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| Titel |
High levels of reactive gaseous mercury observed at a high elevation research laboratory in the Rocky Mountains |
| VerfasserIn |
X. Faïn, D. Obrist, A. G. Hallar, I. Mccubbin, T. Rahn |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 9, no. 20 ; Nr. 9, no. 20 (2009-10-23), S.8049-8060 |
| Datensatznummer |
250007709
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| Publikation (Nr.) |
 copernicus.org/acp-9-8049-2009.pdf |
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| Zusammenfassung |
| The chemical cycling and spatiotemporal distribution of mercury in the
troposphere is poorly understood. We measured gaseous elemental mercury
(GEM), reactive gaseous mercury (RGM) and particulate mercury (HgP)
along with carbon monoxide (CO), ozone (O3), aerosols, and
meteorological variables at Storm Peak Laboratory at an elevation of 3200 m
a.s.l., in Colorado, from 28 April to 1 July 2008. The mean mercury
concentrations were 1.6 ng m−3 (GEM), 20 pg
m−3 (RGM) and 9 pg m−3
(HgP). We observed eight events of strongly enhanced
atmospheric RGM levels with maximum concentrations up to 137 pg m−3.
RGM enhancement events lasted for long time periods of 2 to 6 days showing
both enriched level during daytime and nighttime when other tracers (e.g.,
aerosols) showed different representations of boundary layer air and free
tropospheric air. During seven of these events, RGM was inversely correlated
to GEM (RGM/GEM regression slope ~−0.1), but did not exhibit
correlations with ozone, carbon monoxide, or aerosol concentrations.
Relative humidity was the dominant factor affecting RGM levels with high RGM
levels always present whenever relative humidity was below 40 to 50%. We
conclude that RGM enhancements observed at Storm Peak Laboratory were not
induced by pollution events and were related to oxidation of tropospheric
GEM. High RGM levels were not limited to upper tropospheric or
stratospherically influenced air masses, indicating that entrainment
processes and deep vertical mixing of free tropospheric air enriched in RGM
may lead to high RGM levels throughout the troposphere and into the boundary
layer over the Western United States. Based on backtrajectory analysis and a
lack of mass balance between RGM and GEM, atmospheric production of RGM may
also have occurred in some distance allowing for scavenging and/or
deposition of RGM prior to reaching the laboratory. Our observations provide
evidence that the tropospheric pool of mercury is frequently enriched in
divalent mercury, that high RGM levels are not limited to upper tropospheric
air masses, but that the build-up of high RGM in the troposphere is limited
to the presence of dry air. |
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