1. National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki 305-0053, Japan, Environment Preservation Center, Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501, Japan, and Sumitomo Heavy Industries Ltd., 5-9-11 Kitashinagawa, Shinagawaku, Tokyo 141-8686, Japan