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| Titel |
Measurements of OH and HO2 concentrations during the MCMA-2006 field campaign – Part 2: Model comparison and radical budget |
| VerfasserIn |
S. Dusanter, D. Vimal, P. S. Stevens, R. Volkamer, L. T. Molina, A. Baker, S. Meinardi, D. Blake, P. Sheehy, A. Merten, R. Zhang, J. Zheng, E. C. Fortner, W. Junkermann, M. Dubey, T. Rahn, B. Eichinger, P. Lewandowski, J. Prueger, Heidi Holder |
| 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 ; 9, no. 18 ; Nr. 9, no. 18 (2009-09-15), S.6655-6675 |
| Datensatznummer |
250007624
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| Publikation (Nr.) |
 copernicus.org/acp-9-6655-2009.pdf |
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| Zusammenfassung |
| Measurements of hydroxyl (OH) and hydroperoxy (HO2) radicals were made
during the Mexico City Metropolitan Area (MCMA) field campaign as part of
the MILAGRO (Megacity Initiative: Local and Global Research Observations)
project during March 2006. These measurements provide a unique opportunity
to test current models of atmospheric ROx (OH + HO2 + RO2)
photochemistry under polluted conditions. A zero-dimensional box model based
on the Regional Atmospheric Chemical Mechanism (RACM) was constrained by
10-min averages of 24 J-values and the concentrations of 97 chemical
species. Several issues related to the ROx chemistry under polluted
conditions are highlighted in this study: (i) Measured concentrations of
both OH and HO2 were underpredicted during morning hours on a median
campaign basis, suggesting a significant source of radicals is missing from
current atmospheric models under polluted conditions, consistent with
previous urban field campaigns. (ii) The model-predicted HO2/OH ratios
underestimate the measurements for NO mixing ratios higher than 5 ppb, also
consistent with previous urban field campaigns. This suggests that under
high NOx conditions, the HO2 to OH propagation rate may be
overestimated by the model or a process converting OH into HO2 may be
missing from the chemical mechanism. On a daily basis (08:40 a.m.–06:40 p.m.),
an analysis of the radical budget indicates that HONO photolysis, HCHO
photolysis, O3-alkene reactions and dicarbonyls photolysis are the main
radical sources. O3 photolysis contributes to less than 6% of the
total radical production. |
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