5-Year study of rainwater chemistry in a coastal mega-city in South China

Abstract

South China is one of the major regions suffering from acid rain in the world, especially for its urban environments. However, long-term and comprehensive studies on rainwater chemistry in this region have been scarce in the literature. In order to characterize the current acid rain status in South China, a total of 208 rainfall events were collected and measured systematically at an urban site in Shenzhen, a mega-city on the southeast coast of China, from 2005 to 2009. The volume-weighted mean (VWM) pH was observed to be 4.56 during the five years, with an acid rain frequency of 84.6%. SO 4 2− was the most abundant ionic species, followed by Ca 2+, NH 4 +, H +, NO 3 −, Cl −, Na +, Mg 2+, K + and F − in sequence. Formic, acetic and oxalic acids together contributed 2.32% to the total organic carbon (TOC) content and 2.86% to the total free acidity. SO 4 2−, NO 3 −, Ca 2+, NH 4 + and TOC presented a seasonal trend of being lower in summer and higher in winter, while the other species did not show clear seasonal patterns. Based on the dataset, the sources of the species in rainwater in Shenzhen were explored using different statistical techniques, which indicated strong impact of anthropogenic pollution on the rainwater chemistry in this area.