Atmospheric aerosol optical depth and its variability over an urban location in Eastern India

Abstract

Eastern India is characterized by high aerosol loading of primarily anthropogenic origin due to both local emissions and long-range transport and hence outflow of air mass from the Indo-Gangetic Plains. Using a year-long measurement of atmospheric aerosol optical properties over Bhubaneswar, one of the fastest growing tier-two cities in the Eastern India, we show that the aerosol optical depth (AOD) varied between 0.39 and 0.96 with high loading during February and low during July. The Angstrom exponent (AE) was found to be mostly higher than unity indicating large dominance of fine mode particles with a larger AE. Further analysis using spectral curvature of AOD and satellite-based estimates indicates that more than 80% of the time, fine mode aerosols dominate the region. It is observed that there is a large diurnal variability in AOD (AE) of the order of 15% (5%) indicating a large change in loading (spectral characteristics) over a short period of within a day. The aerosols types inferred from spectral curvature method match reasonably well with those from MERRA-2 chemical reanalysis. Further, it is found that satellite-derived AOD’s are low biased with respect to ground measurements and are unable to capture seasonality consistently. These findings show that additional research is required to assess the causes for such inconsistency especially during the monsoon period.