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| Titel |
Observations of OH and HO2 radicals over West Africa |
| VerfasserIn |
R. Commane, C. F. A. Floquet, T. Ingham, D. Stone, M. J. Evans, D. E. Heard |
| 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 ; 10, no. 18 ; Nr. 10, no. 18 (2010-09-17), S.8783-8801 |
| Datensatznummer |
250008779
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| Publikation (Nr.) |
 copernicus.org/acp-10-8783-2010.pdf |
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| Zusammenfassung |
| The hydroxyl radical (OH) plays a key role in the oxidation of trace gases in
the troposphere. However, observations of OH and the closely related
hydroperoxy radical (HO2) have been sparse, especially in the tropics.
Based on a low-pressure laser-induced fluorescence technique (FAGE –
Fluorescence Assay by Gas Expansion), an instrument has been developed to
measure OH and HO2 aboard the Facility for Airborne Atmospheric
Measurement (FAAM) BAe-146 research aircraft. During the African Monsoon
Multidisciplinary Analyses (AMMA) campaign, observations of OH and HO2
(HOx) were made in the boundary layer and free troposphere over West
Africa on 13 flights during July and August 2006. Mixing ratios of both OH
and HO2 were found to be highly variable, but followed a diurnal cycle:
OH varied from 1.3 pptv to below the instrumental limit of detection, with
a median mixing ratio of 0.17 pptv. HO2 varied from 42.7 pptv to
below the limit of detection, with a median mixing ratio of 8.0 pptv. A
median HO2/OH ratio of 95 was observed. Daytime OH observations were
compared with the primary production rate of OH from ozone photolysis in the
presence of water vapour. Daytime HO2 observations were generally
reproduced by a simple steady-state HOx calculation, where HOx was assumed to be formed from the primary production of OH and lost
through HO2 self-reaction. Deviations between the observations and this
simple model were found to be grouped into a number of specific cases: (a)
within cloud, (b) in the presence of high levels of isoprene in the boundary
layer and (c) within a biomass burning plume. HO2 was sampled in and
around cloud, with significant short-lived reductions of HO2 observed.
Up to 9 pptv of HO2 was observed at night, with HO2 above 6 pptv
observed at altitudes above 6 km. In the forested boundary layer, HO2
was underestimated by a steady state calculation at altitudes below
500 m but overestimated between 500 m and 2 km. In a biomass burning
plume, observed HO2 concentrations were significantly below those
calculated. |
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