"NEW DELHI - Air pollution in New Delhi and surrounding towns reached the worst levels so far this year on Sunday, with authorities in the world’s most polluted capital city having already declared a public health emergency and ordered the closure of schools.
The air quality index, measuring levels of PM 2.5, tiny particulate matter in the air, deteriorated to above 900, way over the 500-level that qualifies as “severe-plus”.
Aside from the harm it was doing to the lungs of some 40 million people living in the capital region, the smog was so bad more than 30 flights were diverted from Delhi airport due to poor visibility."
Source: Reuters, 11/04/2019