The importance of calcium deposition in assessing impacts of acid deposition in China

The extensive use of coal as an energy carrier in China has led to high dep osition of sulfur in a large part of the country. In the southern part of C hina large areas receive acid deposition, while in the northern part of the country the acidity of the emissions is neutralized by alkaline dust from the desert areas. In this paper we demonstrate the importance of knowing th e sources and deposition patterns of base cations when assessing the effect s of changes in sulfur emissions. Regional-scale data of both sulfur and ca lcium deposition from modeling and monitoring are combined in order to demo nstrate how the acidity of deposition in China has changed historically and may change in the future. The importance of base cation deposition is also demonstrated using the dynamic acidification model MAGIC with input data f rom an intensive monitoring site outside Guiyang. It is not known what frac tion of the deposited base cations is of natural origin and anthropogenic o rigin, respectively. The relative source strength varies greatly between re gions. Future effects of emission changes are highly dependent on the relat ive reduction in sulfur and base cation emissions.