NEW DELHI — New Delhi’s air is the most polluted in the world, according to an international report that quantifies pollution levels, confirming findings by experts confounded by the lack of attention to the city’s problem.

The findings by the World Health Organization, released on Wednesday, show that the cities ranking second through fourth are also in India, in the central Hindi belt.

For years, experts have wondered why so much international attention has focused on air pollution in Beijing when some say conditions are as bad or even worse in South Asia.

“I am shocked at the extent of the problem they found in India,” said Dr. Sundeep Salvi, the director of the Chest Research Foundation in Pune, India. “This is incredibly bad, and there is a complete lack of awareness about it both amongst policy makers and the common man.”