BEIJING, June 12 (Xinhua) -- Grey haze was reported over a vast portion of central China on Tuesday, and is believed to have been caused by farmers burning straw.
According to local environmental protection authorities, lingering haze has shrouded Hunan, Hubei, Anhui, Jiangxi and Jiangsu provinces since Monday.
Hubei province witnessed the worst foggy weather in 10 years in coverage, density, as well as duration, experts believe.
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.
Two men in the provincial capital of Wuhan were detained Tuesday after spreading rumors on the Internet, claiming that a chemical furnace blast and chlorine leakage had caused the gray-yellow fog.
The rumors spread across the Internet, triggering public panic in the city, police said.
Five highways in the northern part of neighboring Anhui province were closed for a half-hour from 9:30 a.m. as visibility dropped to less than 20 meters in the area, according to the provincial traffic police corps.
Meanwhile, the concentration of PM10 particles in Hunan's capital Changsha reached 0.459 mg per cubic meter of air. The value was close to the city's worst air pollution record, established when the city was hit by sandstorms.
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.
Residents in Nanjing, provincial capital of Jiangsu, tracked a burning smell since fog covered the city starting Saturday.
Local governments forbid straw burning, but farmers continue to burn straw as there is no profit in recycling it and leaving it on farmland will affect the next season's crop growth.
The expert advised residents to stay indoors or wear masks outdoors.
Experts say the haze will be dispersed after the wheat harvesting season ends in north China, and southerly winds in the summer will also help break it up.