The wet deposition fluxes of acidic substances were observed on the mountainside (1300 m a.s.l.) of Mt. Fuji from July 2005 to November 2006 by a solar-powered automatic rainwater collector, which was developed with emphasis on its being small-size, lightweight, and inexpensive for use in wet deposition monitoring network in mountainous area. The collector is divided into two parts, namely rainwater collection and solar battery system. The former is composed of a capacitance-type rain sensor, an originally designed automatic switching cover, a polycarbonate filter holder (80 mm in diameter), which is equipped with a 47 mm diameter and 1.2 μm pore size membrane filter, a polyethylene bottle, and a polypropylene tube connecting the holder and the bottle. The latter is composed of a 20 watt solar panel, a solar charge controller, and a 12 V lead acid battery. A comparison of the deposition fluxes, estimated by the automatic rainwater collector with those by a filtering-type rainwater collector, indicated that they were free of the influence of dry deposition without a loss of rainfall in the automatic rainwater collector. Rainfall amounts estimated by the automatic rainwater collector corresponded to those observed by a commercially available rain gauge except for winter. Annual wet deposition fluxes of H +, NO 3 -, and SO 4 2- in the mountainside on Mt. Fuji were 58.5, 40.4, and 78.8 meq/m 2/y, respectively.
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