Estimation of aerosol effects on surface irradiance based on measurements and radiative transfer model simulations in northern China

Using 15 months' worth of ground- based broadband and spectral radiation data at Xianghe, a suburban site in northern China, aerosol effects on surface irradiance are explored in this study. Collocated aerosol optical depth (AOD) and surface irradiance measurements made under cloudless sky conditions are first binned according to solar zenith angle. Empirical equations are then developed to describe the relationships between AOD and surface shortwave radiation (SWR) and photosynthetically active radiation ( PAR). The equations are finally used to derive quantitative estimates of aerosol effects on surface SWR and PAR. The annual mean aerosol direct radiative forcing (ADRF) values for SWR and PAR derived from measurements are -32.8 and -16.6 W m - 2, respectively, which are in good agreement with those derived from radiative transfer model simulations. Variations in aerosol concentration not only change the amount of global solar radiation reaching the Earth's surface but also alter the relative proportions of diffuse and direct solar radiation. The annual mean changes in direct and diffuse SWR induced by aerosols are -89.6 and 51.0 W m - 2, respectively, and the annual mean changes in direct and diffuse PAR induced by aerosols are - 51.0 and 29.6 W m - 2, respectively. The effects of regional haze in China on climate and crop production should be further studied.