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| Titel |
Modeling chemistry in and above snow at Summit, Greenland – Part 2: Impact of snowpack chemistry on the oxidation capacity of the boundary layer |
| VerfasserIn |
J. L. Thomas, J. E. Dibb, L. G. Huey, J. Liao, D. Tanner, B. Lefer, R. Glasow, J. Stutz |
| 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 ; 12, no. 14 ; Nr. 12, no. 14 (2012-07-25), S.6537-6554 |
| Datensatznummer |
250011342
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| Publikation (Nr.) |
 copernicus.org/acp-12-6537-2012.pdf |
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| Zusammenfassung |
| The chemical composition of the boundary layer in snow covered regions is
impacted by chemistry in the snowpack via uptake, processing, and emission of
atmospheric trace gases. We use the coupled one-dimensional (1-D) snow
chemistry and atmospheric boundary layer model MISTRA-SNOW to study the
impact of snowpack chemistry on the oxidation capacity of the boundary layer.
The model includes gas phase photochemistry and chemical reactions both in
the interstitial air and the atmosphere. While it is acknowledged that the chemistry
occurring at ice surfaces may consist of a true quasi-liquid layer and/or a concentrated
brine layer, lack of additional knowledge requires that this chemistry be modeled as primarily
aqueous chemistry occurring in a liquid-like layer (LLL) on snow grains. The model
has been recently compared with BrO
and NO data taken on 10 June–13 June 2008 as part of the Greenland
Summit Halogen-HOx experiment (GSHOX). In the present study, we use
the same focus period to investigate the influence of snowpack derived
chemistry on OH and HOx + RO2 in the boundary layer.
We compare model results with chemical ionization mass spectrometry (CIMS)
measurements of the hydroxyl radical (OH) and of the hydroperoxyl
radical (HO2) plus the sum of all organic peroxy radicals
(RO2) taken at Summit during summer 2008. Using sensitivity runs we
show that snowpack influenced nitrogen cycling and bromine chemistry both
increase the oxidation capacity of the boundary layer and that together they
increase the mid-day OH concentrations.
Bromine chemistry increases the OH concentration by 10–18% (10% at
noon LT), while snow sourced NOx increases OH concentrations by 20–50% (27% at noon LT).
We show for the first time, using a coupled one-dimensional
snowpack-boundary layer model, that air-snow interactions impact the
oxidation capacity of the boundary layer and that it is not possible to match
measured OH levels without snowpack NOx and halogen emissions. Model
predicted HONO compared with mistchamber measurements suggests there
may be an unknown \chem{HONO} source at Summit. Other model predicted
HOx precursors, H2O2 and HCHO, compare well with
measurements taken in summer 2000, which had lower levels than other years.
Over 3 days, snow sourced NOx
contributes an additional 2 ppb to boundary layer ozone production,
while snow sourced bromine has the opposite effect and contributes
1 ppb to boundary layer ozone loss. |
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