Aerosols Direct and Indirect Impact Over Varanasi region.

A comprehensive study of aerosol scattering and absorption characteristics were investigated at an ancient Indian city Varanasi in the eastern Indo-Gangetic Basin (IGB) during the period from January 2019 to December 2021 using different in-situ measurements. The scattering coefficient (σsp at 525 nm) varied between 0.58 and 1198.97 Mm−1 (mean~72.92±134.47 Mm−1) during the entire study period, which was about ten times higher than the absorption coefficient (σabs at 525 nm ~41.94 ±40.70 Mm−1). Seasonally, σsp and σabs were substantially higher during the winter/post-monsoon periods. The magnitude of SSA (at 525 nm) varied between 0 and 0.84 (mean: 0.52 ± 0.30). Further, the magnitude of scattering Ångström exponent (SAE) and back-scattering Ångström exponent (BAE) showed a wide range from -1.08 to -0.58 and -0.16 to 5.04 respectively which suggests large variability in aerosol sizes and emission sources. Relatively higher aerosol backscatter fraction (b at 525 nm) during the monsoon (0.33 ± 0.02) suggests more inhomogeneous scattering, associated with the coarser dust particles. However, lower value of b during winter (0.17 ± 0.01) is associated with more isotropic scattering due to dominance of smaller size particles. This is further confirmed with the estimated asymmetry parameter (AP at 525 nm), which exhibits opposite trend with b. The aerosol optical parameters derived from this study were incorporated into a radiative transfer model to estimate aerosol radiative forcing. The resulting radiative forcing and atmospheric heating rates will be presented in the final results.