Distribution of atmospheric SF₆ around urban area in Japan

－Impact for groundwater dating using SF₆－

Abstract

To understand distribution of the atmospheric SF₆ mixing ratio is vital for groundwater dating using SF₆. Monitoring of the atmospheric SF₆ ratios were conducted at three major metropolitan areas and one rural area, to clarify spatial distribution of the atmospheric SF₆ in and around urban area in Japan. All the measured values exceeded Northern Hemisphere clean air levels. The average excess ratios were 102% in Tokyo, 53% in Osaka, 30% in Nagoya and 15% in Chubu mountainous area. These excess causes an underestimate from 3 to 17 years in apparent SF₆ age, suggesting that adjustment of the input air curve is necessary when the SF₆ method is applied to the groundwater dating in Japan.