Study on black carbon and sulphate aerosols concentrations in and around Bangladesh and its impact on atmospheric variables

Abstract

Atmospheric aerosols have significant local, regional and global impacts. They have the potential to significantly influence the Earth’s climate as they scatter or absorb sunlight. In this study, for the area of Bangladesh and its surroundings, Monitoring Atmospheric Composition & Climate (MACC) reanalysis data with grid resolution of 0.75° X 0.75° collected from European Centre for Medium-Range Weather Forecasts (ECMWF) is used for analyzing annual, seasonal and monthly variations of black carbon (BC) and sulphate aerosols for 10 years from 2003 to 2012. The average values for aerosol optical depth of sulphate and BC aerosols are found 0.152 and 0.016, respectively, which contributes 36.55% and 3.96% of total aerosol in the atmosphere. The yearly variation of sulphate shows increasing tendency with coefficient of determinant (R2) of 0.63 whereas BC remains nearly constant with R2=0.03. Within ten years sulphate aerosol increases 22.22% which is alarming. During pre-monsoon a large amount of aerosol optical depth of sulphate (0.179) is dominated whereas BC shows highest value of 0.022 during winter which is very low compared to sulphate. The monthly distribution of sulphate (black carbon) is periodic in nature with a maximum value of 0.212 (0.025) in May (March) and minimum value of 0.115 (0.007) in November (July). The average wind velocity, temperature, relative humidity and precipitation at 1000, 850, 700, 500 and 300 hPa, respectively are correlated with the concentration of sulphate and BC aerosols. For sulphate, good correlation coefficient (r) are found with wind velocity at 1000 hPa (r=0.69), temperature at 850 hPa (r=0.66), relative humidity at 700 hPa (r=0.58) and precipitation at 1000 hPa (r=0.46), respectively. On the other hand, BC aerosol is positively correlated with wind velocity (r=0.92) and but it shows negative correlation with temperature (r=-0.94) at 700, 500 and 300 hPa, relative humidity at 1000 hPa (r=-0.90) and precipitation at 1000 hPa (r=-0.88). It indicates that after transportation by wind BC aerosol scatters radiation, which results cooling effect in the environment, whereas, sulphate at lower level warms the environment by absorbing radiation. The higher value of relative humidity and associated precipitation washout both BC and sulphate aerosols which causes the decrease in the concentration of aerosols in monsoon season. The environment in the west side of the study area is more affected by the sulphate and BC aerosols than that in the east side because aerosols are transported from the western side of the study area.