 |
| Titel |
The chemistry of OH and HO2 radicals in the boundary layer over the tropical Atlantic Ocean |
| VerfasserIn |
L. K. Whalley, K. L. Furneaux, A. Goddard, J. D. Lee, A. Mahajan, H. Oetjen, K. A. Read, N. Kaaden, L. J. Carpenter, A. C. Lewis, J. M. C. Plane, E. S. Saltzman, A. Wiedensohler, D. E. Heard |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 10, no. 4 ; Nr. 10, no. 4 (2010-02-15), S.1555-1576 |
| Datensatznummer |
250008102
|
| Publikation (Nr.) |
 copernicus.org/acp-10-1555-2010.pdf |
|
|
|
|
|
| Zusammenfassung |
| Fluorescence Assay by Gas Expansion (FAGE) has been used to detect ambient
levels of OH and HO2 radicals at the Cape Verde Atmospheric
Observatory, located in the tropical Atlantic marine boundary layer, during
May and June 2007. Midday radical concentrations were high, with maximum
concentrations of 9 ×106 molecule cm−3 and
6×108 molecule cm−3 observed for OH and HO2, respectively. A
box model incorporating the detailed Master Chemical Mechanism, extended to
include halogen chemistry, heterogeneous loss processes and constrained by
all available measurements including halogen and nitrogen oxides, has been
used to assess the chemical and physical parameters controlling the radical
chemistry. The model was able to reproduce the daytime radical
concentrations to within the 1 σ measurement uncertainty of 20%
during the latter half of the measurement period but significantly
under-predicted [HO2] by 39% during the first half of the project.
Sensitivity analyses demonstrate that elevated [HCHO] (~2 ppbv) on
specific days during the early part of the project, which were much greater
than the mean [HCHO] (328 pptv) used to constrain the model, could account
for a large portion of the discrepancy between modelled and measured
[HO2] at this time. IO and BrO, although present only at a few pptv,
constituted ~19% of the instantaneous sinks for HO2, whilst
aerosol uptake and surface deposition to the ocean accounted for a further
23% of the HO2 loss at noon. Photolysis of HOI and HOBr accounted
for ~13% of the instantaneous OH formation. Taking into account
that halogen oxides increase the oxidation of NOx (NO → NO2),
and in turn reduce the rate of formation of OH from the reaction of HO2
with NO, OH concentrations were estimated to be 9% higher overall due to
the presence of halogens. The increase in modelled OH from halogen chemistry
gives an estimated 9% shorter lifetime for methane in this region, and
the inclusion of halogen chemistry is necessary to model the observed daily
cycle of O3 destruction that is observed at the surface. Due to surface
losses, we hypothesise that HO2 concentrations increase with height and
therefore contribute a larger fraction of the O3 destruction than at the
surface. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|