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| Titel |
An analysis of fast photochemistry over high northern latitudes during spring and summer using in-situ observations from ARCTAS and TOPSE |
| VerfasserIn |
J. R. Olson, J. H. Crawford, W. Brune, J. Mao, X. Ren, A. Fried, B. Anderson, E. Apel, M. Beaver, D. Blake, G. Chen, J. Crounse, J. Dibb, G. Diskin, S. R. Hall, L. G. Huey, D. Knapp, D. Richter, D. Riemer, J. St. Clair, K. Ullmann, J. Walega, P. Weibring, A. Weinheimer, P. Wennberg, A. Wisthaler |
| 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. 15 ; Nr. 12, no. 15 (2012-08-01), S.6799-6825 |
| Datensatznummer |
250011357
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| Publikation (Nr.) |
 copernicus.org/acp-12-6799-2012.pdf |
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| Zusammenfassung |
| Observations of chemical constituents and meteorological quantities obtained
during the two Arctic phases of the airborne campaign ARCTAS (Arctic
Research of the Composition of the Troposphere from Aircraft and Satellites)
are analyzed using an observationally constrained steady state box model.
Measurements of OH and HO2 from the Penn State ATHOS instrument are
compared to model predictions. Forty percent of OH measurements below 2 km
are at the limit of detection during the spring phase (ARCTAS-A). While the
median observed-to-calculated ratio is near one, both the scatter of
observations and the model uncertainty for OH are at the magnitude of
ambient values. During the summer phase (ARCTAS-B), model predictions of OH
are biased low relative to observations and demonstrate a high sensitivity
to the level of uncertainty in NO observations. Predictions of HO2
using observed CH2O and H2O2 as model constraints are up to
a factor of two larger than observed. A temperature-dependent terminal loss
rate of HO2 to aerosol recently proposed in the literature is shown to
be insufficient to reconcile these differences. A comparison of ARCTAS-A to
the high latitude springtime portion of the 2000 TOPSE campaign
(Tropospheric Ozone Production about the Spring Equinox) shows similar
meteorological and chemical environments with the exception of peroxides;
observations of H2O2 during ARCTAS-A were 2.5 to 3 times larger
than those during TOPSE. The cause of this difference in peroxides remains
unresolved and has important implications for the Arctic HOx budget.
Unconstrained model predictions for both phases indicate photochemistry
alone is unable to simultaneously sustain observed levels of CH2O and
H2O2; however when the model is constrained with observed
CH2O, H2O2 predictions from a range of rainout
parameterizations bracket its observations. A mechanism suitable to explain
observed concentrations of CH2O is uncertain. Free tropospheric
observations of acetaldehyde (CH3CHO) are 2–3 times larger than its
predictions, though constraint of the model to those observations is
sufficient to account for less than half of the deficit in predicted
CH2O. The box model calculates gross O3 formation during spring to
maximize from 1–4 km at 0.8 ppbv d−1, in agreement with estimates from
TOPSE, and a gross production of 2–4 ppbv d−1 in the boundary layer and
upper troposphere during summer. Use of the lower observed levels of
HO2 in place of model predictions decreases the gross production by
25–50%. Net O3 production is near zero throughout the ARCTAS-A
troposphere, and is 1–2 ppbv in the boundary layer and upper altitudes
during ARCTAS-B. |
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