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May 11, 2011

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The air we breathe

SOME question the city's air pollution standard because it doesn't include data on harmful fine particles, reports Jia Feishang.

Although Shanghai's air quality has turned good after a sandstorm brought the worst pollution on record to the city last week, some city residents began to question the standard of the Chinese mainland's Air Pollution Index (API), claiming it's lower than those in other countries or regions.

Under the mainland's system, an API score between 51 and 100 is rated good, which means there are no health implications. In Hong Kong, the same score range means a high pollution level that may lead to chronic effects if one is persistently exposed to such levels.

Chen Wenhui, a meteorology enthusiast who also does environmental research, tells Shanghai Daily that he thought both the city and country don't properly monitor air quality and that "our standard is obviously lower than those in other countries."

"If we adopted the US standard, the number of good air quality days might drop by 80 percent compared with the days calculated under our current system," Chen says.

But Fu Qingyan, a senior engineer with the Shanghai Environment Monitoring Center, which monitors air quality in the city, dismisses this claim and says the mainland's standard is in accordance with the one used in the United States. But based on the chart below, there are big differences in standards used by the two countries.

In addition, Chen also questions why the mainland's system does not include statistics on PM2.5, or particles less than 2.5 micrometers in diameter. The mainland monitors PM10, or suspended particulates with a diameter less than 10 micrometers.

Fine particles are believed to pose greater health risks than suspended particulates as their size, approximately 1/30th the average width of a human hair, can lodge deep into the lungs and result in death in extreme circumstances. Suspended particulates, though they can be inhaled into the lungs, do not cause deaths.

"I think we should include the monitoring of PM2.5 as soon as possible, because they have hazardous effects on the human body," Chen says.

Fu says the city also monitors PM2.5, but they do not release the data to the public because it is not required.

The mainland's API level, fixed about 10 years ago, is based on the level of five atmospheric pollutants - sulfur dioxide, nitrogen dioxide, suspended particulates, carbon monoxide and ozone.

The suspended particulates are heavier and fall to the ground faster, thus making the air seem cleaner. Only when a large amount of pollutants enter the air will PM10 statistics reach the "slightly polluted" level.

According to Chen, even if the city said the air quality was good, it could be polluted since they are not monitoring fine particles.

Chen also says he could understand that the city is developing quickly so there will be more construction sites causing pollution, but "we should know the real situation."


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