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Measurements of OH and HO2 concentrations during the MCMA-2006 field campaign – Part 2: Model comparison and radical budget

Author(s)
Dusanter, S.; Vimal, D.; Stevens, P. S.; Volkamer, R.; Molina, Luisa Tan; Baker, A.; Meinardi, S.; Blake, D.; Merten, A.; Zhang, R.; Zheng, J.; Fortner, E. C.; Junkermann, W.; Dubey, Madan; Rahn, T.; Eichinger, B.; Lewandowski, P.; Prueger, J.; Holder, H.; Sheehy, P. M.; ... Show more Show less
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Abstract
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.
Date issued
2009-09
URI
http://hdl.handle.net/1721.1/67896
Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
Journal
Atmospheric Chemistry and Physics
Publisher
Copernicus Publications on behalf of the European Geosciences Union
Citation
Dusanter, S. et al. “Measurements of OH and HO2 concentrations during the MCMA-2006 field campaign – Part 2: Model comparison and radical budget.” Atmospheric Chemistry and Physics 9.18 (2009): 6655-6675.
Version: Final published version
ISSN
1680-7324
1680-7316

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