Process studies on mercury fluxes over different soils with a Laboratory Flux Measurement System (LFMS)

Abstract
A Laboratory Flux chamber System (LFCS) for process studies of the air/surface exchange of mercury was developed. First results of flux studies for a variety of different soils will be presented. The system allows investigating and controlling environmental variables that are thought to influence air/surface exchange processes, SUCH as sunlight, air and soil temperature, air and soil humidity and turbulence conditions as well as physicochemical conditions of the soil. The achievable detection limit for Total Gaseous Mercury (TGM) fluxes defined as is 0,02 ng/m ²/h. For all soils under investigation we found a strong influence of radiation, soil-surface temperature and turbulence on the momentum emission flux of mercury. Temperature differences between the soil surface and the air above showed a moderate but still significant influence on the emission fluxes. First studies focusing on the influence of soil moisture on mercury fluxes indicate, a decrease in mercury fluxes with decreasing soil moisture. This effect seems to be more likely correlated with the soil moisture tension than the soil moisture content. Clear evidence for a photoinduced increase in mercury fluxes for all soils could be revealed. Comparison of measured and calculated fluxes (Figure 1, next page) derived from the temperature dependency of the mercury flux (F-TGM = , x=T[ °C] ) showed good agreement for "dark-phases" but fails for "light"-phases within this time series. This observation is probably due to an additional and enhanced photoinduced emission flux of mercury during radiation phases. Our results suggest, that for a given soil variations in mercury emissions fluxes can be explained by variations in soil surface temperature, turbulence and radiation. A comparison of the fluxes obtained for different soils indicate that the differences in fluxes are well correlated with the mercury concentrations in the soils.