The Wet Deposition of Selenium and Future Changes in China

Selenium (Se) is one of the essential dietary elements of human beings, which can improve immunity, prevent from cancer, slow down the aging process and help cure COVID-19. About 29~36 Gg Se are emitted into atmosphere each year and the atmospheric Se returns ecosystem through deposition, especially the wet deposition. Se atmospheric deposition is the major way to supply Se in soils on a global scale. However, an inconsistency between distributions of Se anthropogenic emission and soil Se concentration has been found in China. To explain the inconsistency, the Se emission inventory and Se atmospheric chemistry are implemented in GEOS-Chem to reproduce the distributions of atmospheric concentration and deposition. The model results suggest that the distribution of soil Se concentration is consistent with that of Se deposition in China, with the correlation coefficient *R = 0.7. The distribution of Se wet deposition is similar to precipitation but not to anthropogenic emission in China, which suggests that precipitation is a more controlling factor of Se wet deposition than atmospheric concentration. With China realizing carbon neutral goal around 2060, Se deposition is supposed to decrease strikingly and further reduce Se content in soils. The scenario of carbon neutrality, SSP1-2,6 has been simulated to explore the future distributions of Se concentration and deposition in China. The results show that the natural source will replace anthropogenic source as the main contributor of soil Se. The wet deposition fluxes decline by more than 80% in most areas compared to 2010, leading to a serious situation of Se deficiency across China in the future.