References

ACP

Atmospheric Chemistry and Physics

ACP

1680-7324

Copernicus GmbH

Göttingen, Germany

10.5194/acp-12-1541-2012

Observation and modelling of OH and HO2 concentrations in the Pearl River Delta 2006: a missing OH source in a VOC rich atmosphere

K. D.

¹ ² Rohrer

² Holland

² Fuchs

² Bohn

² Brauers

² Chang

C. C.

³ Häseler

² Hu

¹ Kita

⁴ Kondo

⁵ Li

¹ ² Lou

S. R.

² ⁶ ⁷ Nehr

² Shao

¹ Zeng

L. M.

¹ Wahner

² Zhang

Y. H.

¹ Hofzumahaus

College of Environmental Sciences and Engineering, Peking University, Beijing, China

Institut für Energie und Klimaforschung: Troposphäre, Forschungszentrum Jülich, Jülich, Germany

Research Center for Environmental Changes, Academic Sinica, Taipei, China

Faculty of Science, Ibaraki University, Ibaraki, Japan

University of Tokyo, Research Center for Advanced Science and Technology, Tokyo, Japan

School of Environmental Science and Technology, Shanghai Jiao Tong University, Shanghai, China

now at: Shanghai Academy Of Environmental Sciences, Shanghai, China

09 02 2012

12 3 1541 1569

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Ambient OH and HO2 concentrations were measured by laser induced fluorescence (LIF) during the PRIDE-PRD2006 (Program of Regional Integrated Experiments of Air Quality over the Pearl River Delta, 2006) campaign at a rural site downwind of the megacity of Guangzhou in Southern China. The observed OH concentrations reached daily peak values of (15–26) × 106 cm−3 which are among the highest values so far reported for urban and suburban areas. The observed OH shows a consistent high correlation with j(O1D) over a broad range of NOx conditions. The correlation cannot be reproduced by model simulations, indicating that OH stabilizing processes are missing in current models. The observed OH exhibited a weak dependence on NOx in contrast to model predictions. While modelled and measured OH agree well at NO mixing ratios above 1 ppb, a continuously increasing underprediction of the observed OH is found towards lower NO concentrations, reaching a factor of 8 at 0.02 ppb NO. A dependence of the modelled-to-measured OH ratio on isoprene cannot be concluded from the PRD data. However, the magnitude of the ratio fits into the isoprene dependent trend that was reported from other campaigns in forested regions. Hofzumahaus et al. (2009) proposed an unknown OH recycling process without NO, in order to explain the high OH levels at PRD in the presence of high VOC reactivity and low NO. Taking a recently discovered interference in the LIF measurement of HO2 into account, the need for an additional HO2 → OH recycling process persists, but the required source strength may be up to 20% larger than previously determined. Recently postulated isoprene mechanisms by Lelieveld et al. (2008) and Peeters and Müller (2010) lead to significant enhancements of OH expected for PRD, but an underprediction of the observed OH by a factor of two remains at low NO (0.1–0.2 ppb). If the photolysis of hydroperoxy aldehydes from isoprene is as efficient as proposed by Peeters and Müller (2010), the corresponding OH formation at PRD would be more important than the primary OH production from ozone and HONO. While the new isoprene mechanisms need to be confirmed by laboratory experiments, there is probably need for other, so far unidentified chemical processes to explain entirely the high OH levels observed in Southern China.

References 1

Andrés-Hernández, M D., Stone, D., Brookes, D M., Commane, R., Reeves, C E., Huntrieser, H., Heard, D E., Monks, P S., Burrows, J P., Schlager, H., Kartal, D., Evans, M J., Floquet, C. F A., Ingham, T., Methven, J., and Parker, A E.: Peroxy radical partitioning during the AMMA radical intercomparison exercise, Atmos. Chem. Phys., 10, 10621–10638, http://dx.doi.org/10.5194/acp-10-10621-2010doi:10.5194/acp-10-10621-2010, 2010.

Archibald, A T., Cooke, M C., Utembe, S R., Shallcross, D E., Derwent, R G., and Jenkin, M E.: Impacts of mechanistic changes on HOx formation and recycling in the oxidation of isoprene, Atmos. Chem. Phys., 10, 8097–8118, http://dx.doi.org/10.5194/acp-10-8097-2010doi:10.5194/acp-10-8097-2010, 2010.

Atkinson, R.: Atmospheric reactions of alkoxy and β-hydroxyalkoxy radicals, Int. J. Chem. Kin., 29, 99–111, 1997.

Bedjanian, Y., Lelievre, S., and Le Bras, G.: Experimental study of the interaction of HO2 radicals with soot surface, Phys. Chem. Chem. Phys., 7, 334–341, 2005.

Berresheim, H., Plass-Dülmer, C., Elste, T., Mihalopoulos, N., and Rohrer, F.: OH in the coastal boundary layer of Crete during MINOS: Measurements and relationship with ozone photolysis, Atmos. Chem. Phys., 3, 639–649, http://dx.doi.org/10.5194/acp-3-639-2003doi:10.5194/acp-3-639-2003, 2003.

Bloss, W J., Lee, J D., Johnson, G P., Sommariva, R., Heard, D E., Saiz-Lopez, A., Plane, J. M C., McFiggans, G., Coe, H., Flynn, M., Williams, P., Rickard, A R., and Fleming, Z L.: Impact of halogen monoxide chemistry upon boundary layer OH and HO2 concentrations at a coastal site, Geophys. Res. Lett, 32, L06814, http://dx.doi.org/10.1029/2004GL022084doi:10.1029/2004GL022084, 2005.

Bohn, B., Corlett, G. K., Gillmann, M., Sanghavi, S., Stange, G., Tensing, E., Vrekoussis, M., Bloss, W. J., Clapp, L. J., Kortner, M., Dorn, H.-P., Monks, P. S., Platt, U., Plass-Dülmer, C., Mihalopoulos, N., Heard, D. E., Clemitshaw, K. C., Meixner, F. X., Prevot, A. S. H., and Schmitt, R.: Photolysis frequency measurement techniques: results of a comparison within the ACCENT project, Atmos. Chem. Phys., 8, 5373–5391, http://dx.doi.org/10.5194/acp-8-5373-2008doi:10.5194/acp-8-5373-2008, 2008.

Brasseur, G P., Prinn, R G., and Pszenny, A P. (Eds.): Atmospheric Chemistry in a Changing World, The IGBP Series, Springer, Berlin, 2003.

Brauers, T., Hausmann, M., Bister, A., Kraus, A., and Dorn, H P.: OH radicals in the boundary layer of the Atlantic Ocean 1. Measurements by long-path laser absorption spectroscopy, J. Geophys. Res., 106, 7399–7414, 2001.

Butler, T M., Taraborrelli, D., Brühl, 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, http://dx.doi.org/10.5194/acp-8-4529-2008doi:10.5194/acp-8-4529-2008, 2008.

Carslaw, N., Creasey, D J., Heard, D E., Lewis, A C., McQuaid, J B., Pilling, M J., Monks, P S., Bandy, B J., and Penkett, S A.: Modeling OH, HO2, and RO2 radicals in the marine boundary layer – 1. Model construction and comparison with field measurements, J. Geophys. Res., 104, 30241–30255, 1999.

Carslaw, N., Creasey, D., Heard, D., Jacobs, P., Lee, J., Lewis, A., Bauguitte, S., Penkett, S., Monks, P., and Salisbury, G.: Eastern Atlantic Spring Experiment 1997 (EASE97) 2. Comparisons of model concentrations of OH, HO2, and RO2 with measurements, J. Geophys. Res., 107, 4190, http://dx.doi.org/10.1029/2001JD001568doi:10.1029/2001JD001568, 2002.

Chan, C K. and Yao, X.: Air pollution in mega cities in China, Atmos. Environ., 42, 1–42, 2008.

Crawford, J., Davis, D., Olson, J., Chen, G., Liu, S., Gregory, G., Barrick, J., Sachse, G., Sandholm, S., Heikes, B., Singh, H., and Blake, D.: Assessment of upper tropospheric HOx sources over the tropical Pacific based on NASA GTE/PEM data: Net effect on HOx and other photochemical parameters, J. Geophys. Res., 104, 16255–16273, 1999.

Creasey, D J., Heard, D E., and Lee, J D.: Eastern Atlantic Spring Experiment 1997 (EASE97) 1. Measurements of OH and HO2 concentrations at Mace Head, Ireland, J. Geophys. Res., 107, D104091, http://dx.doi.org/10.1029/2001JD000892doi:10.1029/2001JD000892, 2002.

Crosley, D R.: The measurement of OH and HO2 in the atmosphere, J. Atmos. Sci., 52, 3299–3314, 1995.

Crounse, J D., Paulot, F., Kjaergaard, H G., and Wennberg, P O.: Peroxy radical isomerization in the oxidation of isoprene, Phys. Chem. Chem. Phys., 13, 13607–13613, http://dx.doi.org/10.1039/c1cp21330jdoi:10.1039/c1cp21330j, 2011.

Dillon, T J. and Crowley, J N.: Direct detection of OH formation in the reactions of HO2 with CH3C(O)O2 and other substituted peroxy radicals, Atmos. Chem. Phys., 8, 4877–4889, http://dx.doi.org/10.5194/acp-8-4877-2008doi:10.5194/acp-8-4877-2008, 2008.

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., and Holder, H.: Measurements of OH and HO2 concentrations during the MCMA-2006 field campaign – Part 2: Model comparison and radical budget, Atmos. Chem. Phys., 9, 6655–6675, http://dx.doi.org/10.5194/acp-9-6655-2009doi:10.5194/acp-9-6655-2009, 2009.

Ehhalt, D H.: Photooxidation of trace gases in the troposphere, Phys. Chem. Chem. Phys., 1, 5401–5408, 1999.

Ehhalt, D H. and Rohrer, F.: Dependence of the OH concentration on solar UV, J. Geophys. Res., 105, 3565–3571, 2000.

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 HO2 concentrations with measurements, J. Atmos. Chem., 52, 143–164, 2005.

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, http://dx.doi.org/10.5194/acp-7-167-2007doi:10.5194/acp-7-167-2007, 2007.

Finlayson-Pitts, B J. and Pitts Jr., J N.: Chemistry of the upper and lower atmosphere: Theory, experiments and applications, Academic Press, San Diego, 2000.

Fuchs, H., Bohn, B., Hofzumahaus, A., Holland, F., Lu, K D., Nehr, S., Rohrer, F., and Wahner, A.: Detection of HO2 by laser-induced fluorescence: calibration and interferences from RO2 radicals, Atmos. Meas. Tech., 4, 1209–1225, http://dx.doi.org/10.5194/amt-4-1209-2011doi:10.5194/amt-4-1209-2011, 2011.

Garland, R. M., Yang, H., Schmid, O., Rose, D., Nowak, A., Achtert, P., Wiedensohler, A., Takegawa, N., Kita, K., Miyazaki, Y., Kondo, Y., Hu, M., Shao, M., Zeng, L. M., Zhang, Y. H., Andreae, M. O., and Pöschl, U.: Aerosol optical properties in a rural environment near the mega-city Guangzhou, China: implications for regional air pollution, radiative forcing and remote sensing, Atmos. Chem. Phys., 8, 5161–5186, http://dx.doi.org/10.5194/acp-8-5161-2008doi:10.5194/acp-8-5161-2008, 2008.

Geiger, H., Barnes, I., Bejan, I., Benter, T., and Spittler, M.: The tropospheric degradation of isoprene: an updated module for the regional atmospheric chemistry mechanism, Atmos. Environ., 37, 1503–1519, 2003.

George, L A., Hard, T M., and O'Brien, R J.: Measurement of free radicals OH and HO2 in Los Angeles smog, J. Geophys. Res., 104, 11643–11655, 1999.

Hallquist, M., Wenger, J. C., Baltensperger, U., Rudich, Y., Simpson, D., Claeys, M., Dommen, J., Donahue, N. M., George, C., Goldstein, A. H., Hamilton, J. F., Herrmann, H., Hoffmann, T., Iinuma, Y., Jang, M., Jenkin, M. E., Jimenez, J. L., Kiendler-Scharr, A., Maenhaut, W., McFiggans, G., Mentel, Th. F., Monod, A., Prévôt, A. S. H., Seinfeld, J. H., Surratt, J. D., Szmigielski, R., and Wildt, J.: The formation, properties and impact of secondary organic aerosol: current and emerging issues, Atmos. Chem. Phys., 9, 5155–5236, http://dx.doi.org/10.5194/acp-9-5155-2009doi:10.5194/acp-9-5155-2009, 2009.

Hanke, M., Uecker, J., Reiner, T., and Arnold, F.: Atmospheric peroxy radicals: ROXMAS, a new mass-spectrometric methodology for speciated measurements of HO2 and $§igma$RO2 and first results, Int. J. Mass Spectrom., 213, 91–99, 2002.

Harrison, R M., Yin, J., Tilling, R M., Cai, X., Seakins, P W., Hopkins, J R., Lansley, D L., Lewis, A C., Hunter, M C., Heard, D E., Carpenter, L J., Creasey, D J., Lee, J D., Pilling, M J., Carslaw, N., Emmerson, K M., Redington, A., Derwent, R G., Ryall, D., Mills, G., and Penkett, S A.: Measurement and modelling of air pollution and atmospheric chemistry in the U.K. West Midlands conurbation: Overview of the PUMA Consortium project, Sci. Total. Environ., 360, 5–25, 2006.

Hasson, A S., Tyndall, G S., and Orlando, J J.: A product yield study of the reaction of HO2 radicals with ethyl peroxy (C2H$_5$O2), acetyl peroxy (CH3C(O)O2), and acetonyl peroxy (CH3C(O)CH2O2) radicals, J. Phys. Chem. A, 108, 5979–5989, 2004.

Heard, D E. and Pilling, M J.: Measurement of OH and HO2 in the Troposphere, Chem. Rev., 103, 5163–5198, 2003.

Hofzumahaus, A., Aschmutat, U., Heß ling, M., Holland, F., and Ehhalt, D H.: The measurement of tropospheric OH radicals by laser-induced fluorescence spectroscopy during the POPCORN field campaign, Geophys. Res. Lett., 23, 2541–2544, 1996.

Hofzumahaus, A., Aschmutat, U., Brandenburger, U., Brauers, T., Dorn, H.-P., Hausmann, M., Hessling, M., Holland, F., Plass-Dülmer, C., and Ehhalt, D H.: Intercomparison of tropospheric OH measurements by different laser techniques during the POPCORN Campaign 1994, J. Atmos. Chem., 31, 227–246, 1998.

Hofzumahaus, A., Rohrer, F., Lu, K., Bohn, B., Brauers, T., Chang, C C., Fuchs, H., Holland, F., Kita, K., Kondo, Y., Li, X., Lou, S., Shao, M., Zeng, L., Wahner, A., and Zhang, Y.: Amplified Trace Gas Removal in the Troposphere, Science, 324, 1702–1704, 2009.

Holland, F., Heß ling, M., and Hofzumahaus, A.: In situ measurement of tropospheric OH radicals by laser-induced fluorescence – A description of the KFA instrument, J. Atmos. Sci., 52, 3393–3401, 1995.

Holland, F., Aschmutat, U., Heß ling, M., Hofzumahaus, A., and Ehhalt, D H.: Highly time resolved measurements of OH during POPCORN using laser-induced fluorescence spectroscopy, J. Atmos. Chem., 31, 205–225, 1998.

Holland, F., Hofzumahaus, A., Schäfer, J., Kraus, A., and Pätz, H.-W.: Measurements of OH and HO2 radical concentrations and photolysis frequencies during BERLIOZ, J. Geophys. Res., 108, 8246, http://dx.doi.org/10.1029/2001JD001393doi:10.1029/2001JD001393, 2003.

Hornbrook, R. S., Crawford, J. H., Edwards, G. D., Goyea, O., Mauldin III, R. L., Olson, J. S., and Cantrell, C. A.: Measurements of tropospheric HO2 and RO2 by oxygen dilution modulation and chemical ionization mass spectrometry, Atmos. Meas. Tech., 4, 735–756, http://dx.doi.org/10.5194/amt-4-735-2011doi:10.5194/amt-4-735-2011, 2011.

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, http://dx.doi.org/10.5194/acp-3-181-2003doi:10.5194/acp-3-181-2003, 2003.

Jenkin, M E., Hurley, M D., and Wallington, T J.: Investigation of the radical product channel of the CH3C(O)O2+HO2 reaction in the gas phase, Phys. Chem. Chem. Phys., 9, 3149–3162, 2007.

Jenkin, M E., Hurley, M D., and Wallington, T J.: Investigation of the radical product channel of the CH3OCH2O2 + HO2 reaction in the gas phase, J. Phys. Chem. A, 114, 408�–416, 2010.

Kanakidou, M., Seinfeld, J. H., Pandis, S. N., Barnes, I., Dentener, F. J., Facchini, M. C., Van Dingenen, R., Ervens, B., Nenes, A., Nielsen, C. J., Swietlicki, E., Putaud, J. P., Balkanski, Y., Fuzzi, S., Horth, J., Moortgat, G. K., Winterhalter, R., Myhre, C. E. L., Tsigaridis, K., Vignati, E., Stephanou, E. G., and Wilson, J.: Organic aerosol and global climate modelling: a review, Atmos. Chem. Phys., 5, 1053–1123, http://dx.doi.org/10.5194/acp-5-1053-2005doi:10.5194/acp-5-1053-2005, 2005.

Kanaya, Y., Sadanaga, Y., Matsumoto, J., Sharma, U K., Hirokawa, J., Kajii, Y., and Akimoto, H.: Daytime HO2 concentrations at Oki Island, Japan, in summer 1998: Comparison between measurement and theory, J. Geophys. Res., 105, 24205–24222, 2000.

Kanaya, Y., Sadanaga, Y., Hirokawa, J., Kajii, Y., and Akimoto, H.: Development of a ground-based LIF instrument for measuring HO$\rm_x$ radicals: Instrumentation and calibrations, J. Atmos. Chem., 38, 73–110, 2001.

Kanaya, Y., Cao, R., Kato, S., Miyakawa, Y., Kajii, Y., Tanimoto, H., Yokouchi, Y., Mochida, M., Kawamura, K., and Akimoto, H.: Chemistry of OH and HO2 radicals observed at Rishiri Island, Japan, in September 2003: Missing daytime sink of HO2 and positive nighttime correlations with monoterpenes, J. Geophys. Res., 112, D11308, http://dx.doi.org/10.1029/2006JD007987doi:10.1029/2006JD007987, 2007a.

Kanaya, Y., Cao, R Q., Akimoto, H., Fukuda, M., Komazaki, Y., Yokouchi, Y., Koike, M., Tanimoto, H., Takegawa, N., and Kondo, Y.: Urban photochemistry in central Tokyo: 1. Observed and modeled OH and HO2 radical concentrations during the winter and summer of 2004, J. Geophys. Res., 112, D21312, http://dx.doi.org/10.1029/2007JD008670doi:10.1029/2007JD008670, 2007b.

Karl, M., Dorn, H.-P., Holland, F., Koppmann, R., Poppe, D., Rupp, L., Schaub, A., and Wahner, A.: Product study of the reaction of OH radicals with isoprene in the atmosphere simulation chamber SAPHIR, J. Atmos. Chem., 55, 167–187, 2006.

Kleffmann, J., Gavriloaiei, T., Hofzumahaus, A., Holland, F., Koppmann, R., Rupp, L., Schlosser, E., Siese, M., and Wahner, A.: Daytime formation of nitrous acid: A major source of OH radicals in a forest, Geophys. Res. Lett., 32, L05818, http://dx.doi.org/10.1029/2005GL022524doi:10.1029/2005GL022524, 2005.

Kolb, C. E., Cox, R. A., Abbatt, J. P. D., Ammann, M., Davis, E. J., Donaldson, D. J., Garrett, B. C., George, C., Griffiths, P. T., Hanson, D. R., Kulmala, M., McFiggans, G., Pöschl, U., Riipinen, I., Rossi, M. J., Rudich, Y., Wagner, P. E., Winkler, P. M., Worsnop, D. R., and O' Dowd, C. D.: An overview of current issues in the uptake of atmospheric trace gases by aerosols and clouds, Atmos. Chem. Phys., 10, 10561–10605, http://dx.doi.org/10.5194/acp-10-10561-2010doi:10.5194/acp-10-10561-2010, 2010.

Kubistin, D., Harder, H., Martinez, M., Rudolf, M., Sander, R., Bozem, H., Eerdekens, G., Fischer, H., Gurk, C., Klüpfel, T., Königstedt, R., Parchatka, U., Schiller, C L., Stickler, A., Taraborrelli, D., Williams, J., and Lelieveld, J.: Hydroxyl radicals in the tropical troposphere over the Suriname rainforest: comparison of measurements with the box model MECCA, Atmos. Chem. Phys., 10, 9705–9728, http://dx.doi.org/10.5194/acp-10-9705-2010doi:10.5194/acp-10-9705-2010, 2010.

Lelieveld, J., Butler, T M., Crowley, J N., Dillon, T J., Fischer, H., Ganzeveld, L., Harder, H., Lawrence, M G., Martinez, M., Taraborelli, D., and Williams, J.: Atmospheric oxidation capacity sustained by a tropical forest, Nature, 452, 737–740, 2008.

Lewis, A. C., Hopkins, J. R., Carpenter, L. J., Stanton, J., Read, K. A., and Pilling, M. J.: Sources and sinks of acetone, methanol, and acetaldehyde in North Atlantic marine air, Atmos. Chem. Phys., 5, 1963–1974, http://dx.doi.org/10.5194/acp-5-1963-2005doi:10.5194/acp-5-1963-2005, 2005.

Li, S P., Matthews, J., and Sinha, A.: Atmospheric hydroxyl radical production from electronically excited NO2 and H2O, Science, 319, 1657–1660, 2008.

Li, X., Brauers, T., Hofzumahaus, A., Lu, K., Li, Y. P., Shao, M., Wagner, T., and Wahner, A.: MAX-DOAS measurements of NO2, HCHO and CHOCHO at a rural site in Southern China, Atmos. Chem. Phys. Discuss., 12, 3983–4029, http://dx.doi.org/10.5194/acpd-12-3983-2012doi:10.5194/acpd-12-3983-2012, 2012.

Li, X., Brauers, T., Häseler, R., Bohn, B., Hofzumahaus, A., Holland, F., Lu, K. D., Rohrer, F., Hu, M., Zeng, L. M., Zhang, Y. H., Garland, R., Su, H., Nowak, A., Takegawa, N., Shao, M., and Wahner, A.: Exploring the atmospheric chemistry of nitrous acid (HONO) at a rural site in Southern China, Atmos. Chem. Phys. Discuss., 11, 27591–27635, http://dx.doi.org/10.5194/acpd-11-27591-2011doi:10.5194/acpd-11-27591-2011, 2011.

Lou, S., Holland, F., Rohrer, F., Lu, K., Bohn, B., Brauers, T., Chang, C., Fuchs, H., Häseler, R., Kita, K., Kondo, Y., Li, X., Shao, M., Zeng, L., Wahner, A., Zhang, Y., Wang, W., and Hofzumahaus, A.: Atmospheric OH reactivities in the Pearl River Delta – China in summer 2006: measurement and model results, Atmos. Chem. Phys., 10, 11243–11260, http://dx.doi.org/10.5194/acp-10-11243-2010doi:10.5194/acp-10-11243-2010, 2010.

Lu, K D., Zhang, Y H., Su, H., Shao, M., Zeng, L M., Zhong, L J., Xiang, Y R., Chang, C C., Chou, C. K C., and Wahner, A.: Regional ozone pollution and key controlling factors of photochemical ozone production in Pearl River Delta during summer time, Sci. China, Ser. B, 53, 651–663, 2010.

Lu, K. D., Rohrer, F., Hofzumahaus, A., et al.: Nighttime HOx chemistry in the Pearl River Delta and Beijing in summer 2006, Atmos. Chem. Phys. Discuss., in preparation, 2012.

Mao, J., Ren, X., Chen, S., Brune, W H., Chen, Z., Martinez, M., Harder, H., Lefer, B., Rappenglück, B., Flynn, J., and Leuchner, M.: Atmospheric oxidation capacity in the summer of Houston 2006: Comparison with summer measurements in other metropolitan studies, Atmos. Environ., 44, 4107–4115, http://dx.doi.org/10.1016/j.atmosenv.2009.01.013doi:10.1016/j.atmosenv.2009.01.013, 2010.

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 HO2 concentrations, sources, and loss rates during the Southern Oxidants Study in Nashville, Tennessee, summer 1999, J. Geophys. Res., 108, 4617, http://dx.doi.org/10.1029/2003JD003551doi:10.1029/2003JD003551, 2003.

McKeen, S A., Mount, G., Eisele, F., Williams, E., Harder, J., Goldan, P., Kuster, W., Liu, S C., Baumann, K., Tanner, D., Fried, A., Sewell, S., Cantrell, C., and Shetter, R.: Photochemical modeling of hydroxyl and its relationship to other species during the Tropospheric OH Photochemistry Experiment, J. Geophys. Res., 102, 6467–6493, 1997.

Mihelcic, D., Holland, F., Hofzumahaus, A., Hoppe, L., Konrad, S., Müsgen, P., Pätz, H.-W., Schäfer, H.-J., Schmitz, T., Volz-Thomas, A., Bächmann, K., Schlomski, S., Platt, U., Geyer, A., Alicke, B., Perner, D., Klüpfel, T., and Moortgat, G K.: Comparison of measurements and model calculations of OH, HO2, and $§igma$RO2 and the local ozone production during the BERLIOZ campaign, J. Geophys. Res., 108, 8254, http://dx.doi.org/10.1029/2001JD001014doi:10.1029/2001JD001014, 2003.

Monks, P S., Granier, C., Fuzzie, S., Stohl, A., Williams, M., Akimoto, H., Ammani, M., Baklanov, A., Baltensperger, U., Bey, I., Blake, N., Blake, R., Carslaw, K., Cooper, O., Dentener, F., Fowler, D., Fragkou, E., Frost, G., Generoso, S., Ginoux, P., Grewe, V., abd H C Hansson, A G., Henne, S., Hjorth, J., Hofzumahaus, A., Huntrieser, H., Isaksen, I. S A., Jenkin, M E., Kaiser, J., Kanakidou, M., Klimont, Z., Kulmala, M., Laj, P., Lawrence, M., Lee, J., Liousse, C., Maione, M., McFiggans, G., Metzger, A., Mieville, A., Moussiopoulos, N., Orlando, J., O'Dowd, C., Palmer, P., Parrish, D., Petzold, A., Platt, U., Pöschl, U., Prévôt, A. S H., Reeves, C E., Reimann, S., Rudich, Y., Sellegri, K., Steinbrecher, R., Simpson, D., ten Brink, H., Theloke, J., van der Werf, G R., Vautard, R., Vestreng, V., Vlachokostas, C., and vonGlasow, R.: Atmospheric Composition Change – Global and Regional Air Quality, Atmos. Environ., 43, 5268–5350, 2009.

Nehr, S., Bohn, B., Fuchs, H., and Hofzumahaus, A.: HO2 formation from the OH + benzene reaction in the presence of O2, Phys. Chem. Chem. Phys., 13, 10699–10708, http://dx.doi.org/10.1039/C1CP20334Gdoi:10.1039/C1CP20334G, 2011.

Paulot, F., Crounse, J D., Kjaergaard, H G., Kroll, J H., Seinfeld, J H., and Wennberg, P O.: Isoprene photooxidation: new insights into the production of acids and organic nitrates, Atmos. Chem. Phys., 9, 1479–1501, http://dx.doi.org/10.5194/acp-9-1479-2009doi:10.5194/acp-9-1479-2009, 2009.

Peeters, J. and Müller, J.-F.: HOx radical regeneration in isoprene oxidation via peroxy radical isomerisations. II: experimental evidence and global impact, Phys. Chem. Chem. Phys., 12, 14227–14235, http://dx.doi.org/10.1039/c0cp00811gdoi:10.1039/c0cp00811g, 2010.

Peeters, J., Nguyen, T L., and Vereecken, L.: HOx radical regeneration in the oxidation of isoprene, Phys. Chem. Chem. Phys., 11, 5935–5939, 2009.

Platt, U., Alicke, B., Dubois, R., Geyer, A., Hofzumahaus, A., Holland, F., Martinez, M., Mihelcic, D., Klüpfel, T., Lohrmann, B., Pätz, W., Perner, D., Rohrer, F., Schäfer, J., and Stutz, J.: Free radicals and fast photochemistry during BERLIOZ, J. Atmos. Chem., 42, 359–394, 2002.

Poppe, D., Wallasch, M., and Zimmermann, J.: The Dependence of the Concentration of OH on its Precursors under Moderately Polluted Conditions: A Model Study, J. Atmos. Chem., 16, 61–78, 1993.

Poppe, D., Zimmermann, J., and Dorn, H P.: Field Data and Model-Calculations for the Hydroxyl Radical, J. Atmos. Sci., 52, 3402–3407, 1995.

Pöschl, U., von Kuhlmann, R., Poisson, N., and Crutzen, P J.: Development and intercomparison of condensed isoprene oxidation mechanisms for global atmospheric modeling, J. Atmos. Chem., 37, 29–52, 2000.

Pugh, T. A M., MacKenzie, A R., Hewitt, C N., Langford, B., Edwards, P M., Furneaux, K L., Heard, D E., Hopkins, J R., Jones, C E., Karunaharan, A., Lee, J., Mills, G., Misztal, P., Moller, S., Monks, P S., and Whalley, L K.: Simulating atmospheric composition over a South-East Asian tropical rainforest: performance of a chemistry box model, Atmos. Chem. Phys., 10, 279–298, http://dx.doi.org/10.5194/acp-10-279-2010doi:10.5194/acp-10-279-2010, 2010.

Read, K A., Mahajan, A S., Carpenter, L J., Evans, M J., Faria, B. V E., Heard, D E., Hopkins, J R., Lee, J D., Moller, S J., Lewis, A C., Mendes, L., McQuaid, J B., Oetjen, H., Saiz-Lopez, A., Pilling, M J., and Plane, J. M C.: Extensive halogen-mediated ozone destruction over the tropical Atlantic Ocean, Nature, 453, 1232–1235, 2008.

Ren, X., Harder, H., Martinez, M., Lesher, R L., Oliger, A., Shirley, T., Adams, J., Simpas, J B., and Brune, W H.: HOx concentrations and OH reactivity observations in New York City during PMTACS-NY2001, Atmos. Environ., 37, 3627–3637, 2003.

Ren, X., Harder, H., Martinez, M., Faloona, I C., Tan, D., Lesher, R L., Di Carlo, P., Simpas, J B., and Brune, W H.: Interference Testing for Atmospheric HOx Measurements by Laser-induced Fluorescence, J. Atmos. Chem., 47, 169–190, 2004.

Ren, X., Olson, J R., Crawford, J H., Brune, W H., Mao, J., Long, R B., Chen, G., Avery, M A., Sachse, G W., Barrick, J D., Diskin, G S., Huey, L G., Fried, A., Cohen, R C., Heikes, B., Wennberg, P., Singh, H B., Richard, D. R B., and Shetter, E.: HOx Chemistry during INTEX-A 2004: Observation, Model Calculations and comparison with previous studies, J. Geophys. Res., 113, D05310, http://dx.doi.org/10.1029/2007JD009166doi:10.1029/2007JD009166, 2008.

Ren, X R., Edwards, G D., Cantrell, C A., Lesher, R L., Metcalf, A R., Shirley, T., and Brune, W H.: Intercomparison of peroxy radical measurements at a rural site using laser-induced fluorescence and Peroxy Radical Chemical Ionization Mass Spectrometer (PerCIMS) techniques, J. Geophys. Res., 108, D194605, http://dx.doi.org/10.1029/2003JD003644doi:10.1029/2003JD003644, 2003.

Rohrer, F. and Berresheim, H.: Strong correlation between levels of tropospheric hydroxyl radicals and solar ultraviolet radiation, Nature, 442, 184–187, 2006.

Rose, D., Nowak, A., Achtert, P., Wiedensohler, A., Hu, M., Shao, M., Zhang, Y., Andreae, M. O., and Pöschl, U.: Cloud condensation nuclei in polluted air and biomass burning smoke near the mega-city Guangzhou, China – Part 1: Size-resolved measurements and implications for the modeling of aerosol particle hygroscopicity and CCN activity, Atmos. Chem. Phys., 10, 3365–3383, http://dx.doi.org/10.5194/acp-10-3365-2010doi:10.5194/acp-10-3365-2010, 2010.

Saiz-Lopez, A., Plane, J. M C., Mahajan, A S., Anderson, P S., Bauguitte, S. J.-B., Jones, A E., Roscoe, H K., Salmon, R A., Bloss, W J., Lee, J D., and Heard, D E.: On the vertical distribution of boundary layer halogens over coastal Antarctica: implications for O3, HOx, NOx and the Hg lifetime, Atmos. Chem. Phys., 8, 887–900, http://dx.doi.org/10.5194/acp-8-887-2008doi:10.5194/acp-8-887-2008, 2008.

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, http://dx.doi.org/10.5194/acp-3-161-2003doi:10.5194/acp-3-161-2003, 2003.

Schlosser, E., Bohn, B., Brauers, T., Dorn, H., Fuchs, H., Häseler, R., Hofzumahaus, A., Holland, F., Rohrer, F., Rupp, L O., Siese, M., Tillmann, R., and Wahner, A.: Intercomparison of Two Hydroxyl Radical Measurement Techniques at the Atmosphere Simulation Chamber SAPHIR, J. Atmos. Chem., 56, 187–205, http://dx.doi.org/10.1007/s10874-006-9049-3doi:10.1007/s10874-006-9049-3, 2006.

Schlosser, E., Brauers, T., Dorn, H.-P., Fuchs, H., Häseler, R., Hofzumahaus, A., Holland, F., Wahner, A., Kanaya, Y., Kajii, Y., Miyamoto, K., Nishida, S., Watanabe, K., Yoshino, A., Kubistin, D., Martinez, M., Rudolf, M., Harder, H., Berresheim, H., Elste, T., Plass-Dülmer, C., Stange, G., and Schurath, U.: Technical Note: Formal blind intercomparison of OH measurements: results from the international campaign HOxComp, Atmos. Chem. Phys., 9, 7923–7948, http://dx.doi.org/10.5194/acp-9-7923-2009doi:10.5194/acp-9-7923-2009, 2009.

Shao, M., Lu, S., Liu, Y., Xie, X., Chang, C., Huang, S., and Chen, Z.: Volatile organic compounds measured in summer in Beijing and their role in ground-level ozone formation, J. Geophys. Res., 114, D00G06, http://dx.doi.org/10.1029/2008JD010863doi:10.1029/2008JD010863, 2009.

Shirley, T. R., Brune, W. H., Ren, X., Mao, J., Lesher, R., Cardenas, B., Volkamer, R., Molina, L. T., Molina, M. J., 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, http://dx.doi.org/10.5194/acp-6-2753-2006doi:10.5194/acp-6-2753-2006, 2006.

Smith, S C., Lee, J D., Bloss, W J., Johnson, G P., Ingham, T., and Heard, D E.: Concentrations of OH and HO2 radicals during NAMBLEX: measurements and steady state analysis, Atmos. Chem. Phys., 6, 1435–1453, http://dx.doi.org/10.5194/acp-6-1435-2006doi:10.5194/acp-6-1435-2006, 2006.

Sommariva, R., Bloss, W. J., Brough, N., Carslaw, N., Flynn, M., Haggerstone, A.-L., Heard, D. E., Hopkins, J. R., Lee, J. D., Lewis, A. C., McFiggans, G., Monks, P. S., Penkett, S. A., Pilling, M. J., Plane, J. M. C., Read, K. A., Saiz-Lopez, A., Rickard, A. R., and Williams, P. I.: OH and HO2 chemistry during NAMBLEX: roles of oxygenates, halogen oxides and heterogeneous uptake, Atmos. Chem. Phys., 6, 1135–1153, http://dx.doi.org/10.5194/acp-6-1135-2006doi:10.5194/acp-6-1135-2006, 2006.

Stavrakou, T., Peeters, J., and Müller, J.-F.: Improved global modelling of HOx recycling in isoprene oxidation: evaluation against the GABRIEL and INTEX-A aircraft campaign measurements, Atmos. Chem. Phys., 10, 9863–9878, http://dx.doi.org/10.5194/acp-10-9863-2010doi:10.5194/acp-10-9863-2010, 2010.

Steiner, A. L., Cohen, R. C., Harley, R. A., Tonse, S., Millet, D. B., Schade, G. W., and Goldstein, A. H.: VOC reactivity in central California: comparing an air quality model to ground-based measurements, Atmos. Chem. Phys., 8, 351–368, http://dx.doi.org/10.5194/acp-8-351-2008doi:10.5194/acp-8-351-2008, 2008.

Stevens, P S., Mather, J H., and Brune, W H.: Measurement of tropospheric OH and HO2 by laser-induced fluorescence at low pressure, J. Geophys. Res., 99, 3543–3557, 1994.

Stevens, P S., Mather, J H., Brune, W H., Eisele, F., Tanner, D., Jefferson, A., Cantrell, C., Shetter, R., Sewall, S., Fried, A., Henry, B., Williams, E., Baumann, K., Goldan, P., and Kuster, W.: HO2/OH and RO2/HO2 ratios during the Tropospheric OH Photochemistry Experiment: Measurement and theory, J. Geophys. Res., 102, 6379–6391, 1997.

Stockwell, W R., Kirchner, F., Kuhn, M., and Seefeld, S.: A new mechanism for regional atmospheric chemistry modeling, J. Geophys. Res., 102, 25847–25879, 1997.

Taketani, F., Kanaya, Y., and Akimoto, H.: Heterogeneous loss of HO2 by KCl, synthetic sea salt, and natural seawater aerosol particles, Atmos. Environ., 43, 1660–1665, 2009.

Taketani, F., Kanaya, Y., and Akimoto, H.: Kinetics of HO2 Uptake in Levoglucosan and Polystyrene Latex Particles, J. Phys. Chem. Lett., 1, 1701–1704, 2010.

Tan, D., Faloona, I., Simpas, J B., Brune, W., and Shepson, P B.: HO$\rm_x$ budgets in a deciduous forest: Results from the PROPHET summer 1998 campaign, J. Geophys. Res., 106, 24407–24427, 2001.

Taraborrelli, D., Lawrence, M. G., Butler, T. M., Sander, R., and Lelieveld, J.: Mainz Isoprene Mechanism 2 (MIM2): an isoprene oxidation mechanism for regional and global atmospheric modelling, Atmos. Chem. Phys., 9, 2751–2777, http://dx.doi.org/10.5194/acp-9-2751-2009doi:10.5194/acp-9-2751-2009, 2009.

Tas, E., Peleg, M., Matveev, V., Zingler, J., and Luria, M.: Frequency and extent of bromine oxide formation over the Dead Sea, J. Geophys. Res., 110, D11304, http://dx.doi.org/10.1029/2004JD005665doi:10.1029/2004JD005665, 2005.

100

Thornton, J. and Abbatt, J. P D.: Measurements of HO2 uptake to aqueous aerosol: Mass accommodation coefficients and net reactive los, J. Geophys. Res., 110, D08309, http://dx.doi.org/10.1029/2004JD005402doi:10.1029/2004JD005402, 2005.

101

Thornton, J A., Woolridge, P J., Cohen, R C., Martinez, M., Harder, H., Brune, W H., Williams, E J., Roberts, J M., Fehsenfeld, F C., Hall, S R., Shetter, R E., Wert, B P., and Fried, A.: Ozone production rates as a function of NOx abundances and HOx production rates in the Nashville urban plume, J. Geophys. Res., 107, D124146, http://dx.doi.org/10.1029/2001JD000932doi:10.1029/2001JD000932, 2002.

102

Volkamer, R., San Martini, F., Molina, L T., Salcedo, D., Jimenez, J L., and Molina, M J.: A missing sink for gas-phase glyoxal in Mexico City: Formation of secondary organic aerosols, Geophys. Res. Lett., 34, L19807, http://dx.doi.org/10.1029/2007GL030752doi:10.1029/2007GL030752, 2007.

103

Weinstock, B., Niki, H., and Chang, T Y.: Chemical Factors Affecting the Hydroxyl Radical Concentration in the Troposphere, Adv. Environ. Sci. Technol., 10, 221–258, 1980.

104

Whalley, L K., Edwards, P M., Furneaux, K L., Goddard, A., Ingham, T., Evans, M J., Stone, D., Hopkins, J R., Jones, C E., Karunaharan, A., Lee, J D., Lewis, A C., Monks, P S., Moller, S J., and Heard, D E.: Quantifying the magnitude of a missing hydroxyl radical source in a tropical rainforest, Atmos. Chem. Phys., 11, 7223–7233, http://dx.doi.org/10.5194/acp-11-7223-2011doi:10.5194/acp-11-7223-2011, 2011.

105

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. Environ., 40, 7869–7881, 2006.

106

Yue, D L., Hu, M., Wu, Z J., Guo, S., Wen, M T., Nowak, A., Wehner, B., Wiedensohler, A., Takegawa, N., Kondo, Y., Wang, X S., Li, Y P., Zeng, L M., and Zhang, Y H.: Variation of particle number size distributions and chemical compositions at the urban and downwind regional sites in the Pearl River Delta during summertime pollution episodes, Atmos. Chem. Phys., 10, 9431–9439, http://dx.doi.org/10.5194/acp-10-9431-2010doi:10.5194/acp-10-9431-2010, 2010.

107

Zhang, Y H., Hu, M., Zhong, L J., Wiedensohler, A., Liu, S C., Andreae, M O., Wang, W., and Fan, S J.: Regional Integrated Exeriments on Air Quality over Pearl River Delta 2004 (PRIDE-PRD2004): Overview, Atmos. Environ., 42, 6157–6173, 2008.

108

Zhang, Y H., Hu, M., Shao, M., Brauers, T., Chang, C C., Hofzumahaus, A., Holland, F., Li, X., Lu, K., Kita, K., Kondo, Y., Nowak, A., Pöschl, U., Rohrer, F., Zeng, L., Wiedensohler, A., and Wahner, A.: Continuous efforts to investigate regional air pollution in the Pearl River Delta, China: PRiDe PRD2006 campaign, Atmos. Chem. Phys. Discuss., in preparation, 2012.