China's winters usually see heavy air pollution - mostly from generating heat. But the country's environmental data shows air quality this season is better than last. Central China was hit with severe smog this week - for a few days. CGTN's Liu Xinqing has more.

Choking smog everywhere. The whole city of Zhengzhou is blanketed in a new round of heavy smog, triggering red alerts for heavy air pollution. Among 22 cities and counties monitored by the provincial department of environmental protection, 18 reached the level of severe air pollution. The situation was so severe that all kindergartens and primary schools in the city were forced to suspend classes on Thursday. But the sky is starting to clear up. This is how the pagoda-shaped tower looked earlier this week. But now it is like this.

LIU XINQING ZHENGZHOU, HENAN "For days, the landmark Zhengzhou Tower behind me has been shrouded in heavy smog, but now it is seeing daylight again after a much-needed break from severe air pollution."

At a press conference, the deputy director of the Henan provincial department of environmental protection explained the reason behind the heavy smog.

JIAO FEI, DEPUTY DIRECTOR HENAN PROVINCIAL DEPARTMENT OF ENVIRONMENTAL PROTECTION "This round of air pollution was caused by the accumulation of local emissions. Starting from January 15th, the air humidity grew sharply, dragging down the height of the mixed layer of the atmosphere, causing severe pollution across the province."

LIU JUAN LOCAL RESIDENT, ZHENGZHOU "The air was really bad these days, so we stayed indoors most of the time. It's getting better today, so I am taking my kid out in the sun. But normally I tend to stay away from outdoor activities when the air quality isn't good."

DING GUANGHAN LOCAL STUDENT, ZHENGZHOU "We had heavy smog this week. It's been much worse than recently, and a red alert was issued yesterday. So I suggest people turn to green modes of transportation and take self-protection measures when traveling outside."

But the situation here in Henan province is not the worst. The Ministry of Environmental Protection released the air quality rankings for 2017 on Thursday. Among the top ten most polluted cities, only one is from Henan, while its neighbor Hebei province has six, making it the worst polluted place in this country. The pollution is causing a headache for most residents, but for a select few, it could be a great opportunity. In many appliance stores, air purifiers are in strong demand.

MENG QINGXIANG STORE MANAGER, SUNING APPLIANCES "Air purifiers sold well recently, because customer behavior is closely related to outdoor air quality. So when heavy smog set in over the past few days, the sale of air cleaning products went up."

Smog is not uncommon in central and northern China. Even after several rounds of iron fist measures against air pollution, lingering smog is still haunting many parts of the country. Liu Xinqing, CGTN, Zhengzhou, Henan province.