The selection of PM2.5 monitoring sites is catching the Chinese people's attention.
China's provincial capital cities and municipalities such as Beijing and Tianjin as well as the Yangtze River Delta and Pearl River Delta regions have successively started monitoring PM2.5 – particulate matter 2.5 micrometers or less in diameter.
However, more than half of the monitoring sites in Guangzhou, Nanjing, and some other cities are located in schools and parks, raising public concerns that monitoring data from these locations may be unable to reflect the real pollution situation.
Nanjing-based environmental experts explained that experimental monitoring results have showed that PM2.5 density does not vary much from place to place. PM2.5 can drift in the air for a long time and a long distance, as its diameter is only about 1/20 the thickness of a human hair. The Guangdong Provincial Department of Environmental Protection said that PM2.5 density is either high in all areas or low in all areas.
Such responses are unlikely to ease public concerns. After all, the country previously only conducted small-scale pilot PM2.5 monitoring projects, which could not generate standard or accurate results, and should not be used as the only scientific basis for selecting monitoring sites.
Furthermore, what do the experts mean by PM2.5 can drift "a long distance?" Is it a few kilometers, tens of kilometers, or several hundred kilometers? Even if PM2.5 really can drift a long distance in the air, the public can still feel the difference in the air quality of the city proper and suburbs, and of busy roads and green parks.
Before experts come up with convincing PM2.5 monitoring data, we can first take a look at the distribution of PM10, or respirable particulate matter 10 micrometers or less in diameter.
Take Beijing which has long been plagued by haze as an example. According to a daily air quality report released by the Beijing Municipal Bureau of Environmental Protection on April 26, monitoring sites with "excellent" air quality are all located in outer suburban areas with good ecological environment, including the Miyun Reservoir, Ming Tombs in Changping, and Beijing Botanical Garden in Haidian district.