Abstract: Aerosol optical depth (AOD) as a kind of MODIS aerosol product,has a high correlation with PM_2.5 (aerosol particulate with the diameter of less than 2.5 μm) concentration,and it has been widely applied in the quantitative simulation of PM_2.5 concentration. However,it is still difficult to accurately estimate the PM_2.5 concentration because of the temporal and spatial differences of AOD.The pretreatment of the vertical humidity correction for MODIS aerosol products can eliminate the influence of uncertainties of the atmosphere to a certain extent,and thus to improve the precision and robustness of the quantitative estimation.Therefore,this paper aimed to bring the vertical humidity correction into the preprocessing of MODIS aerosol product AOD data to analyze the correlation between MODIS AOD products and PM_2.5 concentration in Urumqi,Xinjiang,a typical arid city in northwestern China.The daily MODIS AOD data and PM_2.5 concentration data in the corresponding period from 7 ground monitoring stations (covering different altitudes and functional areas) were selected as the data source.The results showed a good correlation which was further improved after the pretreating correction.The R² (determinant coefficients) of the optimal model was ranged from 0.27 to 0.69 with the higher values (0.55 ≤ R² ≤ 0.69) achieved in spring and autumn,which indicated a better model accuracy while the R² in summer was low (0.27 ≤ R² ≤ 0.41) reflecting a relatively poor performance of the model.The result also demonstrated that the MODIS AOD data could not only be used to quantitatively estimate surface PM_2.5 concentration in the areas of dense vegetation,but also be used in the areas of low vegetation coverage,such as the arid regions in northwestern China.The study provides the reference for the deep utilization of AOD and the estimation of PM_2.5 concentration by means of remote sensing method (MODIS aerosol product AOD),which has important significance in air pollution spatial diffusion process,remote sensing monitoring,and the forecasting of urban atmospheric pollutants in the arid and semi-arid region,especially.

Key words: aerosol optical depth (AOD), PM_2.5, correlation analysis, Urumqi City