433-3 A Comprehensive Database of Global Soil-Atmosphere Flux Studies of Mercury.

See more from this Division: SSSA Division: Soil Chemistry
See more from this Session: Mercury in Soils: Patterns and Processes: I (includes student competition)
Wednesday, November 5, 2014: 1:45 PM
Long Beach Convention Center, Room 103C
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Theo Le Dantec1, Yannick Agnan2, Daniel Obrist2 and Chris Moore2, (1)Universite Paul Sabatier / ENSAT, Toulouse, France
(2)Desert Research Institute, Reno, NV
In this study, we built a global database to comprehensively constrain and summarize flux measurements of gaseous elemental mercury (Hg0) between soils and terrestrial environments and the atmosphere. Soils serve as large reservoirs for atmospheric deposition of Hg, but due to the semi-volatile nature of Hg0 and reduction processes, Hg0 can re-emit from terrestrial environment to the atmosphere. Such Hg0 re-emissions, or legacy emissions, are estimated to globally account for up to 60% of current atmospheric Hg loads.

Our analysis of information contained in the database shows that global flux measurements of Hg0 have mainly been conducted in the United States, Europe, and East Asia, with a few additional measurements from South America and Australia. Large areas of the globe are missing information on surface-atmosphere exchange of Hg0, in particular in Africa, Eurasia, and large areas in the northern latitudes. Measurements are strongly biased towards daytime measurements (85%) as compared to nighttime, as well as towards spring and summer measurements (65% of all measurements). We found that bare soils account for over 40% of all terrestrial Hg0 flux measurements, and 57% of all studies were conducted over sites considered to have background soil Hg concentrations. On the other hand, only 40% of all flux measurements were conducted under air Hg concentrations at and near background levels (i.e., <2 ng m-3) showing that a majority of measurements were conducted over sites affected by high Hg levels either due to natural enrichment, mining, or atmospheric contamination. Additionally, there was a large difference in the number of studies using specific techniques for measuring Hg0 flux, with 85% of all studies being conducted with chamber methods with a variety of different designs, materials, and measurement protocols. In contrast, only 15% of fluxes were based on other methods such as micrometeorological techniques.

Fluxes of Hg0 span a wide range of -5,500 ng m-2 hr-1 (i.e., deposition) to + 110,000 ng m-2 hr-1, and fluxes measured before the year 2005 were on average over three times higher than fluxes measured after 2005. This difference is likely due to improvement of measurement techniques and a shift towards more measurements over background areas. Our analysis indicates that to estimate global and regional budgets of surface-atmosphere exchange and their dependence on environmental variables, careful consideration should be given to measurement methods and biases of available data.

See more from this Division: SSSA Division: Soil Chemistry
See more from this Session: Mercury in Soils: Patterns and Processes: I (includes student competition)
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