A number of Chinese cities, including Beijing, are currently experiencing the worst episode of air quality in recent memory. Residents have been told to stay inside, and the Chinese government ordered factories to scale back on their emissions. Hospitals have been busy, experiencing a 20 to 30 percent increase in patients complaining of respiratory issues. NASA recently released a hi-res photo showing the scale of the pollution as seen from space.
Taken on January 14 by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite, the image shows extensive haze, low clouds, and fog over the region.
According to NASA, the gray and yellow tinges amidst the bright clouds are indicative of the pollution. In the cloud-free areas, globs of gray and brown smog can be seen obscuring the cities below.
For comparison, NASA has provided an image of the area taken on January 3 (below). It also has an image comparison tool available here.
In terms of the air quality itself, NASA writes:
Also at the time of the image, the air quality index (AQI) in Beijing was 341. An AQI above 300 is considered hazardous to all humans, not just those with heart or lung ailments. AQI below 50 is considered good. On January 12, the peak of the current air crisis, AQI was 775 the U.S Embassy Beijing Air Quality Monitor-off the U.S. Environmental Protection Agency scale-and PM2.5 was 886 micrograms per cubic meter.