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| Titel |
The diurnal variability of atmospheric nitrogen oxides (NO and NO2) above the Antarctic Plateau driven by atmospheric stability and snow emissions |
| VerfasserIn |
M. M. Frey, N. Brough, J. L. France, P. S. Anderson, O. Traullé, M. D. King, A. E. Jones, E. W. Wolff, J. Savarino |
| 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. 6 ; Nr. 13, no. 6 (2013-03-15), S.3045-3062 |
| Datensatznummer |
250018517
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| Publikation (Nr.) |
 copernicus.org/acp-13-3045-2013.pdf |
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| Zusammenfassung |
| Atmospheric nitrogen oxides (NO and NO2) were
observed at Dome C, East Antarctica (75.1° S,
123.3° E, 3233 m), for a total of 50 days, from 10 December
2009 to 28 January 2010. Average (±1σ) mixing ratios at 1.0 m
of NO and NO2, the latter measured for the first time
on the East Antarctic Plateau, were 111 (±89) and 98
(±89) pptv, respectively. Atmospheric mixing ratios are on
average comparable to those observed previously at South Pole, but
in contrast show strong diurnal variability: a minimum around local noon
and a maximum in the early evening coincide with the development
and collapse of a convective boundary layer. The asymmetric diurnal
cycle of NOx concentrations and likely any other chemical tracer with
a photolytic surface source is driven by the turbulent diffusivity and height
of the atmospheric boundary layer, with the former controlling the magnitude
of the vertical flux and the latter the size of the volume into which snow emissions
are transported. In particular, the average (±1σ) NOx
emission flux from 22 December 2009 to 28 January 2010, estimated from
atmospheric concentration gradients, was 8.2 (±7.4) × 1012 molecule m−2 s−1
belongs to the largest values measured so far in the polar regions and explains
the 3-fold increase in mixing ratios in the early evening when the boundary layer
becomes very shallow. Dome C is likely not representative for the entire East
Antarctic Plateau but illustrates the need of an accurate description of the
boundary layer above snow in atmospheric chemistry models. A simple nitrate
photolysis model matches the observed median diurnal NOx
flux during the day but has significant low bias during the night. The difference
is significant taking into account the total random error in flux observations and
model uncertainties due to the variability of NO3− concentrations in
snow and potential contributions from NO2− photolysis. This highlights
uncertainties in the parameterization of the photolytic NOx source in natural
snowpacks, such as the poorly constrained quantum yield of nitrate photolysis.
A steady-state analysis of the NO2 : NO ratios indicates that
peroxy (HO2 + RO2) or other radical concentrations in the boundary layer
of Dome C are either higher than measured elsewhere in the polar regions or
other processes leading to enhanced NO2 have to be invoked. These
results confirm the existence of a strongly oxidising canopy enveloping the East
Antarctic Plateau in summer. |
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