| Filter samples of PM10 were taken twice a week at ten CAWNet stations of the Chinese Meteorological Administration from Jan. to Dec. 2006, and at three additional sites from Oct. to Dec. 2007. The sites were in regions of rapid economic growth and urbanization, including urban, rural, and regional backgrounds.Nine inorganic ions were measured by ion chromatography: F-,Cl-,NO3-,SO42-,Na+,NH4+,K+,Mg2+,and Ca2+. These data were used to study spatial and temporal variations of sulfate, nitrate and ammonium in different regions of China. The major conclusions were as follows:1. Ranges of aerosol concentrations for the three types of sitesThe yearly average mass concentration of sulfate was 25~48μg/m3 at urban sites, 23~27 ug/m3 at rural sites, and 12μg/m3 at a regional background site. Nitrate averaged 13~29μg/m3, 7.4~15μg/m3 and 5.6μg/m3 at urban, rural, and regional sites, respectively, and ammonium was 9.3~18μg/m3, 6.7~8.0μg/m3 and 2.9 ug/m3. PM10 was 137~295μg/m3, 84~141μg/m3, and 67μg/m3.Relative to EU countries, the U.S., Japan, and Korea, China's sulfate concentration is significantly high, although it is comparable to Vietnam. The contrast is less significant for nitrate, which at some urban and rural sites in China is comparable to Taiwan and the western U.S.2. Spatial distribution of major water-soluble speciesSulfate was generally highest at urban sites. Concentrations were highest in Zhengzhou, Xi'an, Chengdu, and Gucheng, and lower in the Yangtze River region. Urban sulfate was lowest in Pearl River and Beijing. The concentration in Beijing in fall 2007 was lower than in fall 2002. Sulfate at rural sites in the Huazhong Region was higher than at urban sites in Shanghai, Beijing, and Panyu. Nitrate was also highest at urban sites. Regional concentrations were highest in the Yangtze River region, the Huabei Plain and the Guanzhong Plain, and lower in Sichuan and the Pearl River region.Sulfate was more regional than nitrate.3. Chemical composition of PM10Sulfate, nitrate and ammonium made up more than 30% (30%~51%)of PM10 at all the sites, and the total soluble ions more than 37% (37%~60%). Sulfate was the most abundant ion (12%~32%), followed by nitrate (7%~15%),ammonium (5%~9%), and Ca2+(2%~5%).The mass fraction of sulfate was larger at rural sites than at urban sites in the same region, and was larger in the south than in the north. In the Huazhong region, sulfate made up 30% of the PM10, and secondary inorganic aerosol more than 43%.4. Seasonal and monthly variations of aerosolSeasonal variations of aerosols concentrations in the north and the south show two typical patterns, with the variations being greater in the north. In the north, sulfate, nitrate and ammonium peak in winter, while sulfate and ammonium are lowest in spring, and nitrate lowest in summer. In the south (Panyu, Changde and Jinsha), sulfate and ammonium peak in the fall, and nitrate and ammonium are lowest in summer, as in the north.The chemical composition of PM10 also varies seasonally. The mass fraction of sulfate is largest in summer at almost all sites. At the northern sites, water-soluble ions make up the smallest fraction of PM10 in spring.The monthly variations of aerosol depend on the site, too. Some sites have a peak in Oct., which may create an overall fall peak for these sites.The seasonal and monthly variations of aerosol are not only associated with emissions, but also with meteorological patterns and sources of air masses.
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