Acid Deposition and Soil Acidification in China: A Multipollutant Perspective

Yu Zhao1, 2*, Lei Duan2, Yu Lei1, 2, Jia Xing2, Chris P. Nielsen1 and Jiming Hao2

To explore the future trends of soil acidification in China, a multipollutant framework is applied combining the possible variations of emission and deposition of sulfur (S), nitrogen (N) and particulate matter (PM). Under ongoing SO2 control regulations for power sector and the assumptions of forthcoming NOX control policies, national emissions of SO2, NOX and NH3 in 2020, the target year of this study, are estimated to be 23.0, 23.4 and 22.0 Mt, i.e., 78%, 124%, and 132% of the levels in 2005, respectively. Emissions of base cations (BC), the important species mitigating acidification, are calculated with detailed technology information by sector in 2005 and projected for 2020 under two scenarios, one a base case and the other with stronger emission control policies. The anthropogenic emissions in 2005 and base and control scenarios in 2020 are estimated to be 5970, 7147 and 3250 kt for Ca2+, and 236, 462, and 308 kt for Mg2+, respectively. Depositions of acidifying species (i.e., S and N) and BCs are simulated with the Community Multiscale Air Quality (CMAQ) model and a multi-layer Eulerian model respectively. From 2005 to 2020, S depositions in north-central and eastern China, the most polluted areas, are estimated to decline by over 20%, while N deposition will rise by at least 10% in all provinces except Tibet even with application of denitrogenation technologies in the power sector. Compared to 2005, BC deposition will increase by 16% in the base scenario 2020, but decrease by 32% in the control scenario. By comparing the simulated S, N, and BC depositions and critical load (CL), the criterion of acidification below which harmful ecological effects do not occur, current and future soil acidification are evaluated in terms of exceedance of CL. In 2005, the area exceeding CL covered 15.6% of mainland China, with a total exceedance of 2.2 Mt S. These values will decrease to 14.1% and 1.8 Mt S, respectively, in the base scenario 2020, implying recovery from soil acidification. In the control scenario, however, the respective estimates are 17.9% and 2.4 Mt S, implying even higher acidification risks than 2005, particularly in south-central and eastern China. In other words, the recovery from soil acidification in China may be delayed substantially by PM control motivated mainly by human health benefits. To better understand the different effects of atmospheric pollutants, a multieffect perspective should be taken combining local, regional and global environmental considerations.

1*Corresponding author phone: 1-617-496-2410; fax: 1-617-384-8016;email:
1School of Engineering and Applied Science, Harvard University, 29 Oxford St., Cambridge, MA 02138
2Department of Environmental Science and Engineering, Tsinghua University, Beijing 100084, China