Spatial and Temporal Changes of Aerosol Optical Depth in Last Two Decades over Bangladesh

Satellite-derived Aerosol Optical Depth (AOD) plays a crucial role in assessing both climate change and air quality impacts on human health at local to global scales. This study investigates the spatial and temporal variations of aerosol loading over Bangladesh during the last two decades (2002–2021) using AOD products retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor aboard the Terra satellite. Aerosol distribution patterns were analyzed using three MODIS retrieval algorithms: Dark Target (DT), Deep Blue (DB) and their combined dataset (DTB). The results show consistently high AOD values (> 0.60) in western Bangladesh, with elevated aerosol regions gradually expanding towards the northeastern, eastern, and southeastern parts of the country. Seasonal analyses indicate the highest aerosol concentrations during the pre-monsoon season and the lowest during the post-monsoon period. Average AOD values for DT, DB and DTB products during pre-monsoon were 0.71, 0.61 and 0.71, respectively, whereas post-monsoon averages were 0.43, 0.40, and 0.44. Monthly trends show peak AOD in July and a minimum in October. To assess the accuracy of MODIS retrievals, AOD values were validated using ground-based observations from the Aerosol Robotic Network (AERONET) at two stations located at Dhaka University and Bhola sites in Bangladesh. The validation showed that the DB algorithm performed better in urban conditions, whereas DTB provided more reliable estimates in coastal regions. The findings from this study offer valuable insights into the long-term aerosol distribution patterns over Bangladesh and their implications for regional climate and environmental research.