Vehicles run on a fog shrouded road in Jinan, capital of east China's Shandong Province, Dec. 6, 2011. Many areas in China witnessed heavy fog on Tuesday. The visibility in some areas were less than 200 meters. China's National Meteorological Center (NMC) has issued a yellow alarm against fog. (Xinhua)

　　BEIJING, Dec. 6 (Xinhua) -- The ongoing foggy weather and decreasing air quality that have shrouded parts of China since Sunday has prompted a surge in mask sales and affected the vegetable supply by crippling traffic and closing expressways.

　　According to statistics from Taobao Mall, China's largest online marketplace, more than 30,000 masks were sold on Sunday, more than 20,000 of which were bought by customers from Beijing.

　　The Beijing Meteorological Center on Sunday afternoon issued a yellow alert, the second-lowest level in the country's weather warning system, to warn about fog and smog in the capital, saying visibility would drop to less than 500 meters in most parts of the city.

　　The city's air pollution index (API) was between 150 and 170 on Monday.

　　Beyond masks, residents in many major cities are facing rising vegetable prices as the smog has closed expressways heading to Shouguang, the country's largest vegetable production base, located in Shandong province, where about 10 expressways have been forced to shut down, local authorities said.

　　The delays and difficulties in transporting vegetables shortens the preservation period, which in turn contributes to higher prices, said Zhang Yanxiang, chairman with the Yanxiang Organic Vegetable Ltd.

　　Visibility was reduced to less than 1,000 meters in north, central and east China, and less than 200 meters in a few areas, the National Meteorological Center (NMC) reported Tuesday.

　　As of 2 p.m. Monday, 207 inbound and outbound flights were canceled at Beijing Capital International Airport.

　　Scattered snow fall Tuesday morning has prolonged the fog and low visibility in Beijing.

　　In an effort to combat the smog and aid traffic, Beijing has increased lighting on roads.

　　Authorities with the Beijing Electric Power Corporation said they will initiate an emergency response lighting plan based on visibility standards.