China uses PM 2.5 in weather alert system

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　　The announcement comes as thick haze² chokes many cities.

　　The National Meteorological Center (NMC) has introduced a three-tier color-coded weather warning system to alert the public to the severity of smog. The system uses yellow to imply moderately smoggy weather, orange for severe conditions and red for extremely severe levels of smog.

　　The system not only measures the density³ of PM 2.5, a major pollutant that triggers smog, but also takes into account visibility and relative humidity to better reflect air quality conditions, according to the center.

　　The smog that has blanketed many Chinese cities in recent days has affected⁴ a total area of 1.3 million square kilometers, according to the Ministry⁵ of Environmental Protection.

　　The municipalities of Beijing and Tianjin, together with the provinces of Hebei, Shandong and Henan, will remain the hardest-hit regions on Tuesday evening through Wednesday daytime.

　　However, rain and snow that is expected to fall on Wednesday night will help disperse⁶ the smog in central and eastern regions, the NMC said.

　　Earlier this month, several consecutive⁷ days of smoggy weather choked Beijing and other cities in north and east China, as readings for PM 2.5 far exceeded safe levels.

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