Chemical composition of precipitation in Beijing area, northern China

Variations of anions (SO42-, NO3-, NO2-, Cl- and F-), cations (K+, Na+, Ca2+, Mg2+ and NH4+) and pH values in precipitation, througfall and stemflow samples collected over a four-year period (1995-1998) in Beijing (two sites Zhongguancun and Mangshan) are presented. The annual volume-weighted range of pH values were 6.57-7.11 in precipitation, 5.46-6.86 in thoughfall and 5.32-6.41 in stemflow. The fominant anion was SO42-, while Ca+ and NH4+ were the main cations in precipitation, throughfall and stemflow. Most of ion concentrations with precipitation, throughfall and stemflow volume showed negative correlation, except for some ones. Significant correlation values were also found between ions (SO42-, NO3-, Cl-, F-, Ca2+, Mg2+ and Na+) in precipitation, throughfall and stemflow indicated the common sources of these ions such as coal combustion, automobile emission and fertilizers application. Compared to precipitation, there was an increased ion concentration in throughfall or in stemflow. Changes of ion concentrations were in Quercus liatungensis Koiz. and Pinus tabulaefornis Carr. throughfall (or stemflow) because of different crown and bark qualities of tree species.