Smoggy fog envelops China

A Chinese man covers his nose and mouth as he walks on the street during a day of heavy pollution in Harbin in northeast China's Heilongjiang province, Oct. 21, 2013.

Visibility shrank to less than half a football field and small-particle pollution soared to a record 40 times higher than an international safety standard in the northern Chinese city as the region entered its high-smog season.

Read more: China air pollution season kicks off with a cough and wheeze as coal plants turn on for the winter

A woman walks along a road as heavy fog engulfs the city in Harbin, China, Oct. 21, 2013. Heavy fog has been lingering in northeast China since Monday, disturbing the traffic, worsening air pollution and forcing the closure of schools.

A man wearing a mask walks along a road as heavy fog engulfs the city in Harbin, China, Oct. 21, 2013.

Cyclists ride along a road as heavy fog engulfs the city in Daqing, China, Oct. 21, 2013.

Pedestrains walk along a road as heavy fog engulfs the city in Harbin, China, Oct. 21, 2013.

A woman wearing a mask walks with a man past a decoration for the China National Tourism Campaign with a slogan "Beautiful China" on display along the Chang'an Avenue in Beijing, Oct. 21, 2013.

A woman wearing a mask walks through a street covered by dense smog in Harbin, northern China, Oct. 21, 2013.

A man pushes a bike onto a bridge during a day of heavy pollution in Harbin in northeast China's Heilongjiang province, Oct. 21, 2013.

A woman uses a smart phone to take a souvenir photo near a decoration for the China National Tourism Campaign with a slogan "Beautiful China" on display along Chang'an Avenue in Beijing, Oct. 21, 2013.

Chinese men walk on the street during a day of heavy pollution in Harbin in northeast China's Heilongjiang province, Oct. 21, 2013.

Two women cover their mouths and noses with a jacket as they cross a street covered by dense smog in Harbin, northern China, Oct. 21, 2013.

A Chinese woman wears a mask as she takes part in communal dancing during a day of heavy pollution in Harbin in northeast China's Heilongjiang province, Oct. 21, 2013.

A woman wearing a mask walks past a decoration for the China National Tourism Campaign with a slogan "Beautiful China" on display along Chang'an Avenue in Beijing, Oct. 21, 2013.