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BEIJING, Dec. 28  -- Chinese cities of Beijing, Tianjin and those in the surrounding areas are once again shrouded in heavy smog that is expected to last until Tuesday night, the national observatory forecast on Sunday.

The PM2.5 readings in those regions started to climb on Saturday night, prompting Beijing and Hebei Province to issue yellow alerts for the pollution, according to the National Meteorological Center (NMC).

Starting on Tuesday night, a cold front will gradually disperse the pollution, the NMC said.

China has a four-tier color-coded weather warning system, with red representing the most severe weather, followed by orange, yellow and blue.

PM2.5, airborne particles smaller than 2.5 microns in diameter, is a key indicator of air quality. Beijing's average PM2.5 index came in at 89.5 micrograms per cubic meter in 2013.

After experiencing frequent bouts of smog, the Chinese public has become increasingly sensitive to the health hazard.

To address public concerns, the government aims to cut the density of inhalable particulate matter by at least 10 percent in major cities by 2017.