People made a fire in New Delhi to keep warm on Friday, one of many sources of pollution that makes the city’s air among the world’s worst.

“It’s always puzzled me that the focus is always on China and not India,” said Dr. Angel Hsu, director of the environmental performance measurement program at the Yale Center for Environmental Law and Policy. “China has realized that it can’t hide behind its usual opacity, whereas India gets no pressure to release better data. So there simply isn’t good public data on India like there is for China.”

Experts have long known that India’s air is among the worst in the world. A recent analysis by Yale researchers found that seven of the 10 countries with the worst air pollution exposures are in South Asia. And evidence is mounting that Indians pay a higher price for air pollution than almost anyone. A recent study showed that Indians have the world’s weakest lungs, with far less capacity than Chinese lungs. Researchers are beginning to suspect that India’s unusual mix of polluted air, poor sanitation and contaminated water may make the country among the most dangerous in the world for lungs.

Sami Siva for The New York Times nytimes.com