Investigation of the light-enhanced emission of mercury from naturally enriched substrates |
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| Institution: | 1. Department of Environmental and Resources Sciences, University of Nevada-Reno, Reno, NV 89557, USA;2. Institute of Environmental Geochemistry, INF 236, 69120 Heidelberg, Germany;3. Department of Geologic and Environmental Sciences, Stanford University, Stanford, CA 94304-2155, USA;1. Graduate School of Environmental and Life Science, Okayama University, 3-1-1 Tsushima Naka Kita-Ku, Okayama, 700-8530, Japan;2. Graduate School of Engineering, Kyoto University, C-1-3 Nishikyo-ku, Kyoto, 615-8540, Japan;1. State Key Laboratory of Cryospheric Science, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China;2. School of Geography and Tourism, Shaanxi Normal University, Xi’an 710119, China;3. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy Sciences, Xi’an 710061, China;4. University of Chinese Academy of Sciences, Beijing 100049, China;5. CAS Center for Excellence in Tibetan Plateau Earth Science, Beijing 100049, China;6. Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China;1. State Environmental Protection Key Lab of Environmental Risk Assessment and Control on Chemical Processes, East China University of Science and Technology, Shanghai 200237, China;2. Shanghai Key Laboratory of Atmospheric Particle Pollution Prevention, Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, China |
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| Abstract: | Incident radiation has been reported to facilitate mercury release from soils. In this study the influence of light on mercury emissions from substrates amended with pure synthetic mercury species, and from naturally and anthropogenically mercury-enriched substrates were investigated using laboratory experiments and in situ flux measurements. Light-enhanced emissions were found to occur from substrates amended with HgS, and from elemental mercury (Hg0) and HgCl2 amended iron oxide and organic containing substrates. The magnitude of light-enhanced emissions for natural substrates ranged from 1.5 to 116 times that occurring in the dark at the same substrate temperature. Substrates containing corderoite, metacinnabar and “matrix bound mercury” (that bound to organic or inorganic phases) exhibited a higher degree of light-enhanced emissions relative to that containing predominantly cinnabar. Calculated activation energies for both laboratory and field data indicate that photo-reduction is a process associated with the light-enhanced emissions. Activation energies, derived using in situ mercury fluxes and soil temperatures, indicated that photo-reduction was a dominant process facilitating release of Hg from substrates with sunrise. Activation energies, calculated using daytime data, were less than those calculated for sunrise. This is hypothesized to be due to a pool of Hg0 being developed with photo-reduction at first light that is released as soil temperatures and convective heat transfer increase during the day. This study demonstrated that light energy is the more dominant process controlling mercury emissions from naturally enriched substrates than soil temperature. |
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