A pedestrian wears a mask at Tiananmen Square as protection from severe pollution on Thursday, January 31, 2013, in Beijing. It's the fourth time this year that a heavy blanket of smog has affected eastern China, including the capital. The air quality has reached hazardous levels, and residents were encouraged to avoid outdoor activities. <a href="index.php?page=&url=http%3A%2F%2Fedition.cnn.com%2Fvideo%2F%23%2Fvideo%2Fworld%2F2013%2F01%2F31%2Fmr-beijing-smog.cnn" target="_blank">Watch a video explaining the hazardous smog.</a>
Hazardous smog over Beijing —
A pedestrian wears a mask at Tiananmen Square as protection from severe pollution on Thursday, January 31, 2013, in Beijing. It's the fourth time this year that a heavy blanket of smog has affected eastern China, including the capital. The air quality has reached hazardous levels, and residents were encouraged to avoid outdoor activities. Watch a video explaining the hazardous smog.
Feng Li/Getty Images
Japanese tourists take photos from Jingshan Park as smog continues to shroud Beijing on January 31. The smog also forced the cancellation of airline flights and highway closures in parts of Beijing, Chinese state media reported.
Hazardous smog over Beijing —
Japanese tourists take photos from Jingshan Park as smog continues to shroud Beijing on January 31. The smog also forced the cancellation of airline flights and highway closures in parts of Beijing, Chinese state media reported.
MARK RALSTON/AFP/Getty Images
Tourists visit smog-shrouded Tiananmen Square.
Hazardous smog over Beijing —
Tourists visit smog-shrouded Tiananmen Square.
Feng Li/Getty Images
A small child wears a panda mask at Tiananmen Square.
Hazardous smog over Beijing —
A small child wears a panda mask at Tiananmen Square.
Feng Li/Getty Images
Chinese tourists look at the barely visible historic buildings in Jingshan Park.
Hazardous smog over Beijing —
Chinese tourists look at the barely visible historic buildings in Jingshan Park.
MARK RALSTON/AFP/Getty Images
A child slips on frozen pavement in Tiananmen Square.
Hazardous smog over Beijing —
A child slips on frozen pavement in Tiananmen Square.
Feng Li/Getty Images
Heavy smog reduces visibility in Jilin, China, northeast of Beijing, on Wednesday, January 30.
Hazardous smog over Beijing —
Heavy smog reduces visibility in Jilin, China, northeast of Beijing, on Wednesday, January 30.
STRINGER/AFP/Getty Images
Residential buildings and cars can be made out through the smog in Beijing on January 30.
Hazardous smog over Beijing —
Residential buildings and cars can be made out through the smog in Beijing on January 30.
Feng Li/Getty Images
Skyscrapers in Beijing can be seen through severe smog on January 30.
Hazardous smog over Beijing —
Skyscrapers in Beijing can be seen through severe smog on January 30.
Feng Li/Getty Images
The pollution forces residents of Beijing to wear masks as they ride the bus on January 30.
Hazardous smog over Beijing —
The pollution forces residents of Beijing to wear masks as they ride the bus on January 30.
Feng Li/Getty Images
A man wearing a mask rides a bicycle as hazardous smog blankets Beijing on Tuesday, January 29.
Hazardous smog over Beijing —
A man wearing a mask rides a bicycle as hazardous smog blankets Beijing on Tuesday, January 29.
Feng Li/Getty Images
Beijing residents wear masks as they ride through the pollution on January 29.
Hazardous smog over Beijing —
Beijing residents wear masks as they ride through the pollution on January 29.
Feng Li/Getty Images
A little girl wears a cartoon mask on January 29 at Tiananmen Square to protect herself from pollution.
Hazardous smog over Beijing —
A little girl wears a cartoon mask on January 29 at Tiananmen Square to protect herself from pollution.
Feng Li/Getty Images
Beijing residents walk by the Bird Nest in Olympic Park on January 29.
Hazardous smog over Beijing —
Beijing residents walk by the Bird Nest in Olympic Park on January 29.
Lintao Zhang/Getty Images
Cars travel through the smog on Wednesday, January 23, when the pollution hit serious levels.
Hazardous smog over Beijing —
Cars travel through the smog on Wednesday, January 23, when the pollution hit serious levels.
Lintao Zhang/Getty Images
A tourist and her daughter visit Tiananmen Square during dangerous levels of air pollution on January 23.
Hazardous smog over Beijing —
A tourist and her daughter visit Tiananmen Square during dangerous levels of air pollution on January 23.
Feng Li/Getty Images
A man walks through trees on January 23.
Hazardous smog over Beijing —
A man walks through trees on January 23.
Feng Li/Getty Images
People ride the Beijing subway on January 23.
Hazardous smog over Beijing —
People ride the Beijing subway on January 23.
Feng Li/Getty Images
A video screen in Tiananmen Square shows blue skies amid the heavy smog on January 23.
Hazardous smog over Beijing —
A video screen in Tiananmen Square shows blue skies amid the heavy smog on January 23.
Feng Li/Getty Images
A woman wears a mask and rides her bike on January 23.
Hazardous smog over Beijing —
A woman wears a mask and rides her bike on January 23.
Feng Li/Getty Images
Forbidden City disappears in the fog on Wednesday, January 16.
Hazardous smog over Beijing —
Forbidden City disappears in the fog on Wednesday, January 16.
Feng Li/Getty Images
Air pollution hangs over the skyline as the sun rises over the central business district in Beijing on Monday, January 14.
Hazardous smog over Beijing —
Air pollution hangs over the skyline as the sun rises over the central business district in Beijing on Monday, January 14.
MARK RALSTON/AFP/Getty Images
Nurses attend to a baby in the hospital for the flu in Beijing on Sunday, January 13. A Beijing pediatric hospital says it has treated a record 9,000 children this month for respiratory illnesses, most of which doctors and patients blame on the smog, Xinhua reported.
Hazardous smog over Beijing —
Nurses attend to a baby in the hospital for the flu in Beijing on Sunday, January 13. A Beijing pediatric hospital says it has treated a record 9,000 children this month for respiratory illnesses, most of which doctors and patients blame on the smog, Xinhua reported.
STRINGER/AFP/Getty Images
A row of intravenous drips are prepared for parents taking their kids to the hospital for flu treatment on January 13.
Hazardous smog over Beijing —
A row of intravenous drips are prepared for parents taking their kids to the hospital for flu treatment on January 13.
STRINGER/AFP/Getty Images
Pedestrians cross a street on January 13.
Hazardous smog over Beijing —
Pedestrians cross a street on January 13.
Ed Jones/AFP/Getty Images
The sunlight reflects off a building in Beijing on Saturday, January 12.
Hazardous smog over Beijing —
The sunlight reflects off a building in Beijing on Saturday, January 12.
WANG ZHAO/AFP/Getty Images