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The POLDER sensitivity to aerosol size is investigated based on PARASOL and AERONET observations made during 2005-2013. In this study, three AERONET sites: Xianghe, Beijing (China) and Banizoumbou (Niger) where aerosols are dominated by the rural emission, urban pollution and desert dust, respectively, are selected, and the data are screened and matched with PARASOL observations. Then, the AOD870 (aerosol optical depth at the central wavelength of 870 nm) within different size ranges is calculated using AERONET data and compared with POLDER AOD. The POLDER sensitivity is determined by looking for the best fit between the calculated AOD and the POLDER AOD. The results show: (1) The POLDER sensitivity is around 0.27 mu m. (2) The AOD contributed by particles with radius less than 0.27 mu m can be retrieved with high quality by using POLDER measurements. (3) Even using POLDER measurements, the retrievals in rural areas are still better than in urban. This study will help us properly understand the POLDER remote-sensing products and use them in climate studies, therefore improve our understanding of the role of human activities in climate change.