title: Spatial boundary of urban 'acid islands' in southern China.
abstract: Elevated emissions of sulfur dioxide, nitrogen oxides and ammonia in China have resulted in high levels of sulfur and nitrogen deposition, being contributors to soil acidification, especially in and near large cities. However, knowledge gaps still exist in the way that large cities shape spatial patterns of acid deposition. Here, we assessed the patterns of pH, sulfate, nitrate and ammonium in bulk precipitation and throughfall in southern China's forests by synthesizing data from published literature. Concentrations and fluxes of sulfate, nitrate and ammonium in bulk precipitation and throughfall exhibited a power-law increase with a closer distance to the nearest large cities, and accordingly pH showed a logarithmic decline. Our findings indicate the occurrence of urban 'acid islands' with a critical radius of approximately 70 km in southern China, receiving potential acid loads of more than 2 keq ha(-1) yr(-1). These urban acid islands covered an area of 0.70 million km(2), accounting for nearly 30% of the land area in southern China. Despite a significant capacity to neutralize acids in precipitation, our analysis highlights a substantial contribution of ammonium to potential acid load. Our results suggest a joint control on emissions of multiple acid precursors from urban areas in southern China.
authors.affiliation: State Key Laboratory of Earth Surface Processes and Resource Ecology, and College of Resources Science &Technology, Beijing Normal University, Beijing, 100875, China.
authors.forename: E
authors.initials: E
authors.lastname: Du
authors.affiliation: 1] Environmental Systems Analysis Group, Wageningen University, PO Box 47, 6700 AA Wageningen, the Netherlands [2] Alterra, Wageningen University and Research Center, PO Box 47, 6700 AA Wageningen, the Netherlands.
authors.forename: W
authors.initials: W
authors.lastname: de Vries
authors.affiliation: College of Resources and Environmental Sciences, China Agricultural University, Beijing, 100193, China.
authors.forename: X
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Ecology, and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing, 100871, China.
authors.forename: J
authors.initials: J
authors.lastname: Fang
authors.affiliation: Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22904, USA.
authors.forename: J N
authors.initials: JN
authors.lastname: Galloway
authors.affiliation: State Key Laboratory of Earth Surface Processes and Resource Ecology, and College of Resources Science &Technology, Beijing Normal University, Beijing, 100875, China.
authors.forename: Y
authors.initials: Y
authors.lastname: Jiang
mesh_terms: D000143:Acids / Q000032:analysis*; D000397:Air Pollution / Q000032:analysis / Q000706:statistics & numerical data*; D002681:China; D002947:Cities / Q000706:statistics & numerical data*; D004781:Environmental Exposure / Q000032:analysis / Q000706:statistics & numerical data*; D014877:Water Pollution, Chemical / Q000032:analysis / Q000706:statistics & numerical data*
chemical_list: D000143:Acids