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| Titel |
Radical budget analysis in a suburban European site during the MEGAPOLI summer field campaign |
| VerfasserIn |
V. Michoud, A. Kukui, M. Camredon, A. Colomb, A. Borbon, K. Miet, B. Aumont, M. Beekmann, R. Durand-Jolibois, S. Perrier, P. Zapf, G. Siour, W. Ait-Helal, N. Locoge, S. Sauvage, C. Afif, V. Gros, M. Furger, G. Ancellet, J. F. Doussin |
| 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. 24 ; Nr. 12, no. 24 (2012-12-17), S.11951-11974 |
| Datensatznummer |
250011673
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| Publikation (Nr.) |
 copernicus.org/acp-12-11951-2012.pdf |
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| Zusammenfassung |
| Chemical Ionisation Mass Spectrometer measurements of hydroxyl radical (OH)
and the sum of hydroperoxy and organic peroxy (HO2+RO2) radicals
were conducted during the MEGAPOLI summer field campaign at the SIRTA
observatory near Paris, France, in July 2009. OH and (HO2+RO2)
showed a typical diurnal variation with averaged daytime maxima values
around 5×106 and 1.2×108 molecule cm−3, respectively.
Simultaneously, a large number of ancillary measurements, such as NOx,
O3, HONO, HCHO and other VOCs were also conducted. These data provide
an opportunity to assess our understanding of the radical chemistry in a
suburban environment by comparing the radical observations to calculations.
First, OH mixing ratios were estimated by a simple Photo Stationary State
(PSS) calculation. PSS calculations overestimate the OH mixing ratio by
50%, especially at NOx mixing ratios lower than 10 ppb, suggesting
that some loss processes were missing in the calculation at low NOx.
Then, a photochemical box model simulation based on the Master Chemical
Mechanism (MCM) and constrained by ancillary measurements was run to
calculate radical concentrations. Three different modelling procedures were
tested, varying the way the unconstrained secondary species were estimated,
to cope with the unavoidable lack of their measurements. They led to
significant differences in simulated radical concentrations. OH and
(HO2+RO2) concentrations estimated by two selected model version
were compared with measurements. These versions of the model were chosen
because they lead, respectively, to the higher and lower simulated radical
concentrations and are thus the two extremes versions. The box model showed
better results than PSS calculations, with a slight overestimation of 12%
and 5%, for OH and (HO2+RO2) respectively, in average for the
reference model, and an overestimation of approximately 20% for OH and an
underestimation for (HO2+RO2) for the other selected model
version. Thus, we can conclude from our study that OH and
(HO2+RO2) radical levels agree on average with observations
within the uncertainty range. Finally, an analysis of the radical budget, on
a daily basis (06:00–18:00 UTC), indicates that HONO photolysis
(~35%), O3 photolysis (~23%), and
aldehydes and ketones photolysis (~16% for formaldehyde
and 18% for others) are the main radical initiation pathways. According
to the MCM modelling, the reactions of RO2 with NO2
(~19%), leading mainly to PAN formation, is a significant
termination pathway in addition to the main net loss via reaction of OH with
NO2 (~50%). |
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