A study in The Lancet Planetary Health estimated that long-term exposure to fine particles called PM2.5 is linked to around 1.5 million extra deaths a year in India, compared with meeting the World Health Organization's air quality guideline. PM2.5 particles are small enough to reach deep into the lungs and the bloodstream.
Looking at data from 2009 to 2019, the researchers estimated that each 10 microgram per cubic meter rise in PM2.5 was tied to about an 8.6% higher death rate. For context, Delhi's yearly average has passed 100 micrograms per cubic meter, while the WHO guideline is 5 and India's standard is 40.
The figure is striking, and it has limits. These are estimated, or attributable, deaths, not counted death certificates. Scientists model how many deaths are statistically linked to pollution, so different methods produce different totals. An earlier global study put India's figure nearer 1 million, while this one estimated about 1.5 million. Because people cannot be randomly assigned to clean or dirty air, this is observational research, and factors like poverty and healthcare access could play a role. The study used a design comparing places and times to limit those issues. No single study fixes the exact number, but many agree on the direction and rough scale of a heavy health burden.