A thick yellow-grey haze covering several provinces in China over the weekend and Monday had officials telling residents they should remain inside. Those venturing outdoors are seen in photographs wearing masks over their nose and mouth.
Just what caused this smog? According to China's news agency Xinhua, it's the result of burning straw. The smog continued in the provinces of Hunan, Hubei, Anhui, Jiangxi and Jiangsu through Tuesday. Xinhua reports experts in the Hubei province saying this is the worst air pollution they've seen in 10 years.
China Daily has several photos of the unusual haze:
Here's more from Xinhua on what caused the haze:
Tian Yiping, a senior researcher with the provincial environmental monitoring center said inhalable particles rose sharply from 2 a.m. Monday, but concentrations of sulfur dioxide and nitrogen dioxide remained normal.
This proves that the pollution stemmed from the burning of organic matter, not industrial accidents, said Tian.
An expert with Changsha's environmental protection bureau said fog formed after continuous downpours increased humidity in central China, and the situation worsened as farmers in north China burned wheat straw left behind in their fields after harvesting.
According to the meteorological satellite data released by the Ministry of Environmental Protection on Monday, smoke arose in Henan, Anhui and Shandong provinces, major wheat-growing provinces.
"The smoke, carried southward by northerly winds, mixed with the fog in central China, triggered the unusually-colored haze," said the expert.
Xinhua also reports two men were detained for spreading rumors that the smog was from from a chemical furnace blast.
AFP (via PhysOrg) reports resident Li Yunzhong saying he could "not believe [his] eyes" when he first saw the smog. He expressed that many were very worried as they did not know what it was.
Straw burning is banned by many local governments in the provinces, but the practice still reportedly occurs none the less. Li also is reported by AFP as saying he is skeptical burning of farmland being the cause of the smog:
"I doubt that," he said. "We don't practise large-scale shifting agriculture in our region."
Some may find the timing of this smog a bit ironic as just last week Chinese officials told the United States to stop publicizing the country's pollution levels on Twitter.
Only the Chinese government is authorized to monitor and publish air quality information and data from other sources may not be standardized or rigorous, Wu Xiaoqing, a vice environmental minister, told reporters.
In Washington, State Department spokesman Mark Toner said the U.S. had no plans to stop providing the service.
"You know, air pollution, quite frankly, is a problem in many cities and regions in China," he told a news briefing.
The Beijing government only began reporting PM2.5 earlier this year after long-standing public and international criticism of its lack of transparency about its air quality.
The government appears frustrated that there are now dueling readings for air quality and that the U.S. readings underscore the fact that pollution levels considered unhealthy in the U.S. are classified as good by China.
Wu said it isn't fair to judge Chinese air by American standards because China is a developing country and noted that U.S. environmental guidelines have become more stringent over time.
The Associated Press contributed to this report.