China's smog problem

People ride along a street on a smoggy day in Daqing, Heilongjiang province Oct. 21, 2013.

Chinese aviation authorities will soon require captains of domestic flights into Beijing to master low-visibility landings to combat chronic flight delays that have been worsened by heavy smog.

Thick smog has canceled or delayed flights at the Beijing airport when the city's visibility goes down to a few hundred yards - though officials typically blame the delays on weather conditions rather than pollution.

Shanghai

A man wears a mask while walking on a bridge during a hazy night in Shanghai's financial district of Pudong Dec. 5, 2013.

Hazardous air pollution forced schools to shut or suspend outdoor activities in at least two cities in eastern China, where residents complained of the yellow skies and foul smells that are symptomatic of the country's crippling smog crisis.

Nanjing suspended classes in primary and secondary schools and Qingdao banned outdoor activities, said the official Xinhua news agency.

Beijing

The air pollution levels in the sky over Tiananmen Square during the National People's Congress in Beijing are seen in this combination picture taken on the dates, from left, March 6, 7, 8, 9, 10, 11, 12, 14 and 15 in 2013.

Chinese Premier Li Keqiang pledged on March 17, 2013, that his government would "show even greater resolve" in tackling China's festering pollution crisis, a source of increasing public fury. Air quality in Beijing has mostly stayed above "very unhealthy" and "hazardous" levels since the beginning of 2013.

Beijing

A woman wearing a mask rides her bicycle along a street on a hazy morning in Beijing Feb. 28, 2013.

Harbin

A traffic policeman signals to drivers during a smoggy day in Harbin, Heilongjiang province, Oct. 21, 2013. The second day of heavy smog forced the closure of schools and highways with a "particulate matter," or PM, 2.5 index exceeding 500 micrograms per cubic meter in downtown Harbin, according to the official Xinhua news agency.

Xinjiang

A residential compound is seen during a smoggy day in Wujiaqu, Xinjiang Uighur autonomous region, Nov. 19, 2013.

Beijing

People walk through a pedestrian bridge on a heavy haze day in Beijing Jan. 12, 2013.

Air quality in Beijing was the "worst on record" according to environmentalists as the city's pollution monitoring center warned residents to stay indoors with pollution 30-45 times above recommended safety levels.

Jinan

Students do body exercise during a class break on a foggy day in Jinan, Shandong province, Jan. 14, 2013. Heavy fog enveloped a large swath of east and central China with the city's residents being advised to stay indoors to avoid the heavily polluted air, the official Xinhua news agency reported.

Shanghai

The financial district of Pudong is seen on a hazy day in Shanghai Jan. 21, 2013.

Shanghai

A group of expatriates distribute face masks to pedestrians to raise awareness about air pollution in downtown Shanghai Jan. 24, 2013. According to the U.S. Consulate, air quality readings, which measure PM 2.5 particulates, Shanghai's air quality was "very unhealthy."

Shanghai

A group of expatriates distribute face masks to pedestrians to raise awareness of air pollution in downtown Shanghai, Jan. 24, 2013.

Jiaozuo

People practise Taiji on a foggy day at a park in Jiaozuo, central China's Henan province, Jan. 28, 2013. China issued a blue-code alert as foggy weather cut visibility and worsened air pollution in some central and eastern Chinese cities, the official Xinhua news agency reported.

Beijing

Cars drive through Guomao bridge on a heavy hazy day during winter in Beijing's central business district Jan. 30, 2013.

Beijing temporarily shut down 103 heavily polluting factories and took 30 percent of government vehicles off roads to combat dangerously high air pollution, state media reported, but the city's air remained hazardous despite the measures.

Beijing

Employees of Chinese multimillionaire Chen Guangbiao's company give away cans of fresh air to a man near a street on a hazy day in central Beijing Jan. 30, 2013.

China's foulest fortnight for air pollution in memory has rekindled a tongue-in-cheek campaign by a Chinese multimillionaire with a streak of showmanship who is raising the alarm by selling canned fresh air.

Chen Guangbiao, who made his fortune in the recycling business and is a high-profile philanthropist, handed out soda-size cans of air, purportedly from far-flung and pristine regions of China, from Xinjiang in the far northwest to Taiwan off China's southeast coast.

Beijing

A Chinese national flag flies in front of the Beijing Telegraph Building on a hazy morning in central Beijing Feb. 28, 2013.

Shaoxing

A man rows a boat on a river during a hazy morning in Shaoxing, Zhejiang province, June 16, 2013.

Shenyang

A statue of China's late Chairman Mao Zedong is seen on a smoggy day in Shenyang, Liaoning province, Oct. 21, 2013.

Jilin

People walk through a square during a smoggy day in Jilin, Jilin province, Oct. 21, 2013.

Changchun

A woman walks along a street during a smoggy day in Changchun, Jilin province, Oct. 22, 2013. The severe smog continued to shroud major cities in northeast China, including Changchun, with its average visibility less than 16 feet at 6 a.m., according to local media.