An investigation of aerosol size distribution properties at dibrugarh: North-eastern India

Abstract

Columnar aerosol size distributions, retrieved from spectral AOD (aerosol optical depth) estimates over a northeastern location of India (Dibrugarh) are, in general, bimodal with the occurrence of primary (broad) mode at 0.04-0.17 μm and the secondary mode at 0.88-1.29 μm. The physical parameters of size distributions representing the microphysical properties of aerosols show distinct seasonal variations with the highest value of the effective radii (∼0.55 μm) during pre-monsoon (March to May) season which, along with the highest value of AOD (∼ 0.46 ± 0.09) during the same season, is attributed to the maximum abundance of coarse particles. Examining the results in the light of the HYSPLIT back trajectory analysis and the peculiar topography of northeast India allowing advection only from the Indo-Gangetic plains or Bay-of-Bengal, it appears that the strong presence of the coarse mode aerosols are associated with either mineral dust or marine aerosol components or both.