Delhi, India, which is experiencing some of the worst air pollution it has ever seen. Very fine particulate matter, known as PM2.5—for the particle size in microns—is the most dangerous part from a health perspective, able to penetrate deep into the lungs, and even move into the bloodstream. The World Health Organization guideline for PM2.5 is 25 micrograms per cubic meter over the short term. Delhi has been experiencing levels over 1000 micrograms.

Pollution at this level is impossible to ignore. The acrid smog burned my eyes the whole time I was there, visibility was no more than a city block, and the sun was a pale orange disk in the sky.

The world has seen similar pollution in other cities, most notably Beijing. But the problem in Delhi has different roots than that in Beijing, and is proving more difficult to solve. Beijing’s pollution is primarily due to industrial sources—vehicles, construction, and power plants, both in the city and in nearby provinces. These sources are an important part of Delhi’s problem too, but burning of crop residues in Punjab and Haryana, dust from the desert in Rajasthan, and even fireworks from the recent Diwali festival add to Delhi’s pollution woes.

Read the full article on Dehli by Samantha Gross at Brookings