Measurements Of Reactive Gaseous Mercury Using Laser–Based Spectroscopic Techniques

A detailed understanding of the role of mercury (Hg) in ecosystems is a critical issue from a human health perspective, particularly regarding the ingestion of methyl-mercury from contaminated fish. The atmospheric Hg burden has increased by a factor of three in the past one hundred years primarily due to anthropogenic input. Atmospheric Hg exists principally in its elemental form, Hg(0), which, until recently, was thought to be unreactive in the gas phase.  Hg(0) is insoluble in water and has a low deposition rate. In contrast, oxidized Hg, typically referred to as RGM (reactive gaseous mercury), is soluble and appears to be efficiently removed from the atmosphere by both wet and dry deposition, therefore increasing Hg contamination. Although the CVAFS (cold vapour atomic fluorescence spectroscopy) approach is well established for measurement of Hg0, no measurement technique has shown the combination of sensitivity, temporal resolution and precision necessary for direct measurement of Hg0 fluxes. We are developing experimental approaches using both sequential two photon and single photon laser induced fluorescence (LIF) that are designed to address some of these issues. During our recent flight experiment, we used both KCl coated annular denuders and uncoated etched tubular denuders along with a Tekran 2537B mercury analyzer over the S.E. United States collecting and analyzing air samples. Analyses are still ongoing, but consistent structures at multiple variables are being initially observed giving us the preliminary impression that Hg levels are being identified.  Following this project, more calibrations will be performed to fully analyze our data.