The Beijing-Tianjin-Hebei region is expected to see heavy air pollution through Wednesday because of unfavorable meteorological conditions, the top environmental authority said on Sunday.

　　The Ministry of Ecological Environment said the capital is likely to see moderate to heavy air pollution during the period. Some areas in Tianjin, Hebei, Shanxi, Shandong and Henan provinces will also be affected, it said.

　　Air pollution often worsens when heating systems are turned off in northern parts of the country - March 20 in Beijing this year - and most factories resume production after off-peak periods in autumn and winter, and pollutants begin to be discharged at a very high level.

　　More serious air pollution is likely to happen whenever heavy production and motor vehicle use coincide with unfavorable meteorological conditions that impede dispersal.

　　The Beijing-Tianjin-Hebei region is prone to air pollution in March because of the regular unfavorable atmospheric conditions that come along with rising temperatures, high moisture and a stable atmosphere, the ministry said.

　　According to the authority, this is the third year in a row that the Beijing-Tianjin-Hebei region has been struck in March by heavy air pollution.

　　The ministry said it has been paying close attention and providing solutions for local governments to help mitigate the effect on people's health. It also issued an orange alert for smog - its second-highest warning level - for Beijing and 33 other cities in affected areas.

　　The Beijing Municipal Environmental Protection Bureau said it has been taking measures since March in response to the seasonal air pollution. As of Tuesday, the capital had dealt with 705 environmental pollution cases.

　　A national research center on the causes and control of air pollution will do more research to identify the causes of the smog and make its findings public, the ministry said.

　　The pollution is expected to ease on Wednesday night as colder air moves in, the ministry said.