An Investigation of Aerosol Size Distribution Properties at Dibrugarh: North-Eastern India

Columnaraerosol size distributions, retrieved from spectral AOD (aerosol optical depth) esti mates over a northeastern location of India (Dibrugarh) are, ingeneral, bimodal with the occurrence of primary (broad) mode at 0.04 - 0.17 m and the secondary mode at 0.88 - 1.29 m. The physical parameters of size distributions representing the microphysical properties of aerosols show distinct sea sonal variations with the highest value of the effec tiveradii (~ 0.55 m) during pre-mon soon (March to May) season which, along with the highest value of AOD (~ 0.46 ¡__n0.09) during the same season, is attributed to the maxi mum abundance of coarsepa ticles. Examining the re sults in the light of the HYSPLIT back tra jectory analy sis and the peruliar to pogr phy of northeast India allowing advection only from the Indo-Gangetic plains or Bay-of-Ben gal, it appears that the strong presence of the coarse mode aerosols are associated with either mineral dust or marine aerosol components or both