Atmospheric Environment 38 (2004) 4701–4708 Characteristics of water-soluble components of atmospheric aerosols in Yokohama and Mt. Oyama, Japan from 1990 to 2001 Masaki Takeuchi a , Hiroshi Okochi a , Manabu Igawa a, * a Department of Applied Chemistry, Faculty of Engineering, Kanagawa University, 3-27-1, Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan Received 7 November 2003; received in revised form 6 May 2004; accepted 20 May 2004 Abstract We continuously collected aerosol samples of PM 7 from 1990 to 1997 and of PM 10–2 and PM 2 from 1998 to 2001 and measured their water-soluble components of pH, conductivity, major ions, dissolved organic carbon (DOC) and total mass (TM) in an urban site, Yokohama (35  28 0 N, 139  38 0 E) and the mountainside (680masl) of Mt. Oyama (35  28 0 N, 139  46 0 E, 1252m asl), Japan, to contrast the aerosol composition between an urban site and a mountain site. In Yokohama, annual mean TM concentration decreased gradually for over 10 years with the decrease of NH 4 + , Mg 2+ , Cl  , and SO 4 2 concentrations, and TM concentrations were the highest in winter and the lowest in summer. At Mt. Oyama, there was no significant change in the duration, and TM concentrations were the highest from late spring to early summer, although the seasonal variation was smaller. Equivalent concentration ratio of Cl  to Na + at Mt. Oyama was lower than that in Yokohama, because Cl loss which occurred was larger for the aerosol collected at Mt. Oyama remote from the sea rather than Yokohama. The conversion ratio of sulfur to sulfate was calculated and the ratio was not affected strongly by the variation of O x concentration at both sites and was high at Mt. Oyama in summer. NH 4 + , NO 3  , SO 4 2 , and DOC concentrations were higher under weak wind velocity than those under strong wind velocity regardless of the wind direction in both the sites. r 2004 Elsevier Ltd. All rights reserved. Keywords: Dissolved organic carbon; Major ions; Mountain area; Particle size; Urban area 1. Introduction In order to investigate the effect of air pollutants on the natural environment and ecology system, we need to measure not only the wet depositions but also the dry depositions, e.g. gases and aerosols. The dry deposition of aerosols, particularly those containing acidic species such as nitrate and sulfate, causes the acidification of lakes, rivers, and soils. The air pollution of aerosols spreads out over broad regions (Chan et al., 1997; Wakamatsu et al., 1996) because the aerosols remain in the air for several days (Wojcik and Chang, 1997). We have been investigating acid fog at Mt. Oyama in the Tanzawa Mountain on the southwest of the Kanto Plains, where many of the virgin firs are dead. At the mountain, the acid fog events frequently occur and canopies capture the acid fog containing many air pollutants which are carried upward through a moun- tain slope by valley winds (Igawa et al., 1998, Igawa et al., 2002). We have also measured the air pollution at our university in Yokohama for the comparison of that in Mt. Oyama. Yokohama is a big city abutting on the ARTICLE IN PRESS AE International – Asia *Corresponding author. Tel.: +81-45-481-5661x3880; fax: +81-45-491-7915. E-mail address: igawam01@kanagawa-u.ac.jp (M. Igawa). 1352-2310/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2004.05.027