Global Wet-Reduced Nitrogen Deposition Derived From Combining Satellite Measurements With Output From a Chemistry Transport Model

Wet-reduced nitrogen (NH4+) is the main component of atmospheric nitrogen (N) deposition. Due to the poor coverage of ground-based measurements, it is still challenging to characterize the global wet-reduced NH4+ deposition. Here we utilize NH3 measurements from satellite retrievals (Infrared Atmospheric Sounding Interferometer) to estimate global wet NH4+ deposition at 0.1 degrees grids for nine years (2008-2016). We achieve this by developing a novel approach by calculating the feedback ratio between wet NH4+ concentration in precipitation and atmospheric NH3 columns using a global chemistry transport model (GEOS-Chem). Satellite-based wet NH4+ concentration and deposition is relatively highly correlated with the ground-based measurements (r = 0.88 and bias = 12% for wet deposition). The largest increase in the satellite-derived wet NH4+ deposition occurs in southern China (>0.5 kg N ha(-1) yr(-1)), followed by northeastern India, North America, and Western Europe. The proposed method is simple, fast, and effective in estimating wet NH4+ deposition using the satellite observations without depending on the ground-based measurements for constructing the models. It is particularly helpful in estimating wet NH4+ deposition over regions with few monitoring sites. Our unique satellite-derived wet NH4+ deposition can be applied for evaluating its impacts on ecosystems in the future.