Aerosol optical properties and direct radiative forcing in Tianjin
Based on the analysis of solar radiometer observation data in Tianjin in 2021,we have obtained the variation characteristics of AOD(Aerosol Optical Depth),AE(Angstrom Exponent),FMF(Fine Mode Fraction),volume size distribution,complex refractive index,and direct radiative forcing.The research results indicated that affected by the sand-dust weather in spring and the hygroscopic growth and secondary conversion of aerosols in summer,the AOD values in spring and summer were 0.64 and 0.61 respectively,significantly higher than those in autumn and winter.The seasonal variation of AE in Tianjin ranged from 0.99 to 1.29.The volume spectrum distribution of aerosol particles exhibited a bimodal distribution characteristic.The peaks of the coarse and fine mode particle size spectrum reached of the highest in spring and summer respectively,with values of 0.07μm3/μm2 and 0.05μm3/μm2 respectively.When AOD was greater than 0.4,the peak concentration of fine mode particles increaseed significantly and approaches the peak concentration of coarse mode particles.In summer,SSA reached 0.93,with the real part of the complex refractive index being 1.43 and the imaginary part being 0.07.In winter,the AAOD value was 0.10,and AAE was 1.15.Aerosol particles with strong extinction capability were concentrated in the range of AAE from 1.0 to 1.2 and SSA from 0.90 to 0.95.The main aerosol types in Tianjin were mixed absorbing particles,accounting for 40％,followed by fine-mode absorbing particles at 33％.The scattering and extinction capability of aerosols had a direct relationship with the increased in relative humidity and FMF.When the relative humidity was higher than 60％,aerosols were mostly types of Ⅲ to Ⅵ.When the aerosol was type of Ⅶ,FMF was less than 0.4;when the aerosol was type of V,FMF ranges from 0.4 to 1.0;and when the aerosol was types of Ⅰ to Ⅲ,FMF was 0.8 to 1.0.The mean values of aerosol direct radiative forcing at the ground,top of the atmosphere,and in the atmosphere were-71.9W/m2,-14.9W/m2,and 57.1W/m2 respectively.The direct radiative forcing of aerosols was closely related to AOD and SSA.An increased in AOD by one unit resulted in changed in the direct radiative forcing of aerosols at the top of the atmosphere,ground,and in the atmosphereby-28.4W/m2,-99.4W/m2,and 70.9W/m2,respectively.The correlation coefficients with SSA were-0.85,0.89,and-0.93respectively.As SSA increaseed,the absolute values of the direct radiative forcing efficiency at the ground and in the atmosphere decrease,while the direct radiative forcing efficiency at the top of the atmosphere gradually shifted from a heating effect to a cooling effect.Through the analysis of a haze-dust weather process in Tianjin from March 9th to 16th,2021,it was found that during the haze episode,fine particle pollution mainly occurred in the form of urban-industrial aerosol types.The hygroscopic growth of aerosol particles led to the increased in the size of fine particles as pollutants accumulated,enhancing the scattering ability of aerosols and their cooling effect on the near-surface air,thus inhibiting the development of the boundary layer and causing a positive feedback mechanism between pollutants and the boundary layer.
万方数据
维普
