A Study On The Effect Of Black Carbon Aerosol On Surface Ultraviolet Radiation Under Clear Sky Conditions

Ultraviolet radiation（UV）is solar radiation in the wavelength range from 10 to400 nm.Although a relatively small part of solar radiation,UV radiation can have important effects on climate,environment,ecosystems and human health.Factors that affect UV radiation include solar zenith angle,cloud cover,aerosols,ozone,air molecules and surface albedo,among which aerosols attenuate UV radiation by absorption and scattering.Black carbon aerosols are strong absorbers and can have a significant effect on the surface UV radiation.A large number of studies on the influence of black carbon aerosols on surface UV radiation have been carried out at different sites and a series of important progresses have been made.However,due to the limitations of data and model simulations,the trends of black carbon aerosols and UV radiation in typical regions on a global scale and the relationship between them are not still clear,and there is a lack of quantitative assessment of the impact of black carbon aerosols on surface UV radiation in typical regions.Therefore,this thesis analyzes the spatial and temporal distributions and trends of black carbon aerosol column concentrations and terrestrial UV radiation on a global scale from 2001 to 2021and their interrelationships using MERRA-2（Modern-Era Retrospective Analysis for Research and Applications,Version 2）reanalysis data and CERES（Clouds and the Earth’s Radiant Energy System）satellite retrieval data.On this basis,the direct effects of black carbon aerosols on the surface UV radiation were quantified by using the TUV（Troposphere Ultraviolet and Visible Radiation Model）radiative transfer model,and the differences between the effects of black carbon aerosols and total aerosols on the surface UV radiation were compared.The main results and conclusions are as follows:（1）To verify the accuracy of model simulations,MERRA-2 reanalysis data were input into the TUV radiative transfer model for simulations,and the simulation results were compared with the observations of the World Ozone and Ultraviolet Radiation Data Centre（WOUDC）and the CERES satellite retrieval data.The simulation results are in good agreement with the observations,with correlation coefficients greater than0.90 and small root mean square error and mean absolute percentage error.Therefore,the TUV radiative transfer model simulations in the paper have good accuracy.（2）Using MERRA-2 reanalysis data and CERES satellite inversion data,the spatial distribution and trends of global black carbon aerosol column concentrations and surface UV radiation from 2001 to 2021 were analyzed.Four regions with high black carbon aerosol column concentrations（eastern China,Indian Peninsula,central Africa and central South America）and two regions with relatively lower concentrations（western Europe and eastern North America）were further selected for in-depth study.The results show that the net black carbon aerosol column concentration increases by0.11 mg·m^-2 on accumulate from 2001 to 2021 for global mean,and the surface UV radiation is significantly lower in the region with high black carbon aerosol column concentration than in the surrounding areas.The black carbon column concentration decreases significantly in eastern China,increases significantly in the Indian Peninsula and central Africa,and does not change significantly in central South America,eastern North America and western Europe.The surface UV radiation in the region of high black carbon aerosol column concentration has the opposite trend to that of black carbon aerosol.（3）Using the MERRA-2 reanalysis information as input data for the TUV,the spatial and temporal distribution of the effect of black carbon aerosol on surface UV radiation under clear-sky condition was studied by first simulating six typical regions for 2021.As a comparison,the effect of total aerosol on surface UV radiation is also simulated as a comparison of black carbon aerosol.There are obvious spatial and temporal characteristics of the effects of black carbon aerosol on surface UV radiation in eastern China.The high value areas are mainly found in Beijing,Tianjin,Hebei,southern Henan and northern Hunan.The largest total attenuation occurs in August(7.1W·m^-2),which is mainly due to both black carbon aerosol column concentration and UV radiation intensity.（4）In Indian Peninsula,the high value of the total attenuation of black carbon aerosol impact on surface UV radiation is located in the India River and Ganges River Campagna due to the monsoon and emission,and reaches the maximum(10.5 W·m^-2)in February.In central Africa,the high value of total attenuation shifts north-south near the Congo basin due to two rainy seasons and reaches a maximum in August(18.0W·m^-2).In central South America,the high value area of total attenuation is scattered by forest wildfires,with the maximum value in August(15.2 W·m^-2).In the relatively clean western Europe and eastern North America,the maximum total attenuation is 2.5and 5.1 W·m^-2,respectively.（5）From 2001 to 2021,the average results for each typical region show that although the concentration of black carbon aerosol is a low percentage of the total aerosol concentration（7.0%）,its effect on UV radiation is a high percentage of the total aerosol effect on UV radiation（37.2%）.