Quantifying the wet deposition of reactive nitrogen over China: Synthesis of observations and models.

Accurate estimation on reaction nitrogen (N) deposition is highly demanded for assessing the impacts on the environment and human beings. This study investigated the wet deposition of inorganic nitrogen (IN) in mainland China by measurements from over 500 sites from five observational networks/databases and ensemble results of eleven chemical transport models (CTMs). Each data source has its focus and limitations and together formed a comprehensive view over China. But the inconsistency among different sources may hinder the appropriate usage of data. Model evaluation results demonstrated the models' deficiency in simulating the wet NO deposition over Southeast China (40 % underestimation) and showed an overall underestimation of wet NH deposition over the hotspot regions (5-60 % underestimation). A synthesis of this study and twelve reference studies was conducted to quantify the national amount of wet IN deposition. The estimations by CTMs ranged 2.4-3.9 Tg(N) yr for wet NO deposition and 4-6.7 Tg(N) yr for wet NH deposition, after adjusting the results with 10-19 % underestimations in wet NO deposition and 1-40 % underestimations in wet NH deposition. The estimations by ground observations ranged 7.1-9 Tg(N) yr for wet NO deposition and 8-13.1 Tg(N) yr for wet NH deposition, which were 20-275 % higher than the estimation by CTMs, but the results were strongly influenced by the abundances and representative of measurements. Studies using statistical techniques to interpolate site observations predicted 3-5.5 Tg(N) yr for wet NO deposition and 3.9-7.2 Tg(N) yr for wet NH deposition. This approach benefited from high accuracy and good robustness of the statistical models, but the uncertainty in the interpolation methods could be a potential drawback.