The city government reported an air quality index score of 500 for a second consecutive day on Tuesday, the highest possible reading offered in China. The real number was likely much higher at times.

By way of comparison, New York City had a reading of less than 50 on Tuesday. The U.S. government categorizes any score over 300 as "hazardous."

It is notoriously difficult to get accurate pollution readings in China. When severe smog hits Beijing, residents rely on the U.S. Embassy's own readings published via social media.