BEIJING, March 26 -- An official with the Ministry of Environmental Protection said on Wednesday that the smog shrouding Beijing and surrounding areas will be dispersed by cool air blowing in after Friday.

Air quality in Beijing has dropped sharply since Sunday. On Monday, the air quality index in the capital hit 271, reaching the band classified as heavy pollution along with other four cities in neighboring Hebei Province.

By 7 p.m. on Wednesday, the density readings of PM2.5 -- airborne particles measuring less than 2.5 microns in diameter -- surpassed 300 in urban districts, according to the Beijing Municipal Environmental Monitoring Center.

The official with the ministry said the weather on Thursday will not help diffuse pollutants and that part of the area surrounding Beijing will continue to suffer severe smog.

However, as cold air arrives on weekend, most of Beijing and the neighboring area will have favorable weather to diffuse air pollutants, the official said.