Shanghai plagued by heavy pollution

City's air quality index reaches 254, the highest reading in two months

Shanghai residents breathed the most polluted air they had seen in two months on Wednesday as weak cold air from the north brought pollutants to the Yangtze River Delta.

But clean air is expected on Thursday thanks to another round of cold air, forecasters said.

Seasonal factors played an important role as winter is the high pollution season, and straw burning in nearby provinces also contributed to the pollution, experts said.

Shanghai's air quality index, a new air quality reporting system that monitors sulfur dioxide, nitrogen dioxide, carbon monoxide, ozone, PM10 and PM2.5, reached 254 by 7 pm on Wednesday.

The figure, which indicated the air had reached the level of heavy pollution, was the highest seen since the index was introduced two months ago, according to the Shanghai Environmental Monitoring Center.

Shanghai's hourly density of PM2.5, air particles smaller than 2.5 microns, also reached 250 micrograms per cubic meter by 10 am, while the reading was only 60 micrograms per cubic meter early Tuesday morning.

The heavy pollution in the eastern metropolis followed thick air pollution in Beijing over the weekend. Beijing's density of PM2.5 broke the record since the municipality began publishing the data in early 2012 as its figure went higher than 900 micrograms per cubic meter in several districts of the city on Saturday.

Lin Chenyan, a forecaster with Shanghai Environmental Monitoring Center, said the cold front brought in airborne pollutants from the north.

"The cold snap is like a broom sweeping down all the way to Shanghai, and it brings the dust here," said Lin, adding that atmospheric motion sometimes causes trouble such as that.

Before arriving in Shanghai, the pollutants had left some of Shanghai's neighboring provinces shrouded in smog and fog.