Atmospheric Environment 41 (2007) 4638–4652 Optical and chemical properties of marine boundary-layer aerosol around Japan determined from shipboard measurements in 2002 Masataka Shiobara a,Ã , Keiichiro Hara a,1 , Masanori Yabuki b,2 , Hiroshi Kobayashi c a National Institute of Polar Research, Kaga 1-9-10, Itabashi-ku, Tokyo 173-8515, Japan b Center for Environmental Remote Sensing, Chiba University, Chiba, Japan c Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Kofu, Japan Received 6 August 2006; received in revised form 20 March 2007; accepted 21 March 2007 Abstract Shipboard measurements of the optical and chemical properties of marine boundary-layer aerosol were made around Japan over the period from 28 August to 25 September 2002. Measurements were conducted aboard the Research Vessel (R/V) Shirase along cruise tracks beginning from Yokosuka, and proceeding on to Hakodate, Sakata, Sasebo, Naha, Kure, and Yokkaichi. This paper describes the results of optical measurements using an Optical Particle Counter (OPC), an Integrating Nephelometer (IN), and a Particle Soot/Absorption Photometer (PSAP), as well as chemical analyses of water-soluble aerosol particles collected by impactor and filter systems. Coulter Multisizer measurements were used for water-insoluble aerosol particles. The complex refractive index (CRI), scattering and absorption coefficients, and size distribution of aerosols were estimated from combined measurements made using OPC, IN, and PSAP. Contrasting aerosol characteristics were observed during different stages of the cruise. Discussion on these differences focuses mainly on two legs: Leg-1 from Yokosuka to Hakodate and Leg-4 from Sasebo to Naha. Backward trajectory analyses indicate that the air sampled during Leg-1 originated from the Pacific Ocean, whereas the air sampled during Leg-4 originated from the Chinese Continent via the Korean Peninsula. For the first half of Leg-1, the number concentration was low and larger particles were relatively predominant. The real and imaginary parts of the CRI were estimated to be 1.38–1.40 and close to zero, respectively. This estimation is consistent with the results of chemical analyses, which show that the sea salt is rich in aerosols sourced from remote ocean areas. In contrast, small particles were predominant during Leg-4, and the real and imaginary parts of the CRI were estimated to be 1.52–1.59 and approximately 0.002, respectively. These findings are also consistent with chemical analyses that reveal a mixture of mineral dust and sulfate aerosol likely transported from China and Korea. The Coulter Multisizer measurements conducted during Leg-4 reveal abundant water-insoluble particles with a mode radius of 1.35 mm. r 2007 Elsevier Ltd. All rights reserved. Keywords: Aerosol; Optical and chemical properties; Japan; Shipboard measurement ARTICLE IN PRESS www.elsevier.com/locate/atmosenv 1352-2310/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2007.03.048 Ã Corresponding author. Tel.: +81 3 3962 4740; fax: +81 3 3962 4914. E-mail address: shio@nipr.ac.jp (M. Shiobara). 1 Present address: Faculty of Science, Fukuoka University, Fukuoka, Japan. 2 Present address: National Institute of Polar Research, Tokyo, Japan.