Inferring aerosol types over the Indo-Gangetic Basin from ground based sunphotometer measurements

A discrimination of aerosol types over the Indo-Gangetic Basin (IGB) region during pre-monsoon period was made using multi-year ground based sun/sky radiometer measured aerosol products associated with the size of aerosols and radiation absorptivity. High dust enriched aerosols (i.e. polluted dust, PD) were found to contribute more over the central IGB station at Kanpur (KNP, 62%) as compared to the eastern IGB station at Gandhi College (GC, 31%) whereas vice-versa was observed for polluted continental (PC) aerosols, which contain high anthropogenic and less dust aerosols. Contributions of carbonaceous particles having high absorbing (mostly black carbon, MBC) and low absorbing (mostly organic carbon, MOC) aerosols were found to be 11% and 10%, respectively at GC, which was ~ 46% and 62% higher than the observed contributions at KNP; however, very less contribution of non-absorbing (NA) aerosols was observed only at GC (2%). Variability in aerosol types together with single scattering albedo (SSA) at both the stations were also studied during the forenoon (FN) and afternoon (AN) hour, which suggests their strong association with emission sources. Results were well substantiated with the air mass back-trajectories and the fire products. Spectral information of SSA for each aerosol type discriminates the dominance of natural dust (SSA increases with increasing wavelength) with anthropogenic aerosols (SSA decreases with increasing wavelength) at both the locations. The estimated absorption Ångström exponent (AAE) values suggest relative dominance of absorbing type aerosols over the central part of IGB (due to dominant dust absorption) as compared to the eastern part during pre-monsoon period.

► Five major categories of aerosols were identified over the IGB during pre-monsoon.
► Variability in aerosol types together with SSA was studied on diurnal basis.
► AAE has been established for each aerosol type over the IGB region.
► Dominant absorbing aerosols were observed at the central IGB region.
► Less absorbing aerosols were observed at the eastern IGB region.