Hazardous smog blights Beijing

China's capital city of Beijing has been swamped by off-the-charts levels of air pollution in January. A general view of the pollution covered Forbidden City on Jan. 16, 2013, in Beijing, China. Heavy smog shrouded Beijing with pollution at hazardous levels.

An image taken by NASA's Terra satellite on January 14 shows Beijing and the surrounding area smothered by a layer of extreme air pollution. — NASA

An image taken by NASA's Terra satellite on January 14 shows Beijing and the surrounding area smothered by a layer of smog. Grey and yellow-tinged clouds indicate areas suffering the most extreme levels of air pollution.

An image taken by NASA's Terra satellite of Beijing and the surrounding area on January 3. — NASA

For comparison, this January 3rd image, captured by the same NASA satellite, shows what the area looks like without the covering of smog.

A tourist wearing a mask looks on as pollution covers the Forbidden City on Jan. 16, 2013, in Beijing, China. Particles of pollution known as PM2.5 reached levels above 700 in recent days, and have remained at or above 300 for most of January. The World Health Organization considers levels above 25 to be unsafe for humans.

A tourist wearing a mask looks at the Forbidden City as pollution covers the city on Jan. 16, 2013, in Beijing, China. PM2.5 are tiny particulate matter less than 2.5 micrometers in size, or about 1/30th the average width of a human hair. They can penetrate deep into the lungs, and measuring them is considered a more accurate reflection of air quality than other methods.

A child wearing a mask walks in a park in Beijing on January 15, 2013. Public anger in China at dangerous levels of air pollution, which blanketed Beijing in acrid smog, spread as state media queried official transparency and the nation's breakneck development.

Beijing sits on a wide plain surrounded by hills. This geography conspires to keep still air hovering over the city. The result is images like this, taken on January 16, 2013, of China's iconic Forbidden City smothered by haze.

Tourists walk through the door of the Forbidden City as pollution covers the city on Jan. 16, 2013, in Beijing, China.

A general view of the pollution covered Forbidden City on Jan. 16, 2013, in Beijing, China.

Tourists walk through the door of the Forbidden City as pollution covers the city on Jan. 16, 2013, in Beijing, China.

A tourist wearing a mask phones at the Tiananmen Square during severe pollution on Jan. 13, 2013. At the time, PM2.5 levels were above 300, dramatically higher than the World Health Organization's recommendation that people stay indoors when levels reach 25.

A Chinese policeman guards at the Tiananmen Square during dangerous levels of air pollution on Jan. 13, 2013.

Air pollution hangs over the skyline as the sun rises over the central business district in Beijing on Jan. 14, 2013.

A woman wearing a face mask checks her phone during polluted weather in Beijing on Jan. 13, 2013. During the worst of the pollution, the Beijing Shijitan Hospital received 20 percent more patients than usual at its respiratory health department, Dr. Huang Aiben told the Associated Press. Most patients were coughing and sought treatment for chronic bronchitis, asthma and other respiratory illnesses, Huang said.

A man wearing a mask reads a newspaper at a subway station in Beijing on Jan. 15, 2013.

A general view shows buildings in the fog and haze at a central business district in Beijing on Jan. 14, 2013.

A Chinese man looks on in front of the the Forbidden City in Beijing on Jan. 14, 2013.

A tourist looks at the Forbidden City as pollution covers the city on Jan. 16, 2013, in Beijing, China.

A little tourist wearing a mask visits the Tiananmen Square at dangerous levels of air pollution on Jan. 13, 2013.

This picture taken on Jan. 12, 2013, shows sun light being reflected in a window of a building in Beijing.

A tourist wearing the mask visits the Tiananmen Square at dangerous levels of air pollution on Jan. 23, 2013, in Beijing, China.

A women wearing the mask rides a bicycle on the street during severe pollution on Jan. 23, 2013, in Beijing, China.

Beijing residents wearing the masks ride a motorcycle through a panda sculpture during severe pollution on Jan. 23, 2013, in Beijing, China.

A tourist and her daughter wearing the masks visit the Tiananmen Square at dangerous levels of air pollution on Jan. 23, 2013, in Beijing, China.

A men wearing the mask walks under the trees during severe pollution on Jan. 23, 2013, in Beijing, China.

A worker wearing the mask sits outside the construction site during severe pollution on Jan. 23, 2013, in Beijing, China.

A men wearing the mask takes the subway during severe pollution on Jan. 23, 2013, in Beijing, China.