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November 7, 2012

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Stricter norms to cut good air-quality days

THE annual number of days with excellent or good air quality in Shanghai may drop by 20-30 percentage points from the current level after a stricter air quality criterion is put into effect late next week.

Under a new national standard, Shanghai will rate local air quality based on six indicators, instead of three, starting November 16, officials from the Shanghai Environment Monitoring Center said yesterday.

At present, excellent or good air quality is reported for about 330 days, or 90 percent of a year. The number will be cut to between 220 and 255 days, according to the new standard.

The center's website will issue daily and hourly readings of air quality index (AQI), namely, a composite index of PM10, sulfur dioxide, carbon dioxide, PM2.5, ozone and carbon monoxide levels.

Air quality will be indicated by six levels from excellent to severely polluted, with each level assigned a different color, starting from green as the excellent to maroon as the severely polluted.

Currently, Shanghai rates its air quality according to three readings of the air pollution index (API): PM10, sulfur dioxide and carbon dioxide.

Also, the daily index of air quality under AQI will be evaluated for 24 hours from the previous midnight, while the API system is from the previous noon.

Lin Chenyuan, a forecaster at the center, said the center will issue timely warnings on air pollution through its website, microblog and public media under the new system.

"Of the three new indicators, PM2.5 is drawing the biggest public concern as it can affect air quality and visibility and raise doubts in people's minds about the air quality forecast," Lin said.

PM2.5 is a measure of airborne pollutants smaller than 2.5 microns in diameter, which are the main cause of urban smog and haze and are harmful to human health.

Shanghai's air quality today is expected to be on the verge of light pollution again due to sandstorms from the north and light winds. The PM2.5 density was more than 80 micrograms per cubic meter for the entire day yesterday.

By 5pm, the hourly reading of PM2.5 was 109.8 micrograms per cubic meter, and the reading for the past 24 hours was 96.4 micrograms per cubic meter. The nation's standard within 24 hours is 75 micrograms per cubic meter.


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