Chemical compositions of precipitation and scavenging of particles in Beijing

Totally 23 precipitation samples were collected in Beijing from May to November in 2003. In order to investigate the chemical composition of precipitation samples, pH, conductivity, concentrations of water-soluble ions and organic acids were analyzed. The average pH of precipitations is 6.18, belonging to the neutral range; the average conductivity is 52.23 mu S/cm, which indicates that precipitations in Beijing are obviously polluted; SO42-, NO3- are the most abundant anions with the average concentrations of 521 and 174 mu eq (.) L-1, respectively; the average SO42-/NO3- equivalent ratio is 3.1, which decreases by about 15% compared with the result of 1994; NH4+ and Ca2+ are the most abundant cations with the average concentrations of 376 and 397 mu eq (.) L-1, respectively; formic acid, acetic acid and oxalic acid are the main organic acids with the average concentrations of 4.62, 4.60 and 1.17 mu eq (.) L-1, respectively, accounting for 2% of the overall anions. Obvious differences between concentrations before and after precipitation are also observed by SJAC (Steam Jet Aerosol Collector), which shows the removal of particles from the atmosphere by precipitation.