Aerosol radiative forcing over a high-altitude station Merak, in the trans-Himalayan region during advection of anthropogenic events from the Indo-Gangetic Plain Shantikumar S. Ningombam a, * , S.P. Bagare a , A.K. Srivastava b , B.J. Sohn c , H.-J. Song c , E. Larson d a Indian Institute of Astrophysics, 2nd Block Koramangala, Bangalore, Karnataka 560034, India b Indian Institute of Tropical Meteorology, (New Delhi Branch) Prof. Ram Nath Vij Marg,New Delhi 110060, India c School of Earth and Environmental Sciences, Seoul National University, Seoul, South Korea d Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO 80309, USA highlights  AOD increases by 117% during advection event (AE) than the background condition.  Fine-mode of absorbing aerosols are dominant during the AE.  During AE atmospheric forcing increases about 78% than the background condition.  Consequently, atmospheric heating rate increases about four times during the AE. article info Article history: Received 17 June 2014 Received in revised form 24 August 2014 Accepted 25 August 2014 Available online 27 August 2014 Keywords: Anthropogenic aerosols Absorbing aerosols Fine-mode Atmospheric forcing Heating rate abstract Advection of anthropogenic aerosols from the Indo-Gangetic Plain (IGP) and dust aerosols from distant deserts towards a high-altitude station Merak, in the trans-Himalayan region are reported during June eJuly 2011. In order to differentiate the advection event, aerosol optical properties were examined during aged background conditions at the site. During the aged background conditions, aerosol optical depth (AOD at 500 nm) and Angstrom exponent (a) at the station were ~0.06 and 1.36, respectively which were increased to 0.13 and 1.62, respectively during the advection event. Further, a strong signature of fine- mode aerosol volume size distribution, dominated by absorbing aerosols, was observed during the advection event. The average atmospheric forcing during the aged background condition was found to be 0.57 Wm 2 (with corresponding heating rate of 0.05 Kday 1 ) and these results were enhanced to 2.58 Wm 2 (with corresponding heating rate of 0.22 Kday 1 ) during the advection event. The present study reveals that during the advection event, heating rate in the atmosphere was increased by about four times than the aged background condition. Such atmospheric warming in the region may influence the melting of the Himalayan glaciers and consequently it may effect the local atmospheric circulation. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Aerosols generated at any given location are often transported over long distances and produce scattering and absorption of solar irradiance (Hoppel et al., 1990). Such scattering and absorption of solar irradiance produces cooling or heating on the earth surface and warming or cooling in the atmosphere. The effect of aerosols on climate is expressed in the term, aerosol radiative forcing (ARF), which can be defined as the effect of aerosols on solar radiative fluxes at the top of the atmosphere, at the surface and within the atmosphere. According to IPCC (2001), the global average radiative forcing by aerosols is 1.2 Wm 2 , whereas it is about þ2.6 Wm 2 for greenhouse gases. However, the accurate estimation of ARF is a matter of major concern (IPCC, 2007, 2013) due to uncertainties introduced by the heterogeneity of aerosols from various sources and sinks at the measuring site. Further, aerosol measurement at the high-altitude stations, particularly in the foot-hills of Hima- layas, are crucial for various climatic implications, and more * Corresponding author. E-mail address: shanti@iiap.res.in (S.S. Ningombam). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv http://dx.doi.org/10.1016/j.atmosenv.2014.08.061 1352-2310/© 2014 Elsevier Ltd. All rights reserved. Atmospheric Environment 98 (2014) 253e259