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Meteorological and aerosol data were measured at the atmospheric boundary layer observation station in Tianjin,China,and were analyzed to study the effects of aerosol mass,composition,and size distributions on visibilityand short-term radiation flux.The results show that fine particles played important roles in controllingvisibility in Tianjin.The major contributors to light extinction coefficients included sulfate (28.7%),particulate organic matter(27.6%),elemental carbon(19.2%),and nitrate(6.1%).In addition to the measurementof aerosol composition,the size distribution of aerosol number concentrations were also measured and classifiedbetween haze days and non-haze days during spring.The extinction characteristics of ambient aerosol in hazedays and non-haze days were calculated using Mie theory model.The average extinction coefficient and scatteringcoefficient of atmospheric aerosols were 0.253 km-1and 0.213 km-1 in non-haze days,while 0.767 km-1and 0.665 km-1in haze days.A radiation transmission model LOWTRAN7 is also applied in this study.The model calculated radiantflux densities in haze days and non-haze days,which showed a fairly agreement with the observation results,showing that the heavy aerosol loadings in Tianjin had significantly impact on atmospheric visibility andradiation fluxes.