Aerosol optical properties are analyzed for the first time over Desalpar (23.74 degrees N, 70.69 degrees E, 30 m 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 AOD(500) and angstrom ngstrom exponent (alpha(440-870)) values are found to be 0.43 +/- 0.26 and 0.69 +/- 0.39, respectively. On the seasonal basis, high AOD(500) of 0.45 +/- 0.30 and 0.61 +/- 0.34 along with low alpha(440-870) 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 (AOD(500)= 0.47 +/- 0.26, alpha(440-870)= 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 (similar to 56%) mostly from October to February is found via the AOD(500) vs alpha(440-870) relationship, while marine aerosols contribute to similar to 18%. Spectral dependence of a and its second derivative (alpha') 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 -27.08 W m(-2) to -10.74 W m(-2) at the top of the atmosphere, from -52.21Wm(-2) to -21.71Wm(-2) at the surface and from 10.97W m(-2) to 26.54 Wm(-2) within the atmosphere. This atmospheric forcing translates into heating rates of 0.31 - 0.75 K day(-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. (C) 2016 Elsevier B.V. All rights reserved.

The present study addresses the role of black carbon (BC) in aerosol radiative forcing (ARF) over western India, where the Thar Desert produces large amount of dust aerosols during pre-monsoon season (Mar-May) and its mixing with BC makes the investigation a real challenge. Measurements of aerosol physical and optical parameters were carried out at three stations, Ahmedabad (urban area), Udaipur (semi-arid region) and Mt. Abu (a hill-top representing background conditions), to investigate the regional variation of ARF during April 2007. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) measurements show presence of dust layer in the altitude region from 1 to 5 km over western India throughout the month leading to uniform distribution of dust. Ahmedabad has slightly higher AOD(500) (0.31) due to production of anthropogenic aerosols with BC concentration of 1.8 mu g.m(-3) at surface, followed by Udaipur (AOD(500) = 0.30 and BC = 0.9 mu g.m(-3)) and Mt. Abu (0.28 and 0.7 mu g.m(-3), respectively). The longwave ARF is found to be similar over all three stations whereas the shortwave ARF depends on type of location. The shortwave ARF at the top of atmosphere (TOA), surface, and within the atmosphere are found to be 1.7, -46 and 47.7W m(-2), respectively, at Ahmedabad, -1.5, -35 and 33.5W m(-2) at Udaipur and -1.5, -31 and 29.5W m(-2) at Mt. Abu. On the other hand, the heating rates in the lower atmosphere (up to 5 km) are 1.3, 1.0 and 0.4 K/day over Ahmedabad, Udaipur and Mt. Abu, respectively. Sensitivity analysis shows that a 40% enhancement of BC could increase the heating rate by up to 50% over western India. Higher aerosol-induced heating in the atmosphere during premonsoon may have a large impact on the regional climate dynamics and hydrological processes. (C) 2011 Elsevier B.V. All rights reserved.