Birds fly through a cloud of pollution which envelops a residential area near the Anand Vihar District of New Delhi on Jan. 8, 2016. (CHANDAN KHANNA/AFP/Getty Images)

More than 25 million people live in India's capital city, a place where industrial smokestacks, car exhaust and smoke from animal dung fires regularly foul the air. But recent years have seen a big uptick in the amount of pollution in New Delhi's air, to a level at which it is now often dangerous to breathe.

Levels of the air pollutant known as PM 2.5 -- a type of fine particulate matter that's considered one of the most damaging to human health -- reached 580 in New Delhi's Anand Vihar district earlier this week, the business news website Quartz noted, which meant that its air was the dirtiest in the world that day.

And New Delhi is just one of many crowded Indian cities facing this problem. “More than half of Indian cities today are classified as critically polluted cities even by the government,” Anumita Roychowdhury of the Delhi Center for Science and Environment said in an interview with PressTV.

Her comment "even by the government" is noteworthy because many doubt the Indian government's Air Quality Index provides a true measure of its pollution problems, thanks in part to bad equipment that can't measure particle pollution accurately.

Here's what the air quality was like Thursday morning (Eastern Time) in Anand Vihar:

(Air Quality Index)

The situation was much the same across the rest of the city, with hazardous readings in many areas and "unhealthy" being the best reported air, at Indira Gandhi International Airport.

Delhi's air pollution typically gets worse in the winter months thanks to its bowl-like topography, which traps dirty air and dust from construction sites. But on some days now it even surpasses Beijing, long home to some of the world's worst air pollution.

The U.S. Environmental Protection Agency considers overall Air Quality Index levels over 151 "unhealthy," and over 201 is classified as "very unhealthy." Anything over 301 is considered "hazardous," meaning that it would trigger health warnings of emergency conditions for an American city, which would affect its entire population.

By contrast, here's what air quality index levels looked like across the continental U.S. Thursday morning:

(Air Quality Index)

Cities from Houston to Los Angeles to Miami all reported measurements of "good" to "moderate" air, with readings of 17, 55 and 59, respectively.

Across much of Asia -- and especially China -- the index shows a sea of readings that are "unhealthy" at best:

(Air Quality Index)

Things aren't expected to get better for Delhi's air in the coming days, according to the Indian Institute of Tropical Meteorology, which since 2010 has maintained a website known as SAFAR ("System of Air Quality Forecasting and Research") to alert the public to the city's air quality issues in advance.

For the next three days, levels of PM 2.5 (and another pollutant known as PM 10) are forecast to be "poor" or "very poor." The levels of PM 10 are forecast to be well above 300, the level at which the EPA says would trigger emergency warnings in the U.S.

See more at the Air Quality Index Map.