Chemical characteristics of precipitation at three Chinese regional background stations from 2006 to 2007

Studies on the chemical composition of wet precipitation were carried out from September 2005 to September 2007 at three Chinese regional background stations. All samples were analyzed for pH and major ions (F−, Cl−, NO−3, SO42−, K+, Na+, Ca2+, Mg2+ and NH4+). Of the three stations, the lowest pH value was observed at Lin'an. The highest ion concentrations (SO42−, NO3− and NH4+) occurred at Shangdianzi. By referring to former studies and observations of reactive gases at the three stations, pH and chemical composition trends from 1985 to 2007 were analyzed. Compared to values from 1985 to 1997, the pH values in the precipitation of all three stations were significantly lower and [NO3−] was higher. [SO42−] in the precipitation also increased at Shangdianzi and Longfengshan. Due to the neutralization of alkaline aerosols in northern China, precipitation at Shangdianzi and Longfengshan was not as severely acidified as at Lin'an. However, the neutralizing effects of the aerosols have decreased in recent years. Significant correlations between ions were found at each of the three stations. Principal component analysis was also performed to find possible sources of the major ionic species. Acid rain research in China has traditionally focused on urban sites, however the present study of background stations revealed significant effects of long-range transported air pollutants on rural areas in China.