ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-9-6655-2009 Measurements of OH and HO<sub>2</sub> concentrations during the MCMA-2006 field campaign – Part 2: Model comparison and radical budget Dusanter S. 1 Vimal D. 1 14 Stevens P. S. 1 Volkamer R. 2 Molina L. T. 3 4 Baker A. 5 Meinardi S. 5 Blake D. 5 Sheehy P. 3 4 Merten A. 6 15 Zhang R. 7 Zheng J. 7 Fortner E. C. 8 16 Junkermann W. 9 Dubey M. 10 Rahn T. 10 Eichinger B. 11 Lewandowski P. 11 Prueger J. 12 Holder H. 13 Center for Research in Environmental Science, School of Public and Environmental Affairs, and Department of Chemistry, Indiana University, Bloomington, IN 47405, USA Department of Chemistry and Biochemistry, University of Colorado, USA Molina Center for Energy and the Environment USA Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, USA University of California, Irvine, 92697 CA, USA Institute of Environmental Physics, University of Heidelberg, Germany Department of Atmospheric Sciences, Texas A&M University, USA Department of Chemistry, Montana State University, USA Forschungszentrum Karlsruhe, Institute of Meteorology and Climate Research, IMK-IFU, Garmisch-Partenkirchen, Germany Earth and Environmental Sciences Division, Los Alamos National Laboratory, USA IIHR-Hydroscience & Engineering, University of Iowa, Iowa City, IA, USA USDA National Soil Tilth Lab, Ames, IA, USA Duke 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 15 09 2009 9 18 6655 6675 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/9/6655/2009/acp-9-6655-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/6655/2009/acp-9-6655-2009.pdf

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.

 References Baez, A. P., Padilla, H., Garcia, R., Belmont, R., and Torres, M. d. C.: Measurement of indoor-outdoor carbonyls at four residential homes in Mexico City metropolitan area, Int. J. Environ. Poll., 26, 90–105, 2006. Bloss, C., Wagner, C., Bonzanini, A., Jenkin, M. E., Wirtz, K., Martin-Reviejo, M., and Pilling, M. J.: Evaluation of detailed aromatic mechanisms (MCMv3 and MCMv3.1) against environmental chamber data, Atmos. Chem. Phys., 5, 623–639, 2005a. Bloss, C., Wagner, C., Jenkin, M. E., Volkamer, R., Bloss, W. J., Lee, J. D., Heard, D. E., Wirtz, K., Martin-Reviejo, M., Rea, G., Wenger, J. C., and Pilling, M. J.: Development of a detailed chemical mechanism (MCMv3.1) for the atmospheric oxidation of aromatic hydrocarbons, Atmos. Chem. Phys, 5, 641–664, 2005b. Butler, T. M., Taraborrelli, D., Bruhl, C., Fischer, H., Harder, H., Martinez, M., Williams, J., Lawrence, M. G., and Lelieveld, J.: Improved simulation of isoprene oxidation chemistry with the ECHAM5/MESSy chemistry-climate model: lessons from the GABRIEL airborne field campaign, Atmos. Chem. Phys., 8, 4529–4546, 2008. Carr, S., Heard, D. E., and Blitz, M. A.: Comment on "Atmospheric Hydroxyl Radical Production from Electronically Excited NO<sub>2</sub> and H<sub>2</sub>O", Science, 324, 336b, doi:10.1126/science.1166669, 2009. Colman, J. J., Swanson, A. L., Meinardi, S., Barkley, C. S., Blake, D. R., and Sherwood, R.: Description of the Analysis of a Wide Range of Volatile Organic Compounds in Whole Air Samples Collected during PEM-Tropics A and B, Anal. Chem., 73, 3723–3731, 2001. crowley, J. N. and Carl, S. A.: OH Formation in the Photoexcitation of NO<sub>2</sub> beyond the Dissociation Threshold in the Presence of Water Vapor, J. Phys. Chem., 101, 4178-4184, 1997. De Foy, B., Varela, J. R., Molina, L. T., and Molina, M. J.: Rapid ventilation of the Mexico City basin and regional fate of the urban plume, Atmos. Chem. Phys., 6, 2321–2335, 2006. Di Carlo, P., Brune, W. H., Martinez, M., Harder, H., Lesher, R., Ren, X., Thornberry, T., Carroll, M. A., Young, V., Shepson, P. B., Riemer, D., Apel, E., and Campbell, C.: Missing OH Reactivity in a Forest: Evidence for Unknown Reactive Biogenic VOCs, Science, 304, 722–725, 2004. Dunlea, E. J., Herndon, S. C., Nelson, D. D., Volkamer, R. M., Lamb, B. K., Allwine, E. J., Grutter, M., Ramos-Villegas, C. R., Marquez, C., Blanco, S., Cardenas, B., Kolb, C. E., Molina, L. T., and Molina, M. J.: Technical note: Evaluation of standard ultraviolet absorption ozone monitors in a polluted urban environment, Atmos. Chem. Phys., 6, 3161–3180, 2006. Dunlea, E. J., Herndon, S. C., Nelson, D. D., Volkamer, R. M., San Martini, F., Sheehy, P. M., Zahniser, M. S., Shorter, J. H., Wormhoudt, J. C., Lamb, B. K., Allwine, E. J., Gaffney, J. S., Marley, N. A., Grutter, M., Marquez, C., Blanco, S., Cardenas, B., Retama, A., Ramos-Villegas, C. R., Kolb, C. E., Molina, L. T., and Molina, M. J.: Evaluation of nitrogen dioxide chemiluminescence monitors in a polluted urban environment, Atmos. Chem. Phys., 7, 2691–2704, 2007. Dusanter, S., Vimal, D., and Stevens, P. S.: Technical note: Measuring tropospheric OH and HO<sub>2</sub> by laser-induced fluorescence at low pressure - a comparison of calibration techniques, Atmos. Chem. Phys., 8, 321–340, 2008. Dusanter, S., Vimal, D., Stevens, P. S., Volkamer, R., and Molina, L. T.: Measurements of OH and HO<sub>2</sub> concentrations during the MCMA-2006 field campaign – Part 1: Deployment of the Indiana University laser-induced fluorescence instrument, Atmos. Chem. Phys., 9, 1665–1685, 2009. Elshorbany, Y. F., Kurtenbach, R., Wiesen, P., Lissi, E., Rubio, M., Villena, G., Gramsch, E., Rickard, A. R., Pilling, M. J., and Kleffmann, J.: Oxidation capacity of the city air of Santiago, Chile, Atmos. Chem. Phys., 9, 2257–2273, 2009. Emmerson, K. M., Carslaw, N., Carpenter, L. J., Heard, D. E., Lee, J. D., and Pilling, M. J.: Urban atmospheric chemistry during the PUMA campaign 1: Comparison of modelled OH and HO<sub>2</sub> concentrations with measurements, J. Atmos. Chem., 52, 143–164, 2005a. Emmerson, K. M., Carslaw, N., and Pilling, M. J.: Urban atmospheric chemistry during the PUMA campaign 2: Radical budgets for OH, HO<sub>2</sub> and RO<sub>2</sub>, J. Atmos. Chem., 52, 165–183, 2005b. Emmerson, K. M., Carslaw, N., Carslaw, D. C., Lee, J. D., McFiggans, G., Bloss, W. J., Gravestock, T., Heard, D. E., Hopkins, J., Ingham, T., Pilling, M. J., Smith, S. C., Jacob, M., and Monks, P. S.: Free radical modelling studies during the UK TORCH campaign in summer 2003, Atmos. Chem. Phys., 7, 167–181, 2007. Fortner, E. C., Zheng, J., Zhang, R., Berk Knighton, W., Volkamer, R. M., Sheehy, P., Molina, L., and André, M.: Measurements of Volatile Organic Compounds Using Proton Transfer Reaction – Mass Spectrometry during the MILAGRO 2006 Campaign, Atmos. Chem. Phys., 9, 467–481, 2009. George, L. A., Hard, T. M., and O'Brien, R. J.: Measurement of free radicals OH and HO<sub>2</sub> in Los Angeles smog, J. Geophys. Res., 104, 11643–11655, 1999. Heard, D. E. and Pilling, M. J.: Measurement of OH and HO<sub>2</sub> in the troposphere, Chem. Rev., 103, 5163–5198, 2003. Holland, F., Hofzumahaus, A., Schäfer, J., Kraus, A., and Pätz, H.-W.: Measurements of OH and HO<sub>2</sub> radical concentrations and photolysis frequencies during BERLIOZ, J. Geophys. Res., 108, 8246, doi:10.1029/2001JD001393, 2003. Jenkin, M. E., Saunders, S. M., and Pilling, M. J.: The tropospheric degradation of volatile organic compounds: A protocol for mechanism development, Atmos. Env., 31, 81–104, 1997. Jenkin, M. E., Saunders, S. M., Wagner, V., and Pilling, M. J.: Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part B): tropospheric degradation of aromatic volatile organic compounds, Atmos. Chem. Phys., 3, 181–193, 2003. Junkermann, W. and Burger, J. M.: A New Portable Instrument for Continuous Measurement of Formaldehyde in Ambient Air, J. Atmos. Ocean. Technol., 23, 38–45, 2006. Kanaya, Y., Cao, R., Akimoto, H., Fukuda, M., Komazaki, Y., Yokouchi, Y., Koike, M., Tanimoto, H., Takegaya, N., and Kondo, Y.: Urban photochemistry in central Tokyo: 1. Observed and modeled OH and HO$_2 $radical concentrations during the winter and summer 2004, J. Geophys. Res., 112, D21312, doi:10.1029/2007JD008670, 2007. Kleffmann, J.: Daytime Sources of Nitrous Acid (HONO) in the Atmospheric Boundary Layer, Chem. Phys. Chem., 8, 1137–1144, 2007. Kovacs, T. A., Brune, W. H., Harder, H., Martinez, M., Simpas, J. B., Frost, G. J., Williams, E., Jobson, T., Stroud, C., Young, V., Fried, A., and Wert, B.: Direct measurements of urban OH reactivity during Nashville SOS in summer 1999, J. Environ. Monit., 5, 48–74, 2003. Lewis, A. C., Carslaw, D. C., Marriott, P. J., Kinghorn, R. M., Morrison, P., Lee, A. L., Bartle, K. D., and Pilling, M. J.: Alarger pool of ozone-forming carbon compounds in urban atmospheres, Nature, 405, 778–781, 2000. Li, S., Matthews, J., and Sinha, A.: Atmospheric Hydroxyl Radical Production from Electronically Excited NO<sub>2</sub> and H<sub>2</sub>O, Science, 319, 1657–1660, 2008. Madronich, S.: Photodissociation in the atmosphere 1. Actinic flux and the effect of ground reflections and clouds, J. Geophys. Res., 92, 9740–9752, 1989. Madronich, S. and Weller, G.: Numerical integration errors in calculated tropospheric photodissociation rate coefficients, J. Atmos. Chem., 10, 289–300, 1990. Mao, J., Ren, X., Chen, S., Brune, W. H., Chen, Z., Martinez, M., Harder, H., Lefer, B., Rappengluck, B., Flynn, J., and Leuchner, M.: Atmospheric Oxidation Capacity in the Summer of Houston 2006: Comparison with Summer Measurements in Other Metropolitan Studies, Atmos. Env., doi:10.1016/j.atmosenv.2009.1001.1013, in press, 2009. Martinez, M., Harder, H., Kovacs, T. A., Simpas, J. B., Bassis, J., Lesher, R., Brune, W. H., Frost, G. J., Williams, E. J., Stroud, C. A., Jobson, B. T., Roberts, J. M., Hall, S. R., Shetter, R. E., Wert, B., Fried, A., Alicke, B., Stutz, J., Young, V. L., White, A. B., and Zamora, R. J.: OH and HO<sub>2</sub> concentrations, sources, and loss rates during the Southern Oxidants Study in Nashville, Tennesse, summer 1999, J. Geophys. Res., 108, 4617, doi:10.1029/2003JD003551, 2003. Merten, A.: New design of Longpath-DOAS instruments based on fibre optics and applications in the study of the urban atmosphere, Thesis, Heidelberg, Univ., Germany, 2008. Monks, P. S., Rickard, A. R., and Stacey, L. H.: Attenuation of spectral actinic flux and photolysis frequencies at the surface through homogenous cloud fields, J. Geophys. Res., 109, D17206, doi:10.1029/2003JD004076, 2004. Platt, U., Alicke, B., Dubois, R., Geyer, A., Hofzumahaus, A., Holland, F., Martinez, M., Mihelcic, D., Klupfel, T., Lohrmann, B., Patz, W., Perner, D., Rohrer, F., Schafer, J., and Stutz, J.: Free radicals and fast photochemistry during BERLIOZ, J. Atmos. Chem., 42, 359–394, 2002. Ren, X., Harder, H., Martinez, M., Lesher, R. L., Oliger, A., Simpas, J. B., Brune, W. H., Schwab, J. J., Demerjian, K. L., He, Y., Zhou, X., and Gao, H.: OH and HO<sub>2</sub> Chemistry in the urban atmosphere of New York City, Atmos. Environ., 37, 3639–3651, 2003. Sander, S. P., Friedl, R. R., Golden, D. M., Kurylo, M. J., Moortgat, G. K., Wine, P. H., Ravishankara, A. R., Kolb, C. E., Molina, M. J., Finlayson-Pitts, B. J., Huie, R. E., and Orkin, V. L.: Chemical kinetics and photochemical data for use in atmospheric studies, Evaluation number 15, JPL Publication 06-2, NASA Jet Propulsion Laboratory, Pasadena, California, USA 2006. Saunders, S. M., Jenkin, M. E., Derwent, R. G., and Pilling, M. J.: Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part A): Tropospheric degradation of non-aromatic volatile organic compounds, Atmos. Chem. Phys., 3, 161–180, 2003. Sheehy, P., Volkamer, R., Molina, L. T., and Molina, M. J.: Oxidative capacity of the Mexico City atmosphere - Part 2: A RO<sub>x</sub> radical cycling perspective, Atmos. Chem. Phys. Discuss., 8, 5359–5412, 2008. Shirley, T. R., Brune, W. H., Ren, X., Mao, J., Lesher, R., Cardenas, B., Volkamer, R., Molina, L. T., Molina, L. T., Lamb, B., Velasco, E., Jobson, T., and Alexander, M.: Atmospheric oxidation in the Mexico City Metropolitan Area (MCMA) during April 2003, Atmos. Chem. Phys., 6, 2753–2765, 2006. Sillman, S.: Tropospheric ozone: The debate over control strategies, Annu. Rev. Energy Environ., 18, 31–56, 1993. Sinha, V., Crowley, J. N., and Lelieveld, J.: The Comparative Reactivity Method – a new tool to measure total OH Reactivity in ambient air, Atmos. Chem. Phys., 8, 2213-2227, 2008. Stockwell, W. R., Kirchner, F., and Kuhn, M.: A new mechanism for regional atmospheric chemistry modeling, J. Geophys. Res., 102, 25847–25879, 1997. Velasco, E., Lamb, B., Westberg, H., Allwine, E., Sosa, G., Ariaga-Colina, J. L., Jobson, B. T., Alexander, M. L., Prazeller, P., Knighton, W. B., Rogers, T. M., Grutter, M., Herndon, S. C., Kolb, C. E., Zavala, M., Foy, B. d., Volkamer, R., Molina, L. T., and Molina, M. J.: Distribution, magnitudes, reactivities, ratios and diurnal patterns of volatile organic compounds in the Valley of Mexico during the MCMA 2002 & 2003 field campaigns, Atmos. Chem. Phys., 7, 329–353, 2007. Volkamer, R., Jimenez, J. L., San Martini, F., Dzepina, K., Zhang, Q., Salcedo, D., Molina, L. T., Worsnop, D. R., and Molina, M. J.: Secondary organic aerosol formation from anthropogenic air pollution: Rapid and higher than expected, J. Geophys. Res., 33, doi:10.1029/2006GL026899, L17811, 2006. Volkamer, R., Martini, F. S., Molina, L. T., Salcedo, D., Jiminez, J. L., and Molina, M. J.: A missing sink for gas-phase glyoxal in Mexico City: Formation of secondary organic aerosol, Geophys. Res. Lett., 34, L19807, doi:10.1029/2007GL030752, 2007a. Volkamer, R., Sheehy, P. M., Molina, L. T., and Molina, M. J.: Oxidative capacity of the Mexico City atmosphere - Part 1: A radical source perspective, Atmos. Chem. Phys. Discuss., 7, 5365–5412, 2007b. Volkamer, R., Ziemann, P. J., and Molina, M. J.: Secondary Organic Aerosol Formation from Acetylene (C2H2): seed effect on SOA yields due to organic photochemistry in the aerosol aqueous phase, Atmos. Chem. Phys., 9, 1907–1928, 2009. Wennberg, P. O. and Dabdub, D.: Rethinking Ozone Production, Science, 319, 1624–1625, 2008. Yoshino, A., Sadanaga, Y., Watanabe, K., Kato, S., Miyakawa, Y., Matsumoto, J., and Kajii, Y.: Measurement of total OH reactivity by laser-induced pump and probe technique – comprehensive observations in the urban atmosphere of Tokyo, Atmos. Env., 40, 7869–7881, 2006. Zheng, J., Zhang, R., Fortner, E., Volkamer, R., Molina, L., Aiken, A. C., Jimenez, J. L., Gaeggeler, K., Dommen, J., Dusanter, S., Stevens, P. S., and Tie, X.: Measurements of HNO<sub>3</sub> and N<sub>2</sub>O$_5$ using ion drift-chemical ionization mass spectrometry during the MILAGRO/MCMA-2006 campaign, Atmos. Chem. Phys., 8, 6823–6838, 2008.