Aerosol particles can directly alter the radiation balance by scattering and absorbing incident solar radiation, thus decreasing the amount of light reaching the surface and increasing the fraction of diffuse radiation—the so-called ‘aerosol direct radiative effect’. Using the Moderate Resolution Imaging Spectroradiometer aerosol products, the aerosol direct radiative effects under all-sky conditions in Beijing and Shanghai in 2007 were explored in this study. The total shortwave radiation was calculated using the Fu-Liou radiative transfer model, with the influence of clouds taken into account through sunshine-duration data, and the diffuse radiation was calculated with radiation decomposition models. Good correlation between measured and calculated total radiation was obtained at both cities, with an R greater than 0.9, and thus this calculation method was adopted to derive aerosol direct radiative effects. The presence of aerosols caused the mean total and diffuse solar radiation reaching the surface to change by ?19.9% and +27.4% in Beijing, respectively, and by ?18.4% and +6.5% in Shanghai. It was also found that, despite the strong negative correlation between aerosol optical depth and total radiation change, the diffuse radiation changes were determined predominantly by clouds. The effects of such changes induced by aerosols on plant productivity should be further studied.
气溶胶能够吸收和散射太阳辐射，使到达地面的太阳总辐射减小，同时增加其中散射辐射所占比例。这个效应被称为气溶胶的直接辐射效应。本研究基于MODIS数据，借助Fu-Liou大气辐射传输模型来对2007年北京和上海全天候条件下的气溶胶直接辐射效应进行估算，其中云天下的辐射效应计算利用了日照时数的数据以及辐射分解模型。结果显示气溶胶使得北京的地表总辐射平均减少了19.9%，辐射辐射平均增加了27.4%；使得上海的地表总辐射平均减少了18.4%，辐射辐射平均增加了6.5%。同时还发现总辐射的变化与气溶胶光学厚度有着很强的相关性，而散射辐射的变化则主要受到云的影响。