Cloudy skies over Beijing? Actually, no - the gray haze you see above is pollution.
NASA's Aqua satellite captured the patch of winter haze over the mega cities of Beijing and Tianjin on January 10, 2012:
One major constituent of haze is particle pollution, such as dust, liquid drops, and soot from burning fuel or coal. Particles smaller than 10 micrometers (called PM 10) are small enough to enter the lungs, where they can cause respiratory problems. The density of PM10 reached 560 micrograms per cubic meter of air on January 10, said the Beijing Environment Protection Bureau. By contrast, U.S. cities exceed air quality standards when PM10 concentrations reach 150 micrograms per cubic meter.
But most of the pollution that makes up haze isn’t PM10; it’s finer particles, smaller than 2.5 micrometers in diameter (PM2.5). These particles can embed themselves deep in the lungs and occasionally enter the blood stream. The fine particles are highly reflective, sending sunlight back into space. The Chinese government does not currently measure PM2.5, but the U.S. Embassy in Beijing reports their measurements hourly in a Twitter feed. On the morning of January 10, PM2.5 measurements were off the scale, though by afternoon they had dropped to moderate levels. The Beijing Environmental Bureau will start releasing PM2.5 measurements sometime before January 23, the Chinese New Year.
You lungs thank you for not living there: Link