ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-10187-2010 Coupling of HO<sub>x</sub>, NO<sub>x</sub> and halogen chemistry in the antarctic boundary layer Bloss W. J. 1 Camredon M. 1 6 Lee J. D. 2 Heard D. E. 3 Plane J. M. C. 3 Saiz-Lopez A. 4 Bauguitte S. J.-B. 5 Salmon R. A. 5 Jones A. E. 5 School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK Department of Chemistry, University of York, Heslington, York YO10 5DD, UK School of Chemistry, University of Leeds, Leeds LS2 9JT, UK and National Centre for Atmospheric Science, School of Chemistry, University of Leeds, Leeds LS2 9JT, UK Laboratory for Atmospheric and Climate Science, Consejo Superior de Investigaciones Cientificas (CSIC), Toledo, Spain British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge, CB3 0ET, UK now at: LISA, UMR CNRS/INSU 7583, Université Paris Est Créteil et Université Paris Diderot, Institut Pierre Simon Laplace, 94010 Créteil Cedex, France 01 11 2010 10 21 10187 10209 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/10/10187/2010/acp-10-10187-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/10187/2010/acp-10-10187-2010.pdf

A modelling study of radical chemistry in the coastal Antarctic boundary layer, based upon observations performed in the course of the CHABLIS (Chemistry of the Antarctic Boundary Layer and the Interface with Snow) campaign at Halley Research Station in coastal Antarctica during the austral summer 2004/2005, is described: a detailed zero-dimensional photochemical box model was used, employing inorganic and organic reaction schemes drawn from the Master Chemical Mechanism, with additional halogen (iodine and bromine) reactions added. The model was constrained to observations of long-lived chemical species, measured photolysis frequencies and meteorological parameters, and the simulated levels of HO<sub>x</sub>, NO<sub>x</sub> and XO compared with those observed. The model was able to replicate the mean levels and diurnal variation in the halogen oxides IO and BrO, and to reproduce NO<sub>x</sub> levels and speciation very well. The NO<sub>x</sub> source term implemented compared well with that directly measured in the course of the CHABLIS experiments. The model systematically overestimated OH and HO<sub>2</sub> levels, likely a consequence of the combined effects of (a) estimated physical parameters and (b) uncertainties within the halogen, particularly iodine, chemical scheme. The principal sources of HO<sub>x</sub> radicals were the photolysis and bromine-initiated oxidation of HCHO, together with O(<sup>1</sup>D) + H<sub>2</sub>O. The main sinks for HO<sub>x</sub> were peroxy radical self- and cross-reactions, with the sum of all halogen-mediated HO<sub>x</sub> loss processes accounting for 40% of the total sink. Reactions with the halogen monoxides dominated CH<sub>3</sub>O<sub>2</sub>-HO<sub>2</sub>-OH interconversion, with associated local chemical ozone destruction in place of the ozone production which is associated with radical cycling driven by the analogous NO reactions. The analysis highlights the need for observations of physical parameters such as aerosol surface area and boundary layer structure to constrain such calculations, and the dependence of simulated radical levels and ozone loss rates upon a number of uncertain kinetic and photochemical parameters for iodine species.

 References Allan, B. J. and Plane, J. M. C.: A Study of the Recombination of IO with NO<sub>2</sub> and the Stability of INO<sub>3</sub>: Implications for the Atmospheric Chemistry of Iodine, J. Phys. Chem. A, 106, 8634–8641, 2002. Aranda, A., Le Bras, G., La Verdet, G., and Poulet, G.: The BrO + CH<sub>3</sub>O<sub>2</sub> reaction: Kinetics and role in the atmospheric ozone budget, Geophys. Res. Lett., 24, 2745–2748, 1997. Atkinson, R., Baulch, D. L., Cox, R. A., Crowley, J. N., Hampson, R. F., Hynes, R. G., Jenkin, M. E., Rossi, M. J., and Troe, J.: Evaluated kinetic and photochemical data for atmospheric chemistry: Volume III - gas phase reactions of inorganic halogens, Atmos. Chem. Phys., 7, 981–1191, doi:10.5194/acp-7-981-2007, 2007. Avallone, L. M., Toohey, D. W., Fortin, T. J., McKinney, K. A., and Fuentes, J. D.: In situ measurements of bromine oxide at two high-latitude boundary layer sites: Implications of variability, J. Geophys. Res., 108, 4089, doi:10.1029/2002JD002843, 2003. Bale, C. S. E., Canosa-Mas, C. E., Shallcross, D. E., and Wayne, R. P.: A discharge-flow study of the kinetics of the reactions of IO with CH<sub>3</sub>O<sub>2</sub> and CF<sub>3</sub>O<sub>2</sub>, Phys. Chem. Chem. Phys., 7, 2164–2172, 2005. Bauguitte, S. J.-B., Bloss, W. J., Evans, M. J., Salmon, R. A., Anderson, P. S., Jones, A. E., Lee, J. D., Saiz-Lopez, A., Roscoe, H. K., Wolff, E. W., and Plane, J. M. C.: Summertime NO<sub>x</sub> measurements during the CHABLIS campaign: can source and sink estimates unravel observed diurnal cycles?, Atmos. Chem. Phys. Discuss., 9, 20371–20406, doi:10.5194/acpd-9-20371-2009, 2009. Braban, C. F., Adams, J. W., Rodriguez, D., Cox, R. A., Crowley, J. N., and Schuster, G.: Heterogeneous reactions of HOI, ICl and IBr on sea salt and sea salt proxies, Phys. Chem. Chem. Phys., 9, 3136–3148, 2007. Bloss, W. J., Rowley, D. W., Cox, R. A., and Jones, R. L.: Kinetics and Products of the IO Self-Reaction, J. Phys. Chem. A, 105, 7840–7854, 2001. Bloss, W. J., Lee, J. D., Bloss, C., Heard, D. E., Pilling, M. J., Wirtz, K., Martin-Reviejo, M., and Siese, M.: Validation of the calibration of a laser-induced fluorescence instrument for the measurement of OH radicals in the atmosphere, Atmos. Chem. Phys., 4, 571–583, doi:10.5194/acp-4-571-2004, 2004. Bloss, W. J., Lee, J. D., Johnson, G. P., Heard, D. E., Sommariva, R., Plane, J. M. C., Saiz-Lopez, A., McFiggans, G., Coe, H., Flynn, M., Williams, P., Rickard, A., and Fleming, Z.: Impact of Halogen Monoxide Chemistry upon Boundary Layer OH and HO<sub>2</sub> concentrations at a Coastal Site, Geophys. Res. Lett., 32, L068414, doi:10.1029/2004GL022084, 2005. Bloss, W. J., Lee, J. D., Heard, D. E., Salmon, R. A., Bauguitte, S. J.-B., Roscoe, H. K., and Jones, A. E.: Observations of OH and HO2 radicals in coastal Antarctica, Atmos. Chem. Phys., 7, 4171–4185, doi:10.5194/acp-7-4171-2007, 2007. Boxe, C. S. and Saiz-Lopez, A.: Multiphase modeling of nitrate photochemistry in the quasi-liquid layer (QLL): implications for NOx release from the Arctic and coastal Antarctic snowpack, Atmos. Chem. Phys., 8, 4855–4864, doi:10.5194/acp-8-4855-2008, 2008. Burkholder, J. B., Curtius, J., Ravishankara, A. R., and Lovejoy, E. R.: Laboratory studies of the homogeneous nucleation of iodine oxides, Atmos. Chem. Phys., 4, 19–34, doi:10.5194/acp-4-19-2004, 2004. Butkovskaya, N., Kukui, A. and Le Bras, G.: HNO<sub>3</sub> Forming Channel of the HO<sub>2</sub> + NO Reaction as a Function of Pressure and Temperature in the Ranges of 72–600 Torr and 223–323 K, J. Phys. Chem. A, 111, 9047–9053, 2007. 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, HO<sub>2</sub> and RO<sub>2</sub> radicals in the marine boundary layer 1. Model construction and comparison with field measurements, J. Geophys. Res., 104, 30241–30255, 1999. Chen, G., Davis, D., Crawford, J., Nowak, J.B., Eisele, F., Mauldin III, R L., Tanner, D., Buhr, M., Shetter, R., Lefer, B., Arimoto, R., Hogan, A., and Blake, D.: An Investigation of South Pole HO<sub>x</sub> Chemistry: Comparison of Model Results with ISCAT Observations, Geophys. Res. Lett., 28, 3633–3636, 2001. Chen, G., Davis, D., Crawford, J., Hutterli, L.M., Huey, L.G., Slusher, D., Mauldin, L., Eisele, F., Tanner, D., Dibb, J., Buhr, M., McConnell, J., Lefer, B., Shetter, R., Blake, D., Song, C.H., Lombardo, K., and Arnoldy, J.: A reassessment of HO<sub>x</sub> South Pole chemistry based on observations recorded during ISCAT 2000, Atmos. Environ., 38, 5451–5461, 2004. Chen, G., Huey, L. G., Crawford, J. H., Olson, J. R., Hutterli, M. A., Sjostedt, S., Tanner, D., Dibb, J., Lefer, B., Blake, N, Davis, D., and Stohl, A.: An assessment of the polar HO<sub>x</sub> photochemical budget based on 2003 Summit Greenland field observations, Atmos. Environ., 41, 7806–7820, 2007. Clemitshaw, K. C., Coupling between the Tropospheric Photochemistry of Nitrous Acid (HONO) and Nitric Acid (HNO$_3)$, Environ. Chem., 3, 31–34, 2006. Cotter, E. S. N., Jones, A. E., Wolff, E. W., and Bauguitte, S. J.-B.: What controls photochemical NO and NO2 production from Antarctic snow ? Laboratory investigation assessing the wavelength and temperature dependence. J. Geophys. Res. 108, doi:10.1029/2002JD002602, 2003. Cox, R. A., Bloss, W. J., Jones, R. L., and Rowley, D. M.: OIO and the Atmospheric Cycle of Iodine, Geophys. Res. Lett., 26, 1857–1860, 1999 Crawford, J. H., Davis, D. D., Chen, G., Buhr, M., Oltmans, S., Weller, R., Mauldin, L., Eisele, F., Shetter, R., Lefer, B., Arimoto, R., and Hogan, A.: Evidence for photochemical production of ozone at the South Pole surface, Geophys. Res. Lett., 28, 3641–3644, 2001. Davis, D., Nowak. J. B., Chen, G., Buhr, M., Arimoto, R., Hogan, A., Eisele, F., Mauldin, L., Tanner, D., Shetter, R., Lefer, B., and McMurry, P.: Unexpected High Levels of NO Observed at South Pole, Geophys. Res. Lett., 28, 3625–3628, 2001. Davison, B., Hewitt, C. N., O'Dowd, C., Lowe, J. A., Smith, M. H., Schwikowski, M., Baltensperger, U. and Harrison, R. M.: Dimethyl sulphide, methane sulphonic acid and the physiochemical aerosol properties in Atlantic air from the United Kingdom to Halley Bay, J. Geophys. Res., 101, 22855–22867, 1996. Domine, F., Houdier, S., Taillandier, A.-S., and Simpson, W. R.: Acetaldehyde in the Alaskan subarctic snowpack, Atmos. Chem. Phys., 10, 919–929, doi:10.5194/acp-10-919-2010, 2010. 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. Dillon, T. J., Tucceri, M. E., and Crowley, J. N.: Laser induced fluorescence studies of iodine oxide chemistry, Phys. Chem. Chem. Phys., 8, 5185–5198, 2006. Dillon, T. J., Tucceri, M. E., Sander, R., and J. N. Crowley, LIF Studies of Iodine Oxide Chemistry Part 3. Reactions IO + NO$_3\to$OIO + NO<sub>2</sub>, I + NO$_3\to$IO + NO<sub>2</sub> and CH<sub>2</sub>I + O$_2\to$ (products): implications for the chemistry of the marine atmosphere at night, Phys. Chem. Chem. Phys., 10, 1540–1554, 2008. Drougas, E. and Kosmas, A. M.: Ab Intitio Characterization of (CH<sub>3</sub>IO$_3)$ Isomers and the CH<sub>3</sub>O<sub>2</sub> + IO Reaction Pathways, J. Phys. Chem. A, 111, 3402–3408, 2007. Eisele, F., Davis, D. D., Helming, D., Oltmans, S. J., Neff, W., Huey, G., Tanner, D., Chen, G., Crawford, J., Arimoto, R., Buhr, M., Mauldin, L., Hutterli, M., Dibb, J., Blake, D., Brooks, S. B., Johnson, B., Roberts, J. M., Wang, Y., Tan, D. and Flocke, F.: Antarctic Tropospheric Chemistry Investigation (ANTCI) 2003 overview, Atmos. Environ., 42, 2749–2761, 2008. Enami, S., Yamanaka, T., Hashimoto, S., Kawasaki, M., Nakano, Y., and Ishiwata, T.: Kinetic Study of IO Radical with RO<sub>2</sub> (R = CH<sub>3</sub>, C<sub>2</sub>H$_5$, and CF$_3)$ Using Cavity Rind-Down Spectroscopy, J. Phys. Chem. A, 110, 9861–9866, 2006. Enami, S., Yamanaka, T., Nakayama, T., Hashimoto, S., Kawasaki, M., Shallcross, D. E., Nakano, Y., and Ishiwata, T.: A Gas-Phase Kinetic Study of the Reaction between Bromine Monoxide and Methylperoxy Radicals at Atmospheric Temperatures, J. Phys. Chem. A, 111, 3342–3348, 2007. Evans, M. J., Jacob, D. J., Altlas, E., Cantrell, C. A., Eisele, F., Flocke, F., Fried, A., Mauldin, R. L., Ridley, B. A., Wert, B., Talbot, R., Blake, D., Heikes, B., Snow, J., Walega, J., Weinheimer, A. J., and Dibb, J.: Coupled evolution of BrO$_x$-ClO$_x$-HO<sub>x</sub>-NO<sub>x</sub> chemistry during bromine catalyzed ozone depletion events in the arctic boundary layer, J. Geophys. Res., 108, 8368, doi:10.1029/2002JD002732, 2003. %Fuchs, H., Brauers, T., Dorn, H.-P., Harder, H., Hässler, R., %Hofzumahaus, A., Holland, F., Kanaya, Y., Kajii, Y., Kubistin, D., Lou, S., %Martinez, M., Miyamoto, K., Nishida, S., Rudolf, M., Schlosser, E., Wahner, %A., Yoshino, A., and Schurath, U.: Technical Note: Formal blind %intercomparison of HO<sub>2</sub> measurements in the atmospheric simulation %chamber SAPHIR during the HOxComp campaign, Atmos. Chem. Phys. Discuss., 10, %21189-21235, 2010. Fuchs, H., Brauers, T., Dorn, H.-P., Harder, H., Hässler, R., Hofzumahaus, A., Holland, F., Kanaya, Y., Kajii, Y., Kubistin, D., Lou, S., Martinez, M., Miyamoto, K., Nishida, S., Rudolf, M., Schlosser, E., Wahner, A., Yoshino, A., and Schurath, U.: Technical Note: Formal blind intercomparison of HO<sub>2</sub> measurements in the atmosphere simulation chamber SAPHIR during the HOxComp campaign, Atmos. Chem. Phys. Discuss., 10, 21189–21235, doi:10.5194/acpd-10-21189-2010, 2010. Gómez Martin, J. C., Spietz, P., and Burrows, J. P.: Kinetic and Mechanistic Studies of the I<sub>2</sub>/O<sub>3</sub> Photochemistry, J. Phys. Chem. A, 111, 306–320, 2007. Gómez-Martin, J. C., Ashworth, S. H., Mahajan, A. S., and Plane, J. M. C.: Photochemistry of OIO: Laboratory study and \mboxatmospheric implications, Geophys. Res. Lett., 36, L09802, doi:10.1029/2009GL037642, 2009. Grannas, A., M., Shepson, P. B., Guimbaud, C., Sumner, A. L., Albert, M., Simpson, W., Domine, F., Boudries, H., Bottenheim, J., Beine, H. J., Honrath, R., and Zhou, X.: A study of photochemical and physical processes affecting carbonyl compounds in the Arctic atmospheric boundary layer, Atmos. Environ., 36, 2733–2742, 2002. %Grannas, A. M., Jones, A. E., Dibb, J., Ammann, M., Anastasio, C., Beine, H. %J., Bergin, M., Bottenheim, J., Boxe, C. S., Carver, G., Chen. G., Crawford, %J. H., Dominé, F., Frey, M. M., %Guzmán, M. I., Heard, D. E., Hoffmann, M. R., Honrath, R. E., Huey, L. %G., Hutterli, M., Jacobi, H. W., Klan, P., Lefer, B., McConnell, J., Plane, %J., Sander, R., Savarino, J., Shepson, P. B., Simpson, W. R., Sodeau, J. R., %von Gasow, R., Weller, R., Wolff, E. W., and Zhu, T.: An overview of snow %photochemistry: evidence, mechanisms and impacts, Atmos. Chem. Phys., 7, %4329–4373, 2007. Grannas, A. M., Jones, A. E., Dibb, J., Ammann, M., Anastasio, C., Beine, H. J., Bergin, M., Bottenheim, J., Boxe, C. S., Carver, G., Chen, G., Crawford, J. H., Dominé, F., Frey, M. M., Guzmán, M. I., Heard, D. E., Helmig, D., Hoffmann, M. R., Honrath, R. E., Huey, L. G., Hutterli, M., Jacobi, H. W., Kl$\acute\rm a$n, P., Lefer, B., McConnell, J., Plane, J., Sander, R., Savarino, J., Shepson, P. B., Simpson, W. R., Sodeau, J. R., von Glasow, R., Weller, R., Wolff, E. W., and Zhu, T.: An overview of snow photochemistry: evidence, mechanisms and impacts, Atmos. Chem. Phys., 7, 4329–4373, doi:10.5194/acp-7-4329-2007, 2007. Honrath, R. E., Peterson, M. C., Guo, S., Dibb, J. E., Shepson, P. B., and Campbell, B.: Evidence of NO<sub>x</sub> production within or upon ice particles in the Greenland snowpack, Geophys. Res. Lett., 26, 695–698, 1999. Honrath, R. E., Lu, Y., Peterson, M. C., Dibb, J. E., Arsenault, M. A., Cullen, N. J., and Steffen, K.: Vertical fluxes of NO<sub>x</sub>, HONO, and HNO<sub>3</sub> above the snowpack at Summit, Greenland, Atmos. Environ., 36, 2629–2640, 2002. Houdier, A., Perrier, S., Dominé, F., Cabanes, A., Legagneux, L., Grannas, A. M., Guimbaud, G., Shepson, P. B., Boudries, H., and Bottenheim, J. W.: Acetaldeyhde and acetone in the Arctic snowpack during the ALERT2000 cmapgin. Snowpack composition, incorporation processes and atmospheric impact. Atmos. Environ., 36, 2609–2618, 2002. Hough, A. M.: The calculation of photolysis rates for use in global tropospheric modelling studies, AERE Report R-13259, HMSO, London, UK, 1988. Hutterli, M. A., Röthlisberger, R., and Bales, R. C.: Atmosphere-to-snow-to-firn transfer studies of HCHO at Summit, Greenland, Geophys. Res. Lett., 26, 1691–1694, 1999. Ingham, T., Cameron, M., and Crowley, J. N.: Photodissociation of IO (355 nm) and OIO (532 nm): quantum Yields for O(<sup>3</sup>P) and I(<sup>2</sup>P$_J)$ Production, J. Phys. Chem. A, 104, 8001–8010, 2000. Jacob, D. J.: Heterogeneous chemistry and tropsopheric ozone, Atmos. Environ. 34, 2131–2159, 2000. Jefferson, A., Tanner, D. J., Eisele, F. L., Davis, D. D., Chen, G., Crawford, J., Huey, J. W., Torres, A. L. and Berresheim, H.: OH Photochemistry and methane sulphonic acid formation in the coastal Antarctic boundary layer, J. Geophys. Res., 103, 1647–1656, 1998. Jones, A. E., Weller, R., Wolff, E. W., and Jacobi, H.-W.: Speciation and Rate of Photochemical NO and NO<sub>2</sub> Production in Antarctic Snow, Geophys. Res. Lett., 27, 345–348, 2000. %Jones, A. E., Wolff, E. W., Ames, D., Bauguitte, S. J.-B., Clemitshaw, K. %C., Fleming, Z., Mills, G. P., Saiz-Lopez, A., Salmon, R. A., Sturges, W. %T., and Worton, D. R.: The multi-seasonal NO<sub>y</sub> budget in coastal %Antarctica and its link with surface snow and ice core nitrate: results from %the CHABLIS campaign, Atmos. Chem. Phys. Discuss., 7, 4127-4163, 2007. Jones, A. E., Wolff, E. W., Ames, D., Bauguitte, S. J.-B., Clemitshaw, K. C., Fleming, Z., Mills, G. P., Saiz-Lopez, A., Salmon, R. A., Sturges, W. T., and Worton, D. R.: The multi-seasonal NOy budget in coastal Antarctica and its link with surface snow and ice core nitrate: results from the CHABLIS campaign, Atmos. Chem. Phys. Discuss., 7, 4127–4163, doi:10.5194/acpd-7-4127-2007, 2007. Jones, A. E., Wolff, E. W., Salmon, R. A., Bauguitte, S. J.-B., Roscoe, H. K., Anderson, P. S., Ames, D., Clemitshaw, K. C., Fleming, Z. L., Bloss, W. J., Heard, D. E., Lee, J. D., Read, K. A., Hamer, P., Shallcross, D. E., Jackson, A., Walker, S., Lewis, A. C., Mills, G. P., Plane, J. M. C., Saiz-Lopez, A., Sturges, W. T., and Worton, D. R.: Chemistry of the antarctic boundary layer and the interface with snow: an overview of the CHABLIS campaign, Atmos. Chem. Phys. Discuss., 8, 5137–5181, doi:10.5194/acpd-8-5137-2008, 2008. Joseph, D. M., Ashworth, S. H., and Plane, J. M. C.: The absorption cross-section and photochemistry of OIO, J. Photochem. Photobiol. A: Chemistry, 176, 68–77, 2005. Joseph, D. M., Ashworth, S. H., and Plane, J. M. C.: On the photochemistry of IONO<sub>2</sub>: absorption cross section (240–370 nm) and photolysis product yields at 248 nm, Phys. Chem. Chem. Phys., 9, 5599–5607, 2007. Kaltsoyannis, N. and Plane, J. M. C.: Quantum chemical calculations on a selection of iodine containing species (IO, OIO, INO<sub>3</sub>, (IO)<sub>2</sub>, I<sub>2</sub>O<sub>3</sub>, I<sub>2</sub>O<sub>4</sub> and I<sub>2</sub>O$_5)$ of importance in the atmosphere, Phys. Chem. Chem. Phys., 10, 1723–1733, 2008. Kanaya, Y., Sadanaga, Y., Nakumura, K., and Akimoto, H.: Behavior of OH and HO<sub>2</sub> radicals during the Observations at a Remote Island of Okinawa (ORION99) field campaign: 1. Observation using a laser-induced fluorescence instrument, J. Geophys. Res., 106, 24197–2428, 2001. König-Langlo, G., King, J., and Pettre, P.: Climatology of the three coastal Antarctic stations Dumont d'Urville, Neumayer and Halley, J. Geophys. Res., 103, 10935–10946, 1998. Legrand, M., and Mayewski, P.: Glaciochemistry of Polar Ice Cores: A Review, Rev. Geophys., 35, 219–243, 1997. Lewis, A. C., Carslaw, N., Marriott, P. J., Kinghorn, R. M., Morrison, P., Lee, A. L., Bartle, K. D., and Pilling, M. J.: A larger pool of ozone-forming carbon compounds in urban atmospheres, Nature, 405, 778–781, 2000. 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, doi:10.5194/acp-5-1963-2005, 2005. Liao, W., Case, A. T., Mastromarino, J., Tan, D. and Dibb, J. E.: Observations of HONO by laser-induced fluorescence at the South Pole during ANTCI 2003, Geophys. Res. Lett. 33, L09810, doi:10.1029/2005GL025470, 2006. Madronich, S., and Flocke, S.: The role of solar radiation in atmospheric chemistry, in Handbook of Environmental Chemistry, edited by: Boule, P., Springer_Verlag, Heidelberg, Germany, 1–26, 1998. Mauldin, R., Kosciuch, E., Eisele, F., Huey, G., Tanner, D., Sjostedt, S., Blake, D., Chen, G., Crawford, J., and Davis, D.: South Pole Antarctica observations and modeling results: New insights on HO<sub>x</sub> radical and sulfur chemistry, Atmos. Environ., 44, 572–581, 2010. Maricq, M. M., Szente, J. J., Kaiser, E. W., and Shi, J.: Reaction of Chlorine Atoms with Methyl and Ethylperoxy Radicals, J. Phys. Chem., 98, 2083–2089, 1994. Mauldin III, R. L., Eisele, F. L., Tanner, D. J., Kosciuch, E., Shetter, R., Lefer, B., Hall, S. R., Nowak, J. B., Buhr, M., Chen, G., Wang, P., and Davis, D.: Measurements of OH, H<sub>2</sub>SO<sub>4</sub>, and MSA at the South Pole during ISCAT, Geophys. Res. Lett., 28, 3629–3632, 2001. Mauldin III, R.L., Kosciuch, E., Henry, B., Eisele, F.L., Shetter, R., Lefer, B., Chen, G., Davis, D., Huey, G., and Tanner, D.: Measurements of OH, HO<sub>2</sub> + RO<sub>2</sub>, H<sub>2</sub>SO<sub>4</sub> and MSA at the South Pole during ISCAT 2000, Atmos. Environ., 38, 5423–5437, 2004. McFiggans, G., Plane, J. M. C., Allan, B. J., Carpenter, L. J., Coe, H., and O'Dowd, C.: A modelling study of iodine chemistry in the marine boundary layer, J. Geophys. Res., 105, 14371–14385, 2000. McFiggans, G., Coe, H., Burgess, R., Allan, J., Cubison, M., Alfarra, M. R., Saunders, R., Saiz-Lopez, A., Plane, J. M. C., Wevill, D., Carpenter, L., Rickard, A. R., and Monks, P. S.: Direct evidence for coastal iodine particles from Laminaria macroalgae - linkage to emissions of molecular iodine, Atmos. Chem. Phys., 4, 701–713, doi:10.5194/acp-4-701-2004, 2004. Mössinger, J. C., and Cox, R. A.: Heterogeneous reaction of HOI with sodium halide salts, J. Phys. Chem., A, 105, 5165–5177, 2001. Mössinger, J. C., Rowley, D. M., and Cox, R. A.: The UV-visible absorption cross-sections of IONO<sub>2</sub>, Atmos. Chem. Phys., 2, 227–234, doi:10.5194/acp-2-227-2002, 2002. Oncley, S. P., Buhr, M., Lenschow, D. H., Davis, D., and Semmera, S. R.: Observations of summertime NO fluxes and boundary-layer height at the South Pole during ISCAT 2000 using scalar similarity, Atmos. Environ., 38, 5389–5398, 2004. Orlando, J. J. and Tyndall, G. S.: Rate Coefficients for the Thermal Decomposition of BrONO<sub>2</sub> and the Heat of Formation of BrONO<sub>2</sub>, J. Phys. Chem., 100, 19398–19405, 1996. Plane, J. M. C., Joseph, D. M., Allan, B. J., Ashworth, S. H., and Francisco, J. S.: An Experimental and Theoretical Study of the Reactions OIO + NO and OIO + OH, J. Phys. Chem., 110, 93–100, 2006. Rowley, D. M., Bloss, W. J., Cox, R. A., and Jones, R. L.: Kinetics and Products of the IO + BrO Reaction, J. Phys. Chem. A, 105, 7855–7864, 2001. Read, K. A., Lewis, A. C., Salmon, R. A., Jones, A. E. and Bauguitte, S.: OH and halogen atom influence on the variability of non-methane hydrocarbons in the Antarctic Boundary Layer, Tellus B, 59, 22–38, 2007. Read, K. A., Lewis, A. C., Bauguitte, S., Rankin, A. M., Salmon, R. A., Wolff, E. W., Saiz-Lopez, A., Bloss, W. J., Heard, D. E., Lee, J. D., and Plane, J. M. C.: DMS and MSA measurements in the Antarctic Boundary Layer: impact of BrO on MSA production, Atmos. Chem. Phys., 8, 2985–2997, doi:10.5194/acp-8-2985-2008, 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 during the PMTACS-NY 2001 campaign in New York City, Atmos. Environ., 37, 3627–3637, 2003. Riedel, K., Weller, R., and Schrems, O.: Variability of formaldehyde in the Antarctic troposphere, Phys. Chem. Chem. Phys., 1, 5523–5527, 1999. Saiz-Lopez, A. and Boxe, C. S.: A mechanism for biologically-induced iodine emissions from sea-ice, Atmos. Chem. Phys. Discuss., 8, 2953–2976, doi:10.5194/acpd-8-2953-2008, 2008. Saiz-Lopez, A., Mahajan, A. S., Salmon, R. A., Bauguitte, S. J.-B., Jones, A. E., Roscoe, H. K., and Plane, J. M. C.: Boundary layer halogens in coastal Antarctica, Science, 317, 348–351, 2007a. Saiz-Lopez, A., Chance, K., Liu, X., Kurosu, T. P., and Sander, S. P.: First observations of iodine oxide from space, Geophys. Res. Lett., 34, L12812, doi:10.1029/2007GL030111, 2007b 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, doi:10.5194/acp-8-887-2008, 2008. Salmon, R. A., Bauguitte, S. J.-B., Bloss, W., Hutterli, M. A., Jones, A. E., Read, K., and Wolff, E. W.: Measurement and interpretation of gas phase formaldehyde concentrations obtained during the CHABLIS campaign in coastal Antarctica, Atmos. Chem. Phys., 8, 4085–4093, doi:10.5194/acp-8-4085-2008, 2008. Sander, S. P., Friedl, R. R., Golden, D. M., Kurylo, M. J., Moortgat, G. K., Keller-Rudek, H., 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, NASA-JPL Publication 06-2, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 2006. Saunders, R. W. and Plane, J. M. C.: Formation Pathways and Composition of Iodine Oxide Ultra-Fine Particles, Environ. Chem., 2, 299–303, 2005. 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-D�lmer, 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, doi:10.5194/acp-9-7923-2009, 2009. %Schönhardt, A., Richter, A., Wittrock, F., Kirk, H., Oetjen, H., Roscoe, %H. K., and Burrows, J. P.: Observations of iodine monoxide columns from %satellite. Atmos. Chem. Phys., 8, 637-653, 2008. Schönhardt, A., Richter, A., Wittrock, F., Kirk, H., Oetjen, H., Roscoe, H. K., and Burrows, J. P.: Observations of iodine monoxide columns from satellite, Atmos. Chem. Phys., 8, 637–653, doi:10.5194/acp-8-637-2008, 2008. 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, doi:10.5194/acp-6-2753-2006, 2006. Simpson, W. R., von Glasow, R., Riedel, K., Anderson, P., Ariya, P., Bottenheim, J., Burrows, J., Carpenter, L. J., Frieß, U., Goodsite, M. E., Heard, D., Hutterli, M., Jacobi, H.-W., Kaleschke, L., Neff, B., Plane, J., Platt, U., Richter, A., Roscoe, H., Sander, R., Shepson, P., Sodeau, J., Steffen, A., Wagner, T., and Wolff, E.: Halogens and their role in polar boundary-layer ozone depletion, Atmos. Chem. Phys., 7, 4375–4418, doi:10.5194/acp-7-4375-2007, 2007. Sjostedt, S. J., Huey, L. G., Tanner, D. J., Peischl, J., Chen, G., Dibb, J. E., Lefer, B., Hutterli, M. A., Beyersdorf, A. J., Blake, N. J., Blake, D. R., Sueper, D., Ryerson, T., Burkhart, J., and Stohl, A.: Observations of hydroxyl and the sum of peroxy radicals at Summit, Greenland during summer 2003, Atm. Environ., 41, 5122–5137, 2007. %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., and Williams, P. I.: OH and HO<sub>2</sub> %chemistry during NAMBLEX: roles of oxygenates, halogen oxides and %heterogeneous uptake, Atmos. Chem. Phys., 6, 1135, 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, doi:10.5194/acp-6-1135-2006, 2006. Sumner, A.-L., and Shepson, P. B.: Snowpack production of formaldehyde and its effect on the Arctic troposphere, Nature, 398, 230–233, 1999. Tan. D., Faloona, I., Simpas, J. B., Brune, W., Olson, J., Crawford, J., Avery, M., Sachse, G., Vay, S., Sandholm, S., Guan, H.-W., Vaughn, T., Mastromarino, J., Heikes, B., Snow, J., Podolske, J., and Singh, H.: OH and HO<sub>2</sub> in the tropical Pacific: Results from PEM-Tropics B, J. Geophys. Res., 106, 32667–32681, 2001. Tucceri, M. E., Hölscher, D., Rodriguez, A., Dillon, T. J., and Crowley, J. N.: Absorption cross section and photolysis of OIO, Phys. Chem. Chem. Phys. 8, 834–846, 2006. Wagenbach, D., Ducroz, F., Mulvaney, R., Keck, L., Minikin, A., LeGrand, M., Hall, J. S., and Wolff, E. W.: Sea-salt aerosol in coastal Antarctic regions, J. Geophys. Res. 103, 10961–10974, 1998. Wolff, E. W.: Nitrate in Polar Ice, in: Ice core studies of global biogeochemical cycles, edited by: Delmas, R. J., Springer-Verlag, Berlin, Germany, 195–224, 1995. Van den Bergh, H. and Troe, J.: Kinetic and thermodynamic properties of INO and INO<sub>2</sub> intermediate complexes in iodine recombination, J. Chem. Phys., 64, 736–742, 1976. Vogt, R., Sander, R., von Glasow, R., and Crutzen, P. J.: Iodine Chemistry and its Role in Halogen Activation and Ozone Loss in the Marine Boundary Layer: A Model Study, J. Atmos. Chem., 32, 375–395, 1999. von Glasow, R. and Crutzen, P. J.: Tropospheric Halogen Chemistry, Treatise on Geochemistry, 4, 1–67, 2007. Wang, Y., Choi, Y., Zeng, T., Davis, D., Buhr, M., Huey, L. G., and Neff, W.: Assessing the photochemical impact of snow NO<sub>x</sub> emissions over Antarctica during ANTCI 2003, Atmos. Environ., 42, 2849–2863, 2008. Zhou, X., Beine, H., Honrath, R. E., Fuentes, J. D., Simpson, W., Shepson, P. B., and Bottenheim, J. W.: Snowpack Photochemical Production of HONO: a Major source of OH in the Arctic Boundary Layer in Springtime, Geophys. Res. Lett., 28, 4087–4090, 2001.