Spatial and temporal variation of aerosol optical depths over six major cities in Bangladesh

The Aerosol Optical Depth (AOD) is a crucial parameter for assessing aerosol content and determining the level of air pollution. In this study, we represent almost seven years' aerosol optical behavioral patterns of six major cities in Bangladesh with emphasis on trends, seasonal variations, sources characterization, comparison between ground (AERONET) and satellite (MODIS Terra and Aqua) measurements, and relation with particulate matter (PM). High AOD values (>0.70) were obtained in most of the western parts of the country in all seasons. Decreasing patterns were observed from northwest to southeast. Average values of AOD for Dhaka, Chattagram, Rajshahi, Khulna, Barishal, and Sylhet were 0.71 +/- 0.08, 0.50 +/- 0.08, 0.78 +/- 0.06, 0.72 +/- 0.14, 0.64 +/- 0.08, 0.60 +/- 0.07 (Terra), and 0.59 +/- 0.07, 0.48 +/- 0.05, 0.69 +/- 0.08, 0.64 +/- 0.12, 0.56 +/- 0.05, 0.56 +/- 0.07 (Aqua), respectively. AERONET AODs at 870, 500, and 340 nm, and Angstrom Exponent (AE(440-870)) values for Dhaka city were 0.40, 0.78, 1.06, and 1.18, respectively. Mean Absolute Error (MAE), Root Mean Square Error (RMSE), and Correlation coefficient (r) values were 0.23, 0.30, 0.64 (Terra) and 0.12, 0.29, 0.76 (Aqua), respectively. Both PM2.5 and PM10 were well correlated with all AODs but weakly correlated with AE. AODs, AE, and PM were negatively associated with meteorological variables such as rainfall, relative humidity, wind speed, and temperature. Anthropogenic and biomass burning aerosols were dominated in all four seasons, but dust and mixed type aerosols were only dominated in pre-monsoon and monsoon seasons. This research would help researchers further know the nature of atmospheric aerosols and how they affect seasonal patterns.