Analysis of Chemical Compositions of Cloud Water and Rain Water During the Plum Rains Period in Shanghai

During the plum rains period of June-July, 1986, the pH values of cloud water and surface rain water were measured in Shanghai, and their chemical compositions were also analysed. These results indicate that: (1) The acidification of rain water is caused by sulphates in Shanghai; (2) The rain acidity is related to its chemical compositions. In cloud water and rain water with higher pH values (pH≥6.00), Ca2+ content is the highest, and with pH＜5.00, SO content is the highest; (3) The acidification of altostratus (As) precipitation is mainly due to washout process below the cloud, and the rain acidity of nimbostratus (Ns) is mainly due to rainout process in the cloud. Further, the acidification of cloud water in Ns may be affected not only by the local air pollutants transported upward but also by the distant air pollutants through the advection transportation