Optical and radiative properties of aerosols over Desalpar, a remote site in western India: Source identification, modification processes and aerosol type discrimination.

Aerosol optical properties are analyzed for the first time over Desalpar (23.74°N, 70.69°E, 30m above mean sea level) a remote site in western India during October 2014 to August 2015. Spectral aerosol optical depth (AOD) measurements were performed using the CIMEL CE-318 automatic Sun/sky radiometer. The annual-averaged AOD500 and Ångström exponent (α440-870) values are found to be 0.43±0.26 and 0.69±0.39, respectively. On the seasonal basis, high AOD500 of 0.45±0.30 and 0.61±0.34 along with low α440-870 of 0.41±0.27 and 0.41±0.35 during spring (March-May) and summer (June-August), respectively, suggest the dominance of coarse-mode aerosols, while significant contribution from anthropogenic sources is observed in autumn (AOD500=0.47±0.26, α440-870=1.02±0.27). The volume size distribution and the spectral single-scattering albedo also confirm the presence of coarse-mode aerosols during March-August. An overall dominance of a mixed type of aerosols (~56%) mostly from October to February is found via the AOD500 vs α440-870 relationship, while marine aerosols contribute to ~18%. Spectral dependence of α and its second derivative (α') are also used for studying the aerosol modification processes. The average direct aerosol radiative forcing (DARF) computed via the SBDART model is estimated to range from -27.08Wm-2 to -10.74Wm-2 at the top of the atmosphere, from -52.21Wm-2 to -21.71Wm-2 at the surface and from 10.97Wm-2 to 26.54Wm-2 within the atmosphere. This atmospheric forcing translates into heating rates of 0.31-0.75Kday-1. The aerosol properties and DARF are also examined for different trajectory clusters in order to identify the sources and to assess the influence of long-range transported aerosols over Desalpar.