Measurements of OH and HO2 concentrations during the MCMA-2006 field campaign – Part 2: Model comparison and radical budget
Item
Title (Dublin Core)
Measurements of OH and HO2 concentrations during the MCMA-2006 field campaign – Part 2: Model comparison and radical budget
Description (Dublin Core)
Measurements of hydroxyl (OH) and hydroperoxy (HO<sub>2</sub>) 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 RO<sub>x</sub> (OH + HO<sub>2</sub> + RO<sub>2</sub>) 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 <i>J</i>-values and the concentrations of 97 chemical species. Several issues related to the RO<sub>x</sub> chemistry under polluted conditions are highlighted in this study: (i) Measured concentrations of both OH and HO<sub>2</sub> 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 HO<sub>2</sub>/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 NO<sub>x</sub> conditions, the HO<sub>2</sub> to OH propagation rate may be overestimated by the model or a process converting OH into HO<sub>2</sub> 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, O<sub>3</sub>-alkene reactions and dicarbonyls photolysis are the main radical sources. O<sub>3</sub> photolysis contributes to less than 6% of the total radical production.
Creator (Dublin Core)
Dusanter, S.
Vimal, D.
Stevens, P. S.
Volkamer, R.
Molina, L. T.
Baker, A.
Meinardi, S.
Blake, D.
Sheehy, P.
Merten, A.
Zhang, R.
Zheng, J.
Fortner, E. C.
Junkermann, W.
Dubey, M.
Rahn, T.
Eichinger, B.
Lewandowski, P.
Prueger, J.
Holder, H.
Date (Dublin Core)
2018-01-15
Type (Dublin Core)
Text
Format (Dublin Core)
application/pdf
Identifier (Dublin Core)
10.5194/acp-9-6655-2009
https://acp.copernicus.org/articles/9/6655/2009/
Source (Dublin Core)
eISSN: 1680-7324
Language (Dublin Core)
eng
