15 Sep 2009
15 Sep 2009
Measurements of OH and HO2 concentrations during the MCMA-2006 field campaign – Part 2: Model comparison and radical budget
S. Dusanter1, D. Vimal1,*, P. S. Stevens1, R. Volkamer2, L. T. Molina3,4, A. Baker5, S. Meinardi5, D. Blake5, P. Sheehy3,4, A. Merten6,**, R. Zhang7, J. Zheng7, E. C. Fortner8,***, W. Junkermann9, M. Dubey10, T. Rahn10, B. Eichinger11, P. Lewandowski11, J. Prueger12, and H. Holder13
S. Dusanter et al.
S. Dusanter1, D. Vimal1,*, P. S. Stevens1, R. Volkamer2, L. T. Molina3,4, A. Baker5, S. Meinardi5, D. Blake5, P. Sheehy3,4, A. Merten6,**, R. Zhang7, J. Zheng7, E. C. Fortner8,***, W. Junkermann9, M. Dubey10, T. Rahn10, B. Eichinger11, P. Lewandowski11, J. Prueger12, and H. Holder13
- 1Center for Research in Environmental Science, School of Public and Environmental Affairs, and Department of Chemistry, Indiana University, Bloomington, IN 47405, USA
- 2Department of Chemistry and Biochemistry, University of Colorado, USA
- 3Molina Center for Energy and the Environment USA
- 4Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, USA
- 5University of California, Irvine, 92697 CA, USA
- 6Institute of Environmental Physics, University of Heidelberg, Germany
- 7Department of Atmospheric Sciences, Texas A&M University, USA
- 8Department of Chemistry, Montana State University, USA
- 9Forschungszentrum Karlsruhe, Institute of Meteorology and Climate Research, IMK-IFU, Garmisch-Partenkirchen, Germany
- 10Earth and Environmental Sciences Division, Los Alamos National Laboratory, USA
- 11IIHR-Hydroscience & Engineering, University of Iowa, Iowa City, IA, USA
- 12USDA National Soil Tilth Lab, Ames, IA, USA
- 13Duke University, Durham, NC, USA
- *now at: SRI International, Menlo Park, CA, USA
- **now at: Institute of Applied Photophysics, Dresden University of Technology, Germany
- ***now at: Aerodyne Research Incorporated, 45 Manning Road, Billerica, MA, USA
- 1Center for Research in Environmental Science, School of Public and Environmental Affairs, and Department of Chemistry, Indiana University, Bloomington, IN 47405, USA
- 2Department of Chemistry and Biochemistry, University of Colorado, USA
- 3Molina Center for Energy and the Environment USA
- 4Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, USA
- 5University of California, Irvine, 92697 CA, USA
- 6Institute of Environmental Physics, University of Heidelberg, Germany
- 7Department of Atmospheric Sciences, Texas A&M University, USA
- 8Department of Chemistry, Montana State University, USA
- 9Forschungszentrum Karlsruhe, Institute of Meteorology and Climate Research, IMK-IFU, Garmisch-Partenkirchen, Germany
- 10Earth and Environmental Sciences Division, Los Alamos National Laboratory, USA
- 11IIHR-Hydroscience & Engineering, University of Iowa, Iowa City, IA, USA
- 12USDA National Soil Tilth Lab, Ames, IA, USA
- 13Duke University, Durham, NC, USA
- *now at: SRI International, Menlo Park, CA, USA
- **now at: Institute of Applied Photophysics, Dresden University of Technology, Germany
- ***now at: Aerodyne Research Incorporated, 45 Manning Road, Billerica, MA, USA
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Received: 20 Mar 2009 – Discussion started: 17 Apr 2009 – Revised: 10 Aug 2009 – Accepted: 10 Aug 2009 – Published: 15 Sep 2009
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.
