Atmospheric Environment 40 (2006) 6718–6729 Chemical apportionment of shortwave direct aerosol radiative forcing at the Gosan super-site, Korea during ACE-Asia Jiyoung Kim a,b , Soon-Chang Yoon a,Ã , Sang-Woo Kim a , Fred Brechtel c , Anne Jefferson d , Ellsworth G. Dutton d , Keith N. Bower e , Steven Cliff f , James J. Schauer g a School of Earth and Environmental Sciences, Seoul National University, Seoul 151-747, South Korea b Meteorological Research Institute, Korea Meteorological Administration, Seoul 156-720, South Korea c Brechtel Manufacturing Inc., Hayward, CA, USA d Climate Monitoring and Diagnostics Laboratory, National Oceanic and Atmospheric Administration, 325 Broadway, Boulder, CO 80305, USA e University of Manchester, Institute of Science and Technology, Manchester M60 1QD, UK f University of California at Davis, Davis, CA, USA g University of Wisconsin-Madison, 660 North Park Street, Madison, WI 53706, USA Received 19 December 2005; received in revised form 7 June 2006; accepted 7 June 2006 Abstract Shortwave direct aerosol radiative forcing (DARF) at the surface as well as aerosol optical depth (AOD) were estimated and chemically apportioned on the basis of ground-based aerosol and radiation measurements at the Gosan super-site in Korea during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) in April 2001. An aerosol optical model and a radiative transfer model (RTM) were employed to calculate the aerosol extinction coefficient and radiative flux at the surface, respectively. The calculated scattering and absorption coefficients for D p o10 mm aerosols agreed well with measured scattering and absorption coefficients with root mean square errors (RMSEs) of 23.6 and 3.0 Mm 1 , respectively. The modeled direct and diffuse irradiances at the surface were also in good agreement with the measured direct and diffuse irradiances. In this study we found that the 17-day mean aerosol radiative forcing of 38.3 W m 2 at the surface is attributable to mineral dust (45.7%), water-soluble components (sum of sulfate, nitrate, ammonium, and water-soluble organic carbon (WSOC)) (26.8%), and elemental carbon (EC) (26.4%). However, sea salt does not play a major role. For the cases of Asian dust and smoke episodic events on 26 April 2001, a diurnal averaged forcing of 36.2 W m 2 was contributed by mineral dust (18.8 W m 2 ), EC (6.7 W m 2 ), and water-soluble components (10.7 W m 2 ). The results of this study suggest that water-soluble and EC components as well as a mineral dust component are responsible for a large portion of the aerosol radiative forcing at the surface in the continental outflow region of East Asia. r 2006 Published by Elsevier Ltd. Keywords: Surface aerosol radiative forcing; Extinction; Closure study; Chemical apportionment; Aerosol; ACE-Asia ARTICLE IN PRESS www.elsevier.com/locate/atmosenv 1352-2310/$ - see front matter r 2006 Published by Elsevier Ltd. doi:10.1016/j.atmosenv.2006.06.007 Ã Corresponding author. Tel.: +82 2 880 6717; fax: +82 2 883 4972. E-mail address: yoon@snu.ac.kr (S.-C. Yoon).