In Harbin, snowfall provides relief, but warmer temperatures mean the reprieve is unlikely to last long

The severe air pollution blanketing Northeast China is expected to lift slightly on Friday, then return to hazardous levels over the weekend, according to the National Meteorological Center.

However, as cold air from the east moves in on Tuesday, the smog will disappear gradually, the center said.

On Wednesday morning, the concentration of PM2.5, fine particles that pose particular hazards to human health, was 300 micrograms per cubic meter in Harbin, ranking among the worst of more than 500 cities all over the country.

But the condition is much better than last Tuesday when the PM2.5 concentration was over 1,000, causing some primary and secondary schools in Harbin to close.

Residents in Liaoning and Jilin, who have been suffering severe smog since the beginning of November, also enjoyed a better day on Wednesday. The PM2.5 concentration was under 200 both in Shenyang and Changchun.

The PM2.5 concentration reached 1,400 in Shenyang on Sunday, according to the city's environmental protection bureau.

It is now common to see people wearing face masks in cities in the three provinces to guard against air pollution, and some mask makers are touting how their products can filter out particulate matter as small as PM2.5.

Zhu Lin, 35, who runs a Taobao store in Shenyang, has sold more than 1,000 specially designed masks over the past 10 days and is selling almost three times as many masks as she sold last year.

"I received the first order at the beginning of November, two weeks earlier than last year," said Zhu. "There was a sales peak on Sunday and Monday due to the severe smog."

"The customers are all anxious to get the masks as soon as possible, especially those who buy for their children," she said.

Snow that started to fall in Harbin on Sunday night helped to reduce air pollution, but that effect is not expected to last since the temperature has risen since Tuesday.

On Tuesday and Wednesday, the smog in parts of northeast China forced the airport in Harbin, Heilongjiang province, to cancel 191 inbound and outbound flights. Some highways in the area were also closed as visibility dropped to less than 500 meters.

Northeast China has had its heating on for the longest time in China, from the middle of October to May, and coal is the main fuel.

According to officials in environmental protection departments in the three provinces, the air pollution was caused by heating systems, straw burning and unfavorable weather conditions.

Heilongjiang has sent several teams to inspect the regions where straw burning is a common practice.

The departments of environmental monitoring and atmospheric control in Liaoning are on duty round the clock and Liaoning and Jilin asked the most heavily polluting industries to stop production.

Zhang Xiaomin in Dalian and Han Junhong in Changchun contributed to this story.

Contact the writers at zhouhuiying@chinadaily.com.cn