Fine particulate matter pollution led to the premature deaths of nearly 15,000 people in New Delhi in 2016, according to a new study by researchers from Thailand, Singapore and the Indian Institute of Technology, Bombay. The study will be published in Elsevier’s Process Safety and Environmental Protection journal.

The researchers studied deaths caused by pollution in 13 Asian cities, and found that 14,800 people died in Delhi due to PM 2.5. PM, or particulate matter, is a fine mixture of solids and liquid droplets in the air, and PM 2.5 is a category of pollutants that are less than 2.5 micrometres in diameter.

PM 2.5 pollutants are small enough to lodge themselves into human lungs. Several diseases such as strokes, lung cancer and upper respiratory tract illnesses are related to particulate matter exposure.

Delhi was surpassed only by Beijing and Shanghai, where 18,200 and 17,600 premature deaths related to PM 2.5 were reported, respectively. Among the other Indian cities studied, 10,500 people died prematurely in Mumbai due to their exposure to PM 2.5 in 2016. In Kolkata, 7,300 such deaths were reported, and Bangalore and Chennai saw 4,800 such deaths each in 2016.

The other cities that were surveyed include Chongqing (10,400 deaths), Tianjin (9,800), Guangzhou (7,600) and Shenzhen (6,400) in China. In Bangladesh’s Dhaka, about 9,100 people died prematurely due to pollution caused by particulate matter in 2016. In Pakistan’s Karachi, there were 7,700 such deaths, the study estimated.

“Chinese cities report higher mortality numbers, despite lower pollution levels than cities like Delhi because the population in their cities is more,” Kamal Jyoti Maji, a co-author of the paper, told the Hindustan Times. “Also there is a higher burden of elderly people who are disproportionately affected by air pollution exposure.”

The study also highlights the need for urgency in setting up “decisive air quality targets by megacity authorities” and advocates for joint regional efforts to control air pollution.