Declining dry deposition of NO2 and SO2 with diverse spatiotemporal patterns in China from 2013 to 2018

The nitrogen and sulfur deposition results in damages on ecosystems, while the lack of direct observation on dry deposition limits our understanding of the total deposition. This study aimed to improve the methodology and estimates of NO2 and SO2 dry deposition in China and to explore the efficacy of China's recent emission control measures on dry deposition at the national and regional scales. We combined the random forest algorithm and the GEOS-Chem chemical transport model to predict the dry deposition fluxes of NO2 and SO2 and their interannual variabilities during 2013-2018 in mainland China. The annual NO2 dry deposition ranged between 2.1 and 3.1 kg N ha(-1) yr(-1), with an annual reduction rate of 0.21 kg N ha(-1) yr(-1) over this period. The areas with large deposition were located in the east, while the biggest reduction existed in the relatively clean Tibet Plateau region. The annual SO2 dry deposition ranged between 7.5 and 18.4 kg S ha(-1) yr(-1), with the annual reduction rate at 2.4 kg S ha(-1) yr(-1). Both the magnitude and relative reduction in the north were generally larger than the south. Regarding the four typical economically developed regions, the NO2 deposition declined slower than the national average, while SO 2 generally declined faster than or equivalently to the national average, except for Pearl River Delta. The reduced emissions attributed to the national action on air pollution control were identified as an important reason for the declining deposition. However, the increased traffic and industrial capacity in the east weakened its benefit on NO2.

Automated summary

This study utilized a combination of data models and algorithms to predict the dry deposition of NO2 and SO2 in mainland China from 2013 to 2018, finding a reduction in both gases during this period. The eastern regions exhibited higher levels of dry deposition, while the Tibet Plateau showed the greatest reduction.