Industry, including coal-fired power plants, contributes about 9 per cent.
The largest share, 27 per cent, comes from secondary particles, formed when gases released by vehicles, industry, power plants and biomass burning react in the atmosphere.
The formation of these particles is also fuelled by the vast quantities of fertiliser spread on fields around the capital, argues Jacob Koshy, author of a new book on pollution.
Ammonia released by fertilisers reacts with other pollutants to form secondary particulate matter.
“The sheer quantity of ammonia that is going into the atmosphere creates a base layer for other pollutants to react with,” said Koshy, science editor of The Hindu newspaper and author of “The Nitrogen Bomb”.
A 2024 study published in The Lancet Planetary Health, a peer-reviewed research journal, estimated that 3.8 million deaths in India between 2009 and 2019 were linked to air pollution.