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| Titel |
Improved global modelling of HOx recycling in isoprene oxidation: evaluation against the GABRIEL and INTEX-A aircraft campaign measurements |
| VerfasserIn |
T. Stavrakou, J. Peeters, J.-F. Müller |
| 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. 20 ; Nr. 10, no. 20 (2010-10-19), S.9863-9878 |
| Datensatznummer |
250008839
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| Publikation (Nr.) |
 copernicus.org/acp-10-9863-2010.pdf |
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| Zusammenfassung |
| Stimulated by recent important developments regarding the oxidation chemistry of isoprene, this
study evaluates and quantifies the impacts of different mechanism updates on the boundary
layer concentrations of OH and HO2 radicals using the IMAGESv2 global chemistry transport
model. The model results for HOx, isoprene, NO, and ozone are evaluated against air-based
observations from the GABRIEL campaign, conducted over the Guyanas in October 2005, and
from the INTEX-A campaign over the Eastern US in summer 2004. The version 2 of the Mainz
Isoprene Mechanism (MIM2, Taraborrelli et al., 2009) used as reference mechanism in our
simulations, has been modified to test (i) the artificial OH recycling proposed by
Lelieveld et al. (2008), (ii) the epoxide formation mechanism proposed by Paulot et al. (2009b),
and finally (iii) the HOx regeneration of the Leuven Isoprene Mechanism (LIM0) proposed by
Peeters and Müller (2010). The simulations show that the LIM0 scheme holds by far
the largest potential impact on HOx concentrations over densely vegetated areas in the
Tropics as well as at mid-latitudes. Strong increases, by up to a factor of 4 in the
modelled OH concentrations, and by a factor of 2.5–3 in the HO2 abundances are
estimated through the LIM0 mechanism compared to the traditional isoprene degradation
schemes. Comparatively much smaller OH increases (<25%) are associated with the
implementation of the mechanism of Paulot et al. (2009b); moreover, the global production of
epoxides is strongly suppressed (by a factor of 4) when the LIM0 scheme is combined
with this mechanism. Hydroperoxy-aldehydes (HPALDs) are found to be major first-generation
products in the oxidation of isoprene by OH, with a combined globally averaged yield of 50–60%.
The use of the LIM0 chemistry in the global model allows for reconciling the model with
the observed concentrations at a satisfactory level, compared to the other tested mechanisms,
as the observed averaged mixing ratios of both OH and HO2 in the boundary layer can be
reproduced to within 30%. In spite of the remaining uncertainties in the theoretically-predicted
rates of critical radical reactions leading to the formation of HPALDs, and even more in the
subsequent degradation of these new compounds, the current findings make a strong case for the
newly proposed chemical scheme. Experimental confirmation and quantification
is urgently needed for the formation of HPALDs and for their fast OH-generating photolysis. |
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