Dry Deposition of Hydrophilic Black Carbon Aerosols in China

Abstract

Atmospheric dry deposition of black carbon (BC) is a significant but poorly understood and inadequately described process in aerosol-climate models. The 40-year detailed dry deposition velocities of hydrophilic BC over China from 1981 to 2020 were systematically studied based on the MERRA-2 reanalysis data, which hopefully will be beneficial for its applications in atmospheric systems for climate and air quality. The average dry deposition flux of hydrophilic BC over China was 0.00059 ± 0.00014 μg m−2 s−1, while its dry deposition velocity was estimated to be 0.00051 ± 0.00004 m s−1. The monthly mean dry deposition fluxes of hydrophilic BC varied nearly 1.5 fold, ranging from the lowest 0.00046 ± 0.00011 μg m−2 s−1 in August to the highest 0.00068 ± 0.00019 μg m−2 s−1 in January. The spring season had the highest mean dry deposition flux of hydrophilic BC, followed by summer and winter, whereas autumn showed relatively weaker dry deposition flux. The mean dry deposition velocities of hydrophilic BC over the Beijing-Tianjin-Hebei region, Yangtze River Delta, Pearl River Delta and Tibet Plateau were estimated to be 0.00042 ± 0.00004, 0.00042 ± 0.00004, 0.00051 ± 0.00006 and 0.00078 ± 0.00005 m s−1, respectively. The monthly and seasonal patterns of dry deposition velocities of hydrophilic BC differed from each other in different regions, and high air temperature or surface wind speed seemed to fortify dry deposition velocities of hydrophilic BC. Our study pointed to high dry deposition flux of hydrophilic BC in the northern China Plain and Sichuan Basin but large dry deposition velocities in the Tibet Plateau region.