This is really bad. NASA has published an image of the pollution haze taking all over the North China Plain. Yes, it's so bad that you can see it taking over thousands of square miles from space.
Things were so bad that visibility dropped to 200 meters. The Chinese capital's airport had to cancel 43 flights and delayed 80 more.
The first image—taken by NASA's Aqua satellite—shows the situation on January 10. The entire North China Plain was covered with a gray pollution haze. You can also see white patches: that's normal fog hanging below the haze. On the second image, you can see the skies on the next day: the heaviest pollution is mostly gone, moved by the wind.
According to NASA's Earth Observatory, the haze is mostly made of two kinds of particles, PM10 and PM2.5. The number refers to their size: 10 micrometers and 2.5 micrometers. They are made of "dust, liquid drops, and soot from burning fuel or coal." Most of the pollution is made of PM2.5. These are highly reflective, which is why we can see them from space when their concentration is high enough.
The 10-micrometer particles enter the lungs and cause respiratory problems. The 2.5-micrometer particles can embed themselves deep in the lungs and occasionally enter the blood stream. These particles can cause cancer and extreme respiratory problems.
Extremely bad. The PM10 density was 560 micrograms per cubic meter of air. In the US, concentrations of 150 micrograms per cubic meter of air are considered beyond the limit.
But the PM2.5 concentration is even worse. On January 10, the concentration was literally off the scale. Things are so bad that the US Embassy in Beijing reports on the PM2.5 concentration level every hour.
Winter haze is caused by a combination of pollution and temperature inversion: cold air gets trapped by a blanket of warmer air above, causing a pocket that gets filled with pollution. In the case of China, it builds up pretty fast.
Apparently, China is planning to monitor the concentration of PM2.5 in 2016. That may be too late for much of the population, who is deeply affected by the situation. It's no coincidence that their architects are obsessed by air quality control inside their buildings. [NASA]