Arvind Kumar, a chest surgeon at New Delhi’s Sir Ganga Ram Hospital, has a ringside view of the toll that northern India’s deteriorating air quality is taking on its residents. When he started practicing 30 years ago, some 80 to 90 per cent of his lung cancer patients were smokers, mostly men, aged typically in their 50s or 60s.  But in the past six years, half of Dr Kumar’s lung cancer patients have been non-smokers, about 40 percent of them women. Patients are younger too, with 8 percent in their 30s and 40s.

To Dr Kumar, the dramatic shift in the profiles of lung cancer patients has a clear cause: air fouled by dirty diesel exhaust fumes, construction dust, rising industrial emissions and crop burning, which has created heavy loads of harmful pollutants in the air.  Even in teenage lungs, Dr Kumar sees black deposits that would have been almost unthinkable 30 years ago. Chronic obstructive pulmonary disease — in short, severe lung conditions — is now India’s largest cause of death after heart disease.

“If these guys are having black deposits on their lungs as teens, what’s going to happen to them 20 years later?” asks Dr Kumar, who last week launched Doctors for Clean Air to raise awareness about the impact of air pollution. “It’s a silent crisis. It’s an emergency.”  The problem is most acute in India but it is not alone. The Financial Times collated Nasa satellite data of fine particulate matter (PM2.5) — a measure of air quality — and mapped it against population density data from the European Commission to develop a global overview of the number of people affected by this type of dangerous pollution.