Analysis and Monitoring of the Spatio-temporal Aerosol Patterns over Bangladesh

Nowadays climate change is the burning issue and atmospheric aerosols are vital parameter of the global climate system. So, atmospheric aerosols are one of the hot topics for present scientific research. Most remote sensing methods retrieve aerosol optical depth (AOD) to assess the aerosols and their various effects on environmental and climate system. However, there is lack of studies dealing with monitoring of aerosol patterns over Bangladesh. In this research, we have analyzed the spatial and temporal variations in aerosol load over Bangladesh, using MODerate resolution Imaging Spectroradiometer (MODIS) Level 3 remote sensing data. A Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model was used to generate a backward trajectory in order to identify the origins of air masses, with the aim of understanding these spatial and temporal variabilities in aerosol concentrations. During the last decade, AODs have increased across Bangladesh and revealed a higher AOD concentration in western part but a much cleaner environment in eastern part. An assessment of monthly mean variations in AOD has exhibited maximum AODs in June and minimum AODs in October. Looking over seasonal variations during the last decade over Bangladesh showed maximum AOD values during the summer, while minimum AOD values showed during the post monsoon also an evidence of a decreasing AOD trend showed during the monsoon can be owing to an increase in monsoonal rainfall in Bangladesh, while all other seasons showed increasing trends. Northwestern part of Bangladesh has showed at the top of AOD concentration in winter season during the year 2010. Dense fog activities in northern part of Bangladesh may be the causes of this high AOD distribution. We also documented, the regional AOD variations over seven different divisions of Bangladesh, for which Dhaka and Sylhet divisions showed decreasing trends where all others showed increasing trends. Annual mean AODs have highest levels in Rajshahi and Khulna and lowest level in Sylhet. Back trajectory analysis indicates that Bangladesh is mainly affected by the pollutions and desert dust of India combining with sea salt particles blown from the Arabian Sea. The sources of air masses were arriving at lower altitudes (500m, 1500m) mainly in western India and Indian subcontinent but higher altitude (2500m) air masses were loading especially in winter season from far western regions, such as Europe and various sub-Sahara region of Africa. However, an exceptional result was observed in post monsoon of 2010 that different flow patterns of air masses were observed that the air masses were arriving in Sylhet from southeast in the direction, the sources of air masses were in coastal region of Thailand and the boarder region of Myanmar and China. The air masses were arriving at several divisions in different seasons from different distances and directions owing to the variations of wind velocities and wind directions. These studies become important and useful to proceed about climate change in Bangladesh. However, more and more studies are required to understand about atmospheric aerosol properties and their climate impacts.