Seasonal change and vertical movement of atmospheric mercury at Kagoshima city in relation with Sakurajima Volcano, Japan

The atmospheric concentration of mercury was determined daily for 3 years (July 1999–March 2002) in Kagoshima City to clarify the seasonal variation of mercury levels and the influence of mercury emitted from Sakurajima. The atmospheric mercury was collected on a porous gold collector at Kagoshima University approximately 11 km west of Sakurajima and the amount of mercury was determined by cold vapor atomic absorption spectrometry (CVAAS). A loss of temperature dependency was found for the east wind in 1999. However, in 2001, high temperature dependency was observed for all wind directions with the easing of volcanic activity. Short-term movement in the atmospheric concentration of mercury was also investigated by making measurements every two hours over a three-day period at heights of 3 and 12 m. This operation was carried out about every two months in the year 2001 at Kagoshima University. The atmospheric mercury concentration was higher in the daytime than nighttime showing temperature dependency: the concentration at 3 m (Hg(3m)) ranged from 1.65 to 17.9 ng m–3 (5.96 ± 3.47 ng m–3) in the daytime and 1.50 to 12.8 ng m–3 (4.20 ± 2.33 ng m–3) overnight, while that at 12 m (Hg(12m)) ranged from 1.24 to 29.4 ng m –3 (4.74 ± 3.61 ng m–3) and 1.38 to 14.8 ng m–3 (4.50 ± 2.85 ng m–3), respectively. The variation in Hg(3m) from day to night was considerably larger than that in Hg(12m). As a result, Hg(3m) was higher than Hg(12m) in the daytime and lower in the nighttime. On the other hand, the concentration gradient showed a high degree of dependency on solar radiation. These observations suggested that mercury is emitted from the ground with an increase in solar radiation and rise of the temperature in the daytime and deposits with the fall of temperature at nighttime. The influence of rain and volcanic activity on the periodic variation of mercury is also discussed in detail.