Estimating nitrogen and sulfur deposition across China during 2005-2020 based on multiple statistical models

Due to the rapid development of industrialization and substantial economy, China has become one of the global hotspots of nitrogen (N) and sulfur (S) deposition following Europe and the USA. Here, we developed a dataset with full coverage of N and S deposition from 2005 to 2020, with multiple statistical models that combine ground-level observations, chemistry transport simulations, satellite-derived vertical columns, and meteorological and geographic variables. Based on the newly developed random forest method, the multi-year averages of dry deposition of oxidized nitrogen (OXN), reduced nitrogen (RDN) and S in China were estimated at 10.4, 14.4 and 16.7 kg N/S ha⁻¹ yr⁻¹, and the analogous numbers for total deposition were respectively 15.2, 20.2 and 25.9 kg N/S ha⁻¹ yr⁻¹ when wet deposition estimated previously with a a generalized additive model (GAM) was included. The dry to wet deposition ratio (R_dry/wet) of N stabilized in earlier years and then gradually increased especially for RDN, while that of S declined for over ten years and then slightly increased. The RDN to OXN deposition ratio (R_RDN/OXN) was estimated to be larger than 1 for the whole research period and clearly larger than that of the USA and Europe, with a continuous decline from 2005 to 2011 and a more prominent rebound afterwards. Compared with the USA and Europe, a more prominent lagging response of OXN and S deposition to precursor emission abatement was found in China. The OXN dry deposition presented a descending gradient from east to west, while the S dry deposition a descending gradient from north to south. After 2012, the OXN and S deposition in eastern China declined faster than the west, attributable to stricter emission controls. Positive correlation was found between regional deposition and emissions, while smaller deposition to emission ratios (D/E) existed in developed eastern China with more intensive human activities.