ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-10-28635-2010 Global observations of tropospheric BrO columns using GOME-2 satellite data Theys N. 1 Van Roozendael M. 1 Hendrick F. 1 Yang X. 2 3 De Smedt I. 1 Richter A. 4 Begoin M. 4 Errera Q. 1 Johnston P. V. 5 Kreher K. 5 De Mazière M. 1 Belgian Institute for Space Aeronomy (IASB-BIRA), Brussels, Belgium National Centre for Atmospheric Science (NCAS), Cambridge, CB2 1EW, UK Centre for Atmospheric Science, Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, UK Institute of Environmental Physics, University of Bremen, Bremen, Germany National Institute of Water and Atmospheric Research (NIWA), Omakau, Central Otago, New Zealand 22 11 2010 10 11 28635 28685 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-discuss.net/10/28635/2010/acpd-10-28635-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/10/28635/2010/acpd-10-28635-2010.pdf

Measurements from the GOME-2 satellite instrument have been analyzed for tropospheric BrO using a residual technique that combines measured BrO columns and estimates of the stratospheric BrO content from a climatological approach driven by O<sub>3</sub> and NO<sub>2</sub> observations. Comparisons between the GOME-2 results and BrO vertical columns derived from correlative ground-based and SCIAMACHY nadir observations, present a good level of consistency. We show that the adopted technique enables separation of stratospheric and tropospheric fractions of the measured total BrO columns and allows quantitative study of the BrO plumes in polar regions. While some satellite observed plumes of enhanced BrO can be explained by stratospheric descending air, we show that most BrO hotspots are of tropospheric origin, although they are often associated to regions with low tropopause heights as well. Elaborating on simulations using the $p$-TOMCAT tropospheric chemical transport model, this result is found to be consistent with the mechanism of bromine release through sea salt aerosols production during blowing snow events. Outside polar regions, evidence is provided for a global tropospheric BrO background with column of 1–3×10<sup>13</sup> molec/cm<sup>2</sup>, consistent with previous estimates.

 References Afe O. T., Richter, A., Sierk, B., Wittrock, F., and Burrows, J. P.: BrO emissions from volcanoes: a survey using GOME and SCIAMACHY measurements, Geophys. Res. Lett., 31, L24113, doi:10.1029/2004GL0200994, 2004. Aliwell, S. R., Van Roozendael, M., Johnston, P. V., Richter, A., Wagner, T., Arlander, D. W., Burrows, J. P., Fish, D. J., Jones, R. L., Tornkvist, K. K., and Lambert, J. C., Pfeilsticker, K., and Pundt, I.: Analysis for BrO in zenith-sky spectra: An intercomparison exercise for analysis improvement, J. Geophys. Res., 107, D140, doi:10.1029/2001JD000329, 2002. Begoin, M., Richter, A., Weber, M., Kaleschke, L., Tian-Kunze, X., Stohl, A., Theys, N., and Burrows, J. P.: Satellite observations of long range transport of a large BrO plume in the Arctic, Atmos. Chem. Phys., 10, 6515–6526, doi:10.5194/acpd-10-6515-2010, 2010. Bobrowski, N., Hönninger, G., Galle, B., and Platt, U.: Detection of bromine monoxide in a volcanic plume, Nature, 423, 273–276, 2003. Boersma, K. F., Eskes, H. J., and Brinksma, E. J.: Error analysis for tropospheric NO<sub>2</sub> retrieval from space, J. Geophys. Res., 109, D04311, doi:10.1029/2003JD003962, 2004. Bogumil, K., Orphal, J., Homann, T., Voigt, S., Spietz, P., Fleischmann, O.C., Vogel, A., Hartmann, M., Bovensmann, H., Frerik, J., and Burrows, J. P.: Measurements of molecular absorption spectra with the SCIAMACHY Pre-Flight Model: Instrument characterization and reference spectra for atmospheric remote sensing in the 230–2380 nm region, J. Photochem. Photobiol. A, 157, 167–184, 2003. Bovensmann, H., Burrows, J. P., Buchwitz, M., Frerick, J., No\"el, S., Rozanov, V. V., Chance, K. V., Goede, A. P. H.: SCIAMACHY: Mission objectives and Measurement Modes, J. Atmos. Sci., 56, 127–150, 1999. Brion, J., Chakir, A., Daumont, D., and Malicet, J.: High-resolution laboratory absorption cross sections of O<sub>3</sub> Temperature effect, Chem. Phys. Lett., 213(5–6), 610–612, 1993. Burrows, J. P., Dehn, A., Deters, B., Himmelmann, S., Richter, A., Voigt, S., and Orphal, J.: Atmospheric Remote-Sensing Reference Data from GOME: 1. Temperature-Dependent Absorption Cross Sections of NO<sub>2</sub> in the 231–794 nm Range, J. Quant. Spectrosc. Radiat. Transfer, 60, 1025, 1998. Chance, K.: Analysis of BrO measurements from the Global Ozone Monitoring Experiment, Geophys. Res. Lett., 25, 3335–3338, 1998. De Smedt, I., Müller, J.-F., Stavrakou, T., van der A, R., Eskes, H., and Van Roozendael, M.: Twelves years of global observations of formaldehyde in the troposphere using GOME and SCIAMACHY sensors, Atmos. Chem. Phys., 8, 4947–4963, doi:10.5194/acp-8-4947-2008, 2008. Dorf, M., Butz, A., Camy-Peyret, C., Chipperfield, M. P., Kritten, L., and Pfeilsticker, K.: Bromine in the tropical troposphere and stratosphere as derived from balloon-borne BrO observations, Atmos. Chem. Phys., 8, 7265–7271, doi:10.5194/acp-8-7265-2008, 2008. EUMETSAT, GOME-2 FM3 Calibration: Instrument Performance Testing, MO-TR-TPD-GO-0094. Fitzenberger, R., Bösch, H., Camy-Peyret, C., Chipperfield, M. P., Harder, H., Platt, U., Sinnhuber, B.-M., Wagner, T., and Pfeilsticker, K.: First profile measurements of tropospheric BrO, Geophys. Res. Lett., 27, 2921–2924, 2000. Fleischmann, O. C., Hartmann, M., Burrows J. P., and Orphal, J.: New ultraviolet absorption cross-sections of BrO at atmospheric temperatures measured by time-windowing Fourier transform spectroscopy, J. Photochem. Photobiol. A, 168, 117–132, 2004. Frieß, U., Hollwedel, J., König-Langlo, G., Wagner, T., and Platt, U.: Dynamics and chemistry of tropospheric bromine explosion events in the Antarctic coastal region, J. Geophys. Res., 109, D06305, doi:10.1029/2003JD004133, 2004. Grainger, J. F. and Ring, J.: Anomalous Fraunhofer lines profiles, Nature, 193, p 762, 1962. Harder, H., Camy-Peyret, C., Ferlemann, F., Fitzenberger, R., Hawat, T., Osterkamp, H., Perner, D., Platt, U., Schneider, M., Vradelis, P., and Pfeilsticker, K.: Stratospheric BrO Profiles Measured at Different Latitudes and Seasons: Atmospheric Observations, Geophys. Res. Lett., 25, 3843–3846, 1998. Hausmann, M. and Platt, U.: Spectroscopic measurement of bromine oxide and ozone in the high Arctic during Polar Sunrise Experiment 1992, J. Geophys. Res., 99, 25399–25414, 1994. Hebestreit, K., Stutz, J., Rosen, D., Matveiv, V., Peleg, M., Luria, M., and Platt, U.: DOAS measurements of tropospheric bromine oxide in mid-latitudes, Science, 283, 55–57, 1999. Hendrick, F., Van Roozendael, M., Chipperfield, M. P., Dorf, M., Goutail, F., Yang, X., Fayt, C., Hermans, C., Pfeilsticker, K., Pommereau, J.-P., Pyle, J. A., Theys, N., and De Mazière, M.: Retrieval of stratospheric and tropospheric BrO profiles and columns using ground-based zenith-sky DOAS observations at Harestua, 60° N, Atmos. Chem. Phys., 7, 4869–4885, doi:10.5194/acp-7-4869-2007, 2007. Hendrick, F., Johnston, P. V., De Mazière, M., Fayt, C., Hermans, C., Kreher, K., Theys, N., and Van Roozendael, M.: One-decade trend analysis of stratospheric BrO over Harestua (60° N) and Lauder (45° S) reveals a decline, Geophys. Res. Lett., 35, L14801, doi:10.1029/2008GL034154, 2008. Hendrick, F., Rozanov, A., Johnston, P. V., Bovensmann, H., De Mazière, M., Fayt, C., Hermans, C., Kreher, K., Lotz, W., Sinnhuber, B.-M., Theys, N., Thomas, A., Burrows, J. P., and Van Roozendael, M.: Multi-year comparison of stratospheric BrO vertical profiles retrieved from SCIAMACHY limb and ground-based UV-visible measurements, Atmos. Meas. Tech., 2, 273–285, doi:10.5194/amt-2-273-2009, 2009. Hollwedel, J.: Observations of Tropospheric and Stratospheric Bromine Monoxide from Satellite, PhD. Thesis, University of Heidelberg, Germany, 2005. Hönninger, G. and Platt, U.: Observations of BrO and its vertical distribution during surface ozone depletion at Alert, Atmos. Environ., 36, 2481-2489, 2002. Jones, A. E., Anderson, P., Begoin, M., Brough, N., Hutterli, M., Marshall, G., Richter, A., Roscoe, H., and Wolff, E.: BrO, blizzards, and drivers of polar tropospheric ozone depletion events, Atmos. Chem. Phys., 9, 4639–4652, doi:10.5194/acp-9-4639-2009, 2009. Jones, A. E., Anderson, P., Wolff, E., Roscoe, H., Marshall, G., Richter, A., Brough, N., and Colwell, S.: Vertical structure of Antarctic tropospheric ozone depletion events: characteristics and broader implications, Atmos. Chem. Phys., 10, 7775–7794, doi:10.5194/acp-10-7775-2010, 2010. Kaleschke, L., Richter, A., Burrows, J. P., Afe, O., Heygster, G., Notholt, J., Rankin, A. M., Roscoe, H. K., Hollwedel, J., Wagner, T., and Jacobi, H.-W.: Frost flowers on sea ice as a source of sea salt and their influence on tropospheric halogen chemistry, Geophys. Res. Lett., 31, L16114, doi:10.1029/2004GL020655, 2004. Koelemeijer, R. B. A., Stammes, P., Hovenier, J. W., and de Haan, J. F.: Global distributions of effective cloud fraction and cloud top pressure derived from oxygen A band spectra measured by the Global Ozone Monitoring Experiment: comparison to ISCCP data, J. Geophys. Res., 107, 4151, doi:10.1029/2001JD000840, 2002. Koelemeijer, R. B. A., de Haan, J. F., and Stammes, P.: A database of spectral surface reflectivity in the range 335-772 nm derived from 5.5 years of GOME observations, J. Geophys. Res.-Atmos., 108(D2), 4070, doi:10.1029/2002JD002429, 2003. Kreher, K., Johnston, P. V., Wood, S. W., Nardi, B., and Platt, U.: Ground-based measurements of tropospheric and stratospheric BrO at Arrival Heights, Antarctica, Geophys. Res. Lett., 24, 3021–3024, 1997. Lary, D. J.: Gas phase atmospheric bromine photochemistry, J. Geophys. Res., 101, 1505–1516, 1996. Lary, D. J.: Halogens and the chemistry of the free troposphere, Atmos. Chem. Phys., 5, 227–237, doi:10.5194/acp-5-227-2005, 2005. Leser, H., Höninger, G., and Platt, U.: Max-DOAS measurements of BrO and NO<sub>2</sub> in the marine boundary layer, Geophys. Res. Lett., 30, 1537, doi:10.1029/2002GL015811, 2003. Martin, R. V., Chance, K., Jacob, D. J., Kurosu, T. P., Spurr, R. J. D., Bucsela, E., Gleason, J. F., Palmer, P. I., Bey, I., Fiore, A. M., Li, Q., Yantosca, R. M., and Koelemeijer, R. B. A.: An improved retrieval of tropospheric nitrogen dioxide from GOME, J. Geophys. Res., 107(D20), 4437, doi:10.1029/2001JD001027, 2002. Mayer, B. and Kylling, A.: Technical note: The libRadtran software package for radiative transfer calculations – description and examples of use, Atmos. Chem. Phys., 5, 1855–1877, doi:10.5194/acp-5-1855-2005, 2005. McConnel, J. C., Henderson, G. S., Barrie, L., Bottenheim, J., Niki, H., Langford, C. H., and Templeton, E. M. J.: Photochemical bromine production implicated in Arctic boundary-layer ozone depletion, Nature, 355, 150-152, 1992. McElroy, M. B., Salawitch, R. J., Wofsy, S. C., and Logan, J. A.: Reductions of Antarctic ozone due to synergetic interactions of chlorine and bromine, Nature, 321, 759–762, 1986. Meller, R. and Moortgat, G. K.: Temperature dependence of the absorption cross-section of HCHO between 223 and 323 K in the wavelength range 225-375 nm, J. Geophys. Res., 105(D6), 7089–7102, doi:10.1029/1999JD901074, 2000. Montzka, S. A., Butler, J. H., Hall, B. D., Mondeel, D. J., and Elkins, J. W.: A decline in tropospheric organic bromine, Geophys. Res. Lett., 30(15), 1826, doi:10.1029/2003GL017745, 2003. Munro, R., Eisinger, M., Anderson, C., Callies, J., Corpaccioli, E., Lang, R., Lefebvre, A., Livschitz, Y., and Albinana, A. P.: GOME-2 on MetOp, in: Proc. of The 2006 EUMETSAT Meteorological Satellite Conference, Helsinki, Finland, 12–16 June 2006, EUMETSAT P.48, 2006. Oppenheimer, C., Tsanev, V. I., Braban, C. F, Cox, R. A., Adams, J. W., Aiuppa, A., Bobrowski, N., Delmelle, P., Barclay, J., and McGonigle, A. J.: BrO formation in volcanic plumes, Geochim. Cosmochim. Acta, 70, 2935–2941, 2006. Palmer, P. I., Jacob, D. J., Chance, K., Martin, R. V., Spurr, R. J. D., Kurosu, T. P., Bey, I., Yantosca, R., Fiore, A., and Li, Q.: Air-mass factor formulation for spectroscopic measurements from satellites~: application to formaldehyde retrievals from GOME, J. Geophys. Res., 106(D13), 14539–14550, doi:10.1029/2000JD900772, 2001. Platt, U. and Stutz, J.: Differential Optical Absorption Spectroscopy (DOAS), Principle and Applications, ISBN 3-340-21193-4, Springer Verlag, Heidelberg, Germany, 2008. Read, K. A., Mahajan, A. S., Carpenter, L. J., Evans, M. J., et al.: Extensive halogen-mediated ozone destruction over the tropical Atlantic Ocean, Nature, 453, 1232-1235, 2008. Richter, A.: Absorptionspektroskopische Messungen stratosphärischer Spurengase über Bremen, 55° N, PhD thesis, Inst. für Umweltphysik, Univ. Bremen, Bremen, Germany, 1997. Richter, A., Wittrock, F., Eisinger, M., and Burrows, J. P.: GOME Observations of Tropospheric BrO in Northern Hemispheric Spring and Summer 1997, Geophys. Res. Lett., 25, 2683–2686, 1998. Richter, A., Wittrock, F., Ladstätter-Weissenmayer, A., and Burrows, J. P.: GOME measurements of stratospheric and tropospheric BrO, Adv. Space Res., 29, 1667–1672, 2002. Richter, A., Burrows, J. P., Nüß, H., Granier, C, Niemeier, U.: Increase in tropospheric nitrogen dioxide over China observed from space, Nature, 437, 129–132, doi:10.1038/nature04092, 2005. Rodgers, C. D.: Inverse Methods for Atmospheric Sounding, Theory and Practice, World Scientific Publishing, Singapore-New-Jersey-London-Hong Kong, 2000. Rozanov, A., Rozanov, V., and Burrows, J. P.: A numerical radiative transfer model for a spherical planetary atmosphere: Combined differential integral approach involving the Piccard iterative approximation, J. Quant. Spectrosc. Radiat. Transfer, 69, 491–512, 2001. Saiz-Lopez, A., Plane, J. M. C., and Shilito, J. A.: Bromine oxide in the mid-latitude marine boundary layer, Geophys. Res. Lett., 31, L03111, doi:10.1029/2003GL018956, 2004. Salawitch, R. J., Canty, T., Kurosu, T., Chance, K., Liang, Q., da Silva, A., Pawson, S., Nielsen, J. E., Rodriguez, J. M., Bhartia, P. K., Liu, X., Huey, L. G., Liao, J., Stickel, R. E., Tanner, D.J., Dibb, J .E., Simpson, W. R., Donohoue, D., Weinheimer, A., Flocke, F., Knapp, D., Montzka, D., Neuman, J. A., Nowak, J. B., Ryerson, T. B., Oltmans, S., Blake, D. R., Atlas, E. L., Kinnison, D. E., Tilmes, S., Pan, L.L., Hendrick, F., Van Roozendael, M., Kreher, K., Johnston, P. V., Gao, R. S., Johnson, B., Bui, T. P., Chen, G., Pierce, R. B., Crawford, J. H., and Jacob, D. J: A new interpretation of total column BrO during Arctic Spring, Geophys. Res. Lett. (Frontier Articles), 37, L21805, doi:10.1029/2010GL043798, 2010. :A new interpretation of total column BrO during Arctic Spring, Geophys. Res. Lett. (Frontier Articles), L21805, doi:10.1029/2010GL043798, 2010. Schoeberl, M. R.: Extratropical stratosphere-troposphere mass exchange, J. Geophys. Res., 109, D13303, doi: 10.1029/2004JD004525, 2004. Schofield, R., Kreher, K., Connor, B. J., Johnston, P. V., Thomas, A., Shooter, D., Chipperfield, M. P., Rodgers, C. D., and Mount, G. H.: Retrieved tropospheric and stratospheric BrO columns over Lauder, New Zealand., J. Geophys. Res., 109, D14304, doi:10.1029/2003JD004463, 2004. Schofield, R., Johnston, P. V., Thomas, A., Kreher, K., Connor, B. J., Wood, S., Shooter, D., Chipperfield, M. P., Richter, A., von Glasow, R., and Rodgers, C. D.: Tropospheric and stratospheric BrO columns over Arrival Heights, Antartica, 2002, J. Geophys. Res., 111, D22310, doi:10.1029/2005JD007022, 2006. Schroeder, W. H., Anlauf, K. G., Barrie, L. A., Lu, J. Y., Steffen, A., Scheenberger, D. R., and Berg, T.: Arctic springtime depletion of mercury, Nature, 394, 331–332, 1998. Siddans, R., Latter, B. G., Kerridge, B. J., Smeets, J., Otter, G., and Slijkhuis, S.: Analysis of GOME-2, Slit function Measurements Final Report, Eumetsat Contract No. EUM/CO/04/1298/RM, 2006. Simpson, W. R., von Glasow, R., Riedel, K., Anderson, P., Ariya, P., Bottenheim, J., Burrows, J. P., Carpenter, L., 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. Sinnhuber, B.-M., Rozanov, A., Sheode, N., Afe, O. T., Richter, A., Sinnhuber, M., Wittrock, F., Stiller, G. P., von Clarmann, T., Linden, A., and Burrows, J. P.: Global observations of stratospheric bromine monoxide from SCIAMACHY, Geophys. Res. Lett., 32, L20810, doi:10.1029/2005GL023839, 2005. Theys, N., Van Roozendael, M., Hendrick, F., Fayt, C., Hermans, C., Baray, J.-L., Goutail, F., Pommereau, J.-P., and De Mazière, M.: Retrieval of stratospheric and tropospheric BrO columns from multi-axis DOAS measurements at Reunion Island (21° S, 56° E), Atmos. Chem. Phys., 7, 4733–4749, 2007. Theys, N., Van Roozendael, M., Dils, B., Hendrick, F., Hao, N., and De Mazière, M.: First satellite detection of volcanic bromine monoxide emission after the Kasatochi eruption, Geophys. Res. Lett., 36, L03809, doi:10.1029/2008GL036552, 2009a. Theys, N., Van Roozendael, M., Errera, Q., Hendrick, F., Daerden, F., Chabrillat, S., Dorf, M., Pfeilsticker, K., Rozanov, A., Lotz, W., Burrows, J. P., Lambert, J.-C., Goutail, F., Roscoe, H. K., and De Mazière, M.: A global stratospheric bromine monoxide climatology based on the BASCOE chemical transport model, Atmos. Chem. Phys., 9, 831–848, doi:10.5194/acp-9-831-2009, 2009b. Van Roozendael, M., Wagner, T., Richter, A., Pundt, I., Arlander, D., Burrows, J. P., Chipperfield, M., Fayt, C., Johnston, P. V., Lambert, J.-C., Kreher, K., Pfeilsticker, K., Platt, U., Pommereau, J.-P., Sinnhuber, B.-M., Tornkvist, K. K., and Wittrock, F.: Intercomparison of BrO measurements from ERS-2 GOME, ground-based and balloon platforms, Adv. Space Res., 29, 1661–1666, 2002. Van Roozendael, M., De Smedt, I., Fayt, C., Wittrock, F., Richter, A., Afe, O.: First validation of SCIAMACHY BrO columns, in Proc. Second Workshop on the Atmospheric Chemistry Validation of ENVISAT (ACVE-2), Frascati, Italy, 3–7 May, 2004. Vogt, R., Crutzen, P. J., and Sander, P.: A mechanism for halogen release from sea-salt aerosol in the remote marine boundary layer, Nature, 383, 327-330, 1996. von Glasow, R., von Kuhlmann, R., Lawrence, M. G., Platt, U., and Crutzen, P. J.: Impact of reactive bromine chemistry in the troposphere, Atmos. Chem. Phys., 4, 2481–2497, doi:10.5194/acp-4-2481-2004, 2004. von Glasow, R., and Crutzen, P. J.: Tropospheric halogen chemistry in the atmosphere, edited by: Keeling, R.F., vol.4., Treatise on Geochemistry, edited by: Holland, H.D. and Turekian, K.K., 1-67, Elsevier-Pergamon, Oxford, 2007. Vountas, M., Rozanov, V. V., and Burrows, J. P.: Ring effect: Impact of rotational raman scattering on radiative transfer in earth's atmosphere, J. Quant. Spectrosc. Radiat. Transfer., 60, 943–961, 1998. Wagner, T. and Platt, U.: Satellite mapping of enhanced BrO concentrations in the troposphere, Nature, 395, 486–490, 1998. Wagner, T., Leue, C., Wenig, M., Pfeilsticker, K., and Platt, U.: Spatial and temporal distribution of enhanced boundary layer BrO concentrations measured by the GOME instrument aboard ERS-2, J. Geophys. Res., 106, 24225–24236, 2001. Wang, P., Stammes, P., van der A, R., Pinardi, G., and Van Roozendael, M.: FRESCO+: an improved O<sub>2</sub> A-band cloud retrieval algorithm for tropospheric trace gas retrieval, Atmos. Chem. Phys., 8, 6565–6576, doi:10.5194/acp-8-6565-2008, 2008. Wennberg, P.: Atmospheric chemistry: Bromine explosion, Nature, 397, 299–301, 1999. World Meteorological Organization (WMO): Scientific Assessment of Ozone Depletion: 2006, Global ozone research and monitoring project, Chapter 2: Halogenated Very Short-Lived Substances, Rep. 50, Geneva, Switzerland, 2007. Yang, X., Cox, R. A., Warwick, N. J., Pyle, J. A., Carver, G. D., O'Connor, F. M., and Savage, N. H.: Tropospheric bromine chemistry and its impacts on ozone: A model study, J. Geophys. Res., 110, D23311, doi:10.1029/2005JD006244, 2005. Yang, X., Pyle, J. A., and Cox, R. A.: Sea salt aerosol production and bromine release: Role of snow on sea ice, Geophys. Res. Lett., 35, L16815, doi:10.1029/2008GL034536, 2008. Yang, X., Pyle, J. A., Cox, R. A., Theys, N., Van Roozendael, M.: Snow-sourced bromine and its implications for polar tropospheric ozone, Atmos. Chem. Phys., 10, 7763–7773, doi:10.5194/acp-10-7763-2010, 2010. Ziemke, J. R., Chandra, S., and Bhartia, P. K.: "Cloud slicing": A new technique to derive upper tropospheric ozone from satellite measurements, J. Geophys. Res., 106(D9), 9853–9867, 2001.