Abstract
In order to clarify the dynamics of atmospheric mercury in the free troposphere, total gaseous mercury (TGM) monitors were installed at the Norikura Observatory (former Norikura Solar Observatory; 2,876 m a.s.l, 36°06′49″N, 137°33′19″E) located at the border between Nagano Prefecture and Gifu Prefecture. The observation conducted in October 2012 and September 2017. The average water vapor mixing ratio (WV) calculated from the radiosonde dataset at the same atmospheric pressure of Wajima and Shirahama meteorological station has been compared with the dataset which was obtained at Norikura Observatory. We observed some boundary layer/upslope flow during daytime, which produced a 26–205％ and a 44–175％ higher WV compared to radiosonde data taken from similar altitudes at the Wajima and the Shirahama meteorological station. Compared to the high WV period, subsided air masses with low WV period contained a relatively low concentration of TGM. Result from the average diurnal change of TGM concentration and WV, the increasing of TGM concentration in day time was observed. The backward trajectory analysis (duration time of 121 hours) at the high TGM concentration events in October 7, 2012 (#1) and September 15, 2017 (#2), were carried out every 100 from 100 to 3,000 m altitude at latitude and longitude of the Norikura Observatory. The air mass residence time of high mercury emission regions in Mainland China occupied 60 and 65％ of the total duration time in #1 and #2 events, respectively. The air masses which were observed high TGM concentration at Norikura observatory come from the high mercury emission regions with relatively long residence time.
