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| Titel |
Oxidation photochemistry in the Southern Atlantic boundary layer: unexpected deviations of photochemical steady state |
| VerfasserIn |
Z. Hosaynali Beygi, H. Fischer, H. D. Harder, M. Martinez, R. Sander, J. Williams, D. M. Brookes, P. S. Monks, J. Lelieveld  |
| 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 ; 11, no. 16 ; Nr. 11, no. 16 (2011-08-22), S.8497-8513 |
| Datensatznummer |
250010018
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| Publikation (Nr.) |
 copernicus.org/acp-11-8497-2011.pdf |
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| Zusammenfassung |
Ozone (O3) is a photochemical oxidant, an air pollutant and a
greenhouse gas. As the main precursor of the hydroxyl radical (OH) it
strongly affects the oxidation power of the atmosphere. The remote marine
boundary layer (MBL) is considered an important region in terms of chemical
O3 loss; however surface-based atmospheric observations are sparse and
the photochemical processes are not well understood. To investigate the
photochemistry under the clean background conditions of the Southern
Atlantic Ocean, ship measurements of NO, NO2, O3, JNO2,
J(O1D), HO2, OH, ROx and a range of meteorological parameters
were carried out. The concentrations of NO and NO2 measured on board
the French research vessel Marion-Dufresne (28° S–57° S, 46° W–34° E)
in March 2007, are among the lowest yet observed.
The data is evaluated for consistency with photochemical steady state (PSS)
conditions, and the calculations indicate substantial deviations from PSS (Φ>1).
The deviations observed under low NOx conditions (5–25 pptv)
demonstrate a remarkable upward tendency in the Leighton ratio (used to
characterize PSS) with increasing NOx mixing ratio and JNO2
intensity.
It is a paradigm in atmospheric chemistry that OH largely controls the
oxidation efficiency of the atmosphere. However, evidence is growing that
for unpolluted low-NOx (NO + NO2) conditions the atmospheric oxidant
budget is poorly understood. Nevertheless, for the very cleanest conditions,
typical for the remote marine boundary layer, good model agreement with
measured OH and HO2 radicals has been interpreted as accurate
understanding of baseline photochemistry. Here we show that such agreement
can be deceptive and that a yet unidentified oxidant is needed to explain
the photochemical conditions observed at 40°–60° S over the Atlantic
Ocean. |
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