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| Titel |
Use of a global model to understand speciated atmospheric mercury observations at five high-elevation sites |
| VerfasserIn |
P. Weiss-Penzias, H. M. Amos, N. E. Selin, Mae Sexauer Gustin, D. A. Jaffe, D. Obrist, G.-R. Sheu, A. Giang |
| 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 ; 15, no. 3 ; Nr. 15, no. 3 (2015-02-02), S.1161-1173 |
| Datensatznummer |
250119383
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| Publikation (Nr.) |
 copernicus.org/acp-15-1161-2015.pdf |
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| Zusammenfassung |
| Atmospheric mercury (Hg) measurements using the
Tekran® analytical system from five
high-elevation sites (1400–3200 m elevation), one in Asia and four in the
western US, were compiled over multiple seasons and years, and these data
were compared with the GEOS-Chem global model. Mercury data consisted of
gaseous elemental Hg (GEM) and "reactive Hg" (RM), which is a combination
of the gaseous oxidized (GOM) and particulate bound
(< 2.5 μm) (PBM) fractions as measured by the
Tekran® system. We used a subset of the
observations by defining a "free tropospheric" (FT) data set by screening
using measured water vapor mixing ratios. The oxidation scheme used by the
GEOS-Chem model was varied between the standard run with Br oxidation and an
alternative run with OH–O3 oxidation. We used this model–measurement
comparison to help interpret the spatio-temporal trends in, and relationships
among, the Hg species and ancillary parameters, to understand better the
sources and fate of atmospheric RM. The most salient feature of the data
across sites, seen more in summer relative to spring, was that RM was
negatively correlated with GEM and water vapor mixing ratios (WV) and
positively correlated with ozone (O3), both in the standard model and
the observations, indicating that RM was formed in dry upper altitude air
from the photo-oxidation of GEM. During a free tropospheric transport high RM
event observed sequentially at three sites from Oregon to Nevada, the slope
of the RM / GEM relationship at the westernmost site was
−1020 ± 209 pg ng−1, indicating near-quantitative GEM-to-RM
photochemical conversion. An improved correlation between the observations
and the model was seen when the model was run with the OH–O3 oxidation
scheme instead of the Br oxidation scheme. This simulation produced higher
concentrations of RM and lower concentrations of GEM, especially at the
desert sites in northwestern Nevada. This suggests that future work should
investigate the effect of Br- and O3-initiated gas-phase oxidation
occurring simultaneously in the atmosphere, as well as aqueous and
heterogeneous reactions to understand whether there are multiple global
oxidants for GEM and hence multiple forms of RM in the atmosphere. If the
chemical forms of RM were known, then the collection efficiency of the
analytical method could be evaluated better. |
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