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Article Dans Une Revue (Article De Synthèse) Atmospheric Chemistry and Physics Année : 2009

Measurements of OH and HO<sub>2</sub> concentrations during the MCMA-2006 field campaign – Part 2: Model comparison and radical budget

D. Vimal
  • Fonction : Auteur
P. Stevens
  • Fonction : Auteur
R. Volkamer
  • Fonction : Auteur
L. Molina
  • Fonction : Auteur
A. Baker
  • Fonction : Auteur
S. Meinardi
  • Fonction : Auteur
D. Blake
  • Fonction : Auteur
P. Sheehy
  • Fonction : Auteur
A. Merten
  • Fonction : Auteur
R. Zhang
  • Fonction : Auteur
J. Zheng
  • Fonction : Auteur
E. Fortner
  • Fonction : Auteur
W. Junkermann
  • Fonction : Auteur
M. Dubey
  • Fonction : Auteur
T. Rahn
  • Fonction : Auteur
B. Eichinger
  • Fonction : Auteur
P. Lewandowski
  • Fonction : Auteur
J. Prueger
  • Fonction : Auteur
H. Holder
  • Fonction : Auteur

Résumé

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.

Dates et versions

hal-04249429 , version 1 (19-10-2023)

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Citer

Sébastien Dusanter, D. Vimal, P. Stevens, R. Volkamer, L. Molina, et al.. Measurements of OH and HO<sub>2</sub> concentrations during the MCMA-2006 field campaign – Part 2: Model comparison and radical budget. Atmospheric Chemistry and Physics, 2009, 9 (18), pp.6655-6675. ⟨10.5194/acp-9-6655-2009⟩. ⟨hal-04249429⟩
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