet, using 2023 data, says that bringing Delhi's PM2.5 down to the WHO guideline would add about 8.2 years to the average resident's life expectancy, the most of any Indian state or territory; meeting only India's own national standard of 40 µg/m³ would add about 4.7 years.⁵ Across India, average population-weighted PM2.5 was 41 µg/m³.⁵

Its method is different from the Global Burden of Disease approach. AQLI applies a relationship estimated from a natural experiment in China that compared groups with long-term exposure to different pollution levels: in its conversion, each additional 10 µg/m³ of PM2.5 reduces life expectancy by about 0.98 years.⁵ That is a single causal estimate from one country, applied to India's very different population and pollution mix. The fact sheet does not report uncertainty intervals for its headline numbers.⁵

How should you read these numbers?

As orders of magnitude, not as precise counts. The GBD and AQLI numbers come from different methods and answer different questions, so they should not be compared directly. What they agree on is direction and scale: long-term exposure to Delhi's level of fine particles carries a large health cost, and lowering it is expected to bring large gains.

For what individuals can reasonably do, and what the evidence says about masks and purifiers, see What actually helps at home?