BEIJING, Oct. 10 (Xinhua) -- The Beijing-Tianjin-Hebei region and its nearby areas have been shrouded in smog since Wednesday due to seasonal changes and poor atmospheric circulation, although air quality is expected to improve from Sunday, according to the Ministry of Ecology and Environment on Saturday.

Shijiazhuang in Hebei Province, in particular, saw moderate air pollution, with the concentration of hazardous PM2.5 airborne particles standing at 147 micrograms per cubic meter as of 3 p.m. Saturday, the ministry said.

Air conditions in the region will gradually improve from Sunday afternoon, thanks to the northwest cold-air effect, according to the ministry.

Strong temperature inversion, high humidity and weak southeast winds are conducive to the accumulation of pollutants, including PM2.5 particles, said Chai Fahe, chief scientist of the Chinese Research Academy of Environmental Sciences.

From Oct. 12 to 14, large parts of the region will see good air quality due to improving atmospheric circulation, the ministry said.