Chemical composition of precipitation in a forest area of Chongqing, Southwest China

Abstract

Experiments were carried.out in Chongging-a city seriously damaged by acid precipitation in southwest China — to explore chemical compositions of open bulk precipitation, throughfall and stemflow in a Masson pine (Pinus massoniana) forest. The results showed that annual mean pH values of and annual ion depositions in the three types of rain water were 4.47 and 50.6 g m⁻², 3.82 and 69.7 g m⁻², and 2.92 and 0.215 g m⁻² respectively. pH values demonstrated an obvious seasonal variation; they were lower in winter than in the rest of the year. Ca²⁺ and NH ^sup+_inf4 together made up more than 80% of the total cation, while SO ^sup2−_in4 alone contributed over 90% to the total anion. This high level of SO ^sup2−_in4 in rain water in Chongqing, which outran those found in other cities in China, was closely related to the combustion of locally produced coal that contains 3 to 5% sulphur. Thus, acid precipitation in Chongqing is of a typical sulphuric-acid type.