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Estimation of Hg⁰ exchange between ecosystems and the atmosphere using ²²²RN and Hg⁰ concentration changes in the stable nocturnal boundary layer

Obrist, D. and Conen, F. and Vogt, R. and Siegwolf, R. and Alewell, C.. (2006) Estimation of Hg⁰ exchange between ecosystems and the atmosphere using ²²²RN and Hg⁰ concentration changes in the stable nocturnal boundary layer. Atmospheric environment, Vol. 40 , H. 5. pp. 856-866.

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Official URL: http://edoc.unibas.ch/dok/A5251158

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Abstract

The goal of this study was to test a Rn-222/Hg-0 method to measure exchange fluxes of Hg-0 between ecosystems and the atmosphere complementing gradient-based micrometeorological methods which are difficult to apply when exchange fluxes are very low, during calm nights, and over heterogeneous surfaces. The method is based on absolute concentration changes of Hg-0 and of the trace gas Rn-222 over several hours in the stable nocturnal boundary layer (NBL) when absolute gas concentrations change according to the source or sink strength of the underlying landscape. 222Rn accumulations were observed in 28 of 66 measured nights in an urban area and in 14 of the 40 nights at a subalpine grassland. Concurrent and significant increases in atmospheric Hg-0 concentrations were observed 22 times in the urban area and calculated Hg-0 emissions-for the first time measured over a city area-averaged 6.4 +/- 0.9 ng m(-2) h(-1). Concurrent changes in Hg-0 in the stable NBLs at the subalpine site were very small and significant only nine times with calculated Hgo fluxes averaging -0.2 +/- 0.3 ng m(-2) h(-1), indicating that the flux of Hg-0 in the grassland was a very small net deposition of atmospheric Hg-0 to the ecosystem. At the subalpine grassland the Rn-222/Hg-0 method compared reasonably well to a modified Bowen ratio (MBR) method applied during turbulent conditions (-1.9 +/- 0.2 ng m(-2) h(-1) [or -1.7 +/- 0.4 ng m(-2) h(-1) during nights only]). The MBR, however, was not applicable in the urban area due to high surface roughness. We conclude that the Rn-222/Hg-0 method-although limited to nighttime periods in our study-can complement gradient-based methods during stable NBL periods and can be used over heterogeneous surfaces when conventional micrometeorological approaches are not applicable. (c) 2005 Elsevier Ltd. All rights reserved.
Faculties and Departments:05 Faculty of Science > Departement Umweltwissenschaften > Meteorologie, Klimatologie und Fernerkundung > Meteorologie (Parlow)
05 Faculty of Science > Departement Umweltwissenschaften > Umweltgeowissenschaften > Umweltgeowissenschaften (Alewell)
UniBasel Contributors:Vogt, Roland and Alewell, Christine
Item Type:Article, refereed
Article Subtype:Research Article
Bibsysno:Link to catalogue
Publisher:Elsevier
ISSN:1352-2310
Note:Publication type according to Uni Basel Research Database: Journal article
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Last Modified:05 Dec 2014 09:45
Deposited On:22 Mar 2012 14:18

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