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| Titel |
Cloud-resolving simulations of mercury scavenging and deposition in thunderstorms |
| VerfasserIn |
U. S. Nair, Y. Wu, C. D. Holmes, A. Schure, G. Kallos, J. T. Walters |
| 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 ; 13, no. 19 ; Nr. 13, no. 19 (2013-10-15), S.10143-10157 |
| Datensatznummer |
250085753
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| Publikation (Nr.) |
 copernicus.org/acp-13-10143-2013.pdf |
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| Zusammenfassung |
| This study examines dynamical and microphysical features of convective
clouds that affect mercury (Hg) wet scavenging and concentrations in
rainfall. Using idealized numerical model simulations in the Regional
Atmospheric Modeling System (RAMS), we diagnose vertical transport and
scavenging of soluble Hg species – gaseous oxidized mercury (GOM) and
particle-bound mercury (HgP), collectively Hg(II) – in thunderstorms under
typical environmental conditions found in the Northeast and Southeast United
States (US). Mercury scavenging efficiencies from various initial altitudes
are diagnosed for a case study of a typical strong convective storm in the
Southeast US. Assuming that soluble mercury concentrations are initially
vertically uniform, the model results suggest that 60% of mercury
deposited to the surface in rainwater originates from above the boundary
layer (> 2 km). The free troposphere could supply a larger
fraction of mercury wet deposition if GOM and HgP concentrations increase
with altitude. We use radiosonde observations in the Northeast and Southeast
to characterize three important environmental characteristics that influence
thunderstorm morphology: convective available potential energy (CAPE),
vertical shear (0–6 km) of horizontal wind (SHEAR) and precipitable water
(PW). The Southeast US generally has lower SHEAR and higher CAPE and PW. We
then use RAMS to test how PW and SHEAR impact mercury scavenging and
deposition, while keeping the initial Hg(II) concentrations fixed in all
experiments. We found that the mercury concentration in rainfall is
sensitive to SHEAR with the nature of sensitivity differing depending upon
the PW. Since CAPE and PW cannot be perturbed independently, we test their
combined influence using an ensemble of thunderstorm simulations initialized
with environmental conditions for the Northeast and Southeast US. These
simulations, which begin with identical Hg(II) concentrations, predict
higher mercury concentrations in rainfall from thunderstorms forming in the
environmental conditions over the Southeast US compared to the Northeast US.
A final simulation of a stratiform rain event produces lower mercury
concentrations than in thunderstorms forming in environments typical of the
Southeast US. The stratiform cloud scavenges mercury from the lowest
~ 4 km of the atmosphere, while thunderstorms scavenge up to
~ 10 km. |
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