“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.

India has the world’s highest death rate because of chronic respiratory diseases, and it has more deaths from asthma than any other nation, according to the World Health Organization. A recent study found that half of all visits to doctors in India are for respiratory problems, according to Sundeep Salvi, director of the Chest Research Foundation in Pune.

Clean Air Asia, an advocacy group, found that another common measure of pollution known as PM10, for particulate matter less than 10 micrometers in diameter, averaged 117 in Beijing in a six-month period in 2011. In New Delhi, the Center for Science and Environment used government data and found that an average measure of PM10 in 2011 was 281, nearly two-and-a-half times higher.