City-level variations in aerosol optical properties and aerosol type identification derived from long-term MODIS/Aqua observations in the Sichuan Basin, China

Abstract

In recent decades, the Sichuan Basin (SCB) has suffered from severe aerosol pollution. Based on the long-term (2003–2018) aerosol optical properties dataset derived from the Moderate Resolution Imaging Spectroradiometer (MODIS), this study investigated the spatial distribution and interannual variation of aerosol optical depth (AOD) and fine-mode fraction (FMF) as well as the aerosol type at city-level in the SCB. The spatial distribution of AOD exhibited a decreasing trend from the centre of SCB to surrounding areas with high AOD approximately 1.0. The high FMF value was approximately 0.9 in surrounding southern areas. The frequency of occurrence of AOD < 0.2 was approximately 30%–40%. AOD in SCB exhibited a negative trend of approximately −0.03/year and FMF showed a significant positive trend of approximately 0.01–0.02/year. The proportion of continental background aerosols was higher in surrounding areas of SCB. The BB/UI (biomass burning/urban-industrial) aerosols in the central urban area increased significantly to approximately 50%. Mix aerosols were mainly distributed in the north, accounting for approximately 35%–45%. A large proportion of dust aerosols (30%–35%) was noted in the east SCB. The results of this study are of great scientific significance for the analysis of aerosol optical extinction at city level in the SCB of China.