to burn(I suspect the hi pollution in bharat has lots to do with burning of bio-mass like grass, firewood,dung(undigested grass)

PM2.5 level in 'green delhi' is 153.Beijing's = 56; NY's = 14

http://money.cnn.com/2015/04/14/news/economy/india-delhi-air-pollution/

In 2014, the World Health Organization measured air quality levels in 1,600 cities around the world, and the Indian capital city of New Delhi was found to have the highest concentration of particulate matter smaller than 2.5 micrometers, also called PM2.5.

The city's average PM2.5 level was a whopping 153, compared to 14 in New York and 56 in Beijing. The WHO's safety threshold for humans is 10. PM2.5 particles are not visible, but they go deep into the lungs, and are more likely to cause chronic health problems.

"Delhi is a very green city," said Kamal Meattle, a Delhi-based air pollution activist. "But even the greenest areas of Delhi have extreme pollution levels."