Trend and Interannual Variations of Reactive Nitrogen Deposition in China During 2008-2017 and the Roles of Anthropogenic Emissions and Meteorological Conditions

Abundant emissions have made China as one of the hotpots of atmospheric reactive nitrogen (Nr) deposition over the world. Here we conducted multi-year simulation and explored the trend and interannual variations (IAVs) of China's Nr deposition for different forms (wet and dry) and species (oxidized and reduced nitrogen, OXN and RDN) during 2008-2017. Sensitivity analysis scenarios were applied to evaluate the roles of anthropogenic emissions and meteorological conditions on the changing deposition. The annual mean Nr deposition was simulated at 15.7 +/- 0.9 kg N ha(-1) yr(-1) for China. Attributed mainly to the changing OXN, the trend in Nr deposition over the 10-year period showed an inverted "V" pattern, reflecting the benefit of nation actions on NOX emissions controls. The standard deviation ellipse analysis suggested a clear interannual shift of spatial distribution of Nr deposition to the southwest during 2013-2017. Based on the mean absolute deviation (MAD) and absolute percent departure from the mean obtained in different simulation scenarios, the IAVs of Nr deposition were found to be driven mainly by the changing meteorological conditions, and the correlation coefficient between MADs of Nr deposition and precipitation reached 0.47. Relative to meteorological factor, the changing emissions could explain 61%-83% of 10-year trend of Nr deposition for the concerned regions, thus were identified as the main driver of the trend. The changing meteorological conditions played a more important role on shaping the IAVs of Nr deposition, with the relative contributions estimated at 60% for the concerned regions. Due to abundant anthropogenic emissions, China has been a hotspot of deposition of atmospheric reactive nitrogen (Nr), which exerts multiple ecological and environmental damages. During the past decade, China has been implementing aggressive actions of air pollution controls, leading to large changes in Nr emissions and thereby deposition. The evolution of Nr deposition as well as its major influencing factors is of great concern for both scientific community and policy makers. We conducted numeric simulation and geographic analysis, to explore the spatiotemporal change of Nr deposition and to separate the contributions of anthropogenic (emissions) and natural (meteorological conditions) to the change for 2008-2017. We found a clear growth of Nr deposition till 2012 followed by a decline afterward for the whole country, and unequal changes in different regions resulted in a shift to southwest for the spatial distribution of Nr deposition since 2012. The changing emissions were identified as the major contributor to the trend of Nr deposition, while meteorological conditions played a more important role on its interannual variation. The outcomes improve the understanding of driving forces of the changing Nr deposition in China, and reveal the effectiveness of national pollution controls on it.