Study On The Physical Characteristics Of Black Carbon Aerosol In Chin

Black carbon（BC）aerosols remain one of the significant uncertainties in the assessment of aerosol-climate effects due to their complicated physical properties.This thesis employs the MERRA-2 reanalysis data to systematically study the characteristics of BC atmospheric loading,dry and wet depositions and radiative forcing over China from 1981–2020.This hopefully benefits not only for understanding BC physical properties over China,but also for the evaluations of aerosol-climate models and the studies of climate change.（1）The BC average surface mass concentration in China is 1.15μg/m³,while its mean column mass density is observed to be 1.46 mg/m².The BC loading shows distinct spatial distributions with high values over the Beijing-Tianjin-Hebei region and Sichuan basin,and it generally decreases during recent 10 years.Significant seasonal and monthly variations of BC loading are seen,with high values in winter and low levels in summer.The potential source regions of BC over China are local emissions and long-range transport of air pollutions,showing diverse patterns in different seasons.（2）The dry deposition flux of BC exhibits high values over the Beijing-Tianjin-Hebei region and Sichuan basin of China,whereas large BC dry deposition velocity is seen in the Tibet Plateau.The mean dry deposition fluxes of hydrophobic and hydrophilic BC in China are6.83×10^-4 and 5.87×10^-4μg m^-2 s^-1,respectively,whilst their eatimated dry deposition velocities of 6.16×10^-4and 5.15×10^-4m/s are seen.High BC concentration or strong wind speed is beneficial to BC dry deposition.（3）The high wet deposition flux of hydrophilic BC is found in the Sichuan Basin with a mean value reaching 1.00×10^-2μg m^-2 s^-1,whereas its average value over the whole China is only2.38×10^-3μg m^-2 s^-1.The BC concentration and precipitation are two important factors in favor of high BC wet deposition in the Sichuan Basin,among which BC concentration plays a more important role.The wet deposition flux of hydrophilic BC contributes to 80.2%of its total deposition over China.（4）The BC surface,top of atmosphere（TOA）and atmospheric shortwave mean direct radiative forcings（DRFs）over China based on the SBDART model are-11.08,1.12 and 13.21W/m²,respectively.Aerosol surface,TOA and atmospheric shortwave DRFs and surface longwave DRF in China are observed to be-12.53,-5.40,7.05 and 1.03 W/m²,respectively.Aerosol DRFs show distinctive spatial distribution with a high surface longwave DRF reaching～6.5 W/m² over the Taklamakan desert,and it increases with increasing decade.Dust has strong influences on shortwave aerosol direct radiative forcing among column aerosol compositions,and stronger impacts of aerosol scattering than absorption on the TOA radiation budgets are found in China.Our study indicates general underestimations of atmospheric aerosol DRF over China by aerosol-climate models.