Role of black carbon in aerosol properties and radiative forcing over western India during premonsoon period S.K. Das a, b, ⁎, A. Jayaraman a a National Atmospheric Research Laboratory, Gadanki, Tirupati-517 502, India b Presently at Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan article info abstract Article history: Received 21 February 2011 Received in revised form 22 July 2011 Accepted 11 August 2011 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 through- out 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 μg.m -3 at surface, followed by Udaipur (AOD 500 = 0.30 and BC = 0.9 μg.m -3 ) and Mt. Abu (0.28 and 0.7 μg.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 at- mosphere (TOA), surface, and within the atmosphere are found to be 1.7, -46 and 47.7 W m -2 , respectively, at Ahmedabad, -1.5, -35 and 33.5 W m -2 at Udaipur and -1.5, -31 and 29.5 W m -2 at Mt. Abu. On the other hand, the heating rates in the lower atmo- sphere (up to 5 km) are 1.3, 1.0 and 0.4 K/day over Ahmedabad, Udaipur and Mt. Abu, respec- tively. 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. © 2011 Elsevier B.V. All rights reserved. Keywords: Aerosol Black carbon Dust Radiative forcing Western India 1. Introduction In recent years, global climate has received considerable at- tention due to increase in the percentage contribution of an- thropogenic aerosols on the Earth's radiation budget (e.g. Haywood and Ramaswamy, 1998; Kim and Ramanathan, 2008). One of the major anthropogenic components in the at- mospheric aerosols is black carbon (BC) or soot, released from incomplete combustion of carbon-based fuels (Andreae and Gelencsér, 2006). BC has a major contribution toward global warming as it is the second most important component after CO 2 and it has higher direct radiative forcing than that of meth- ane due to its light absorbing capability (Jacobson, 2001). Due to the short life-time of BC in the atmosphere, its concentration is highest in the regions of its production, e.g., industrialized areas and regions influenced by biomass burning, where a strong aerosol radiative forcing (ARF) occurs (e.g. Kiehl and Briegleb, 1993; Ramanathan et al., 2001; Kaskaoutis et al., 2011). Observations during Indian Ocean Experiment (INDOEX) showed that absorbing aerosols (like BC) increased the atmo- spheric solar absorption, reducing the amount of incoming solar radiation which could slow down the hydrological cycle Atmospheric Research 102 (2011) 320–334 ⁎ Corresponding author at: National Atmospheric Research Laboratory, Gadanki, Tirupati-517 502, India. E-mail address: sanatkrdas@gmail.com (S.K. Das). 0169-8095/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.atmosres.2011.08.003 Contents lists available at SciVerse ScienceDirect Atmospheric Research journal homepage: www.elsevier.com/locate/atmos