6Balasubramanian R.,Victor T.,and Chun N.,Chemica and statistical analysis of precipitation on Singapore[J].Water Air and Soil Pollution,2001,130:45-456.
7Lee Yin-nan,Shen Ji and Paul J.Klotz.Chemical composition of precipitation at Long Island,NY.[J].Water Air and Soil Pollution,2002,30:143-152.
