ACPD Atmospheric Chemistry and Physics Discussions ACPD Atmos. Chem. Phys. Discuss. 1680-7375 Göttingen, Germany 10.5194/acpd-10-28687-2010 Temperature thresholds for polar stratospheric ozone loss Drdla K. 1 Müller R. 2 NASA Ames Research Center, Moffett Field, CA, USA Institute for Energy and Climate Research (IEK-7), Research Centre Jülich, 52425 Jülich, Germany 23 11 2010 10 11 28687 28720 Copyright: © 2010 K. Drdla 2010 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/preprints/10/28687/2010/acpd-10-28687-2010.html The full text article is available as a PDF file from https://acp.copernicus.org/preprints/10/28687/2010/acpd-10-28687-2010.pdf

Low stratospheric temperatures are known to be responsible for heterogeneous chlorine activation that leads to polar ozone depletion. Here, we discuss the temperature threshold below which substantial chlorine activation occurs. We suggest that the onset of chlorine activation is dominated by reactions on cold binary aerosol particles, without formation of polar stratospheric clouds (PSCs), i.e. without significant uptake of HNO<sub>3</sub> from the gas-phase. Using reaction rates on cold binary aerosol, a chlorine activation threshold temperature, T<sub>ACL</sub>, is derived. At typical stratospheric conditions, T<sub>ACL</sub> is similar in value to T<sub>NAT</sub> the highest temperature at which nitric acid trihydrate (NAT) can theoretically condense to form PSCs. T<sub>ACL</sub> is still in use as parameterization for the threshold temperature for the onset of chlorine activation. However, perturbations can cause T<sub>ACL</sub> to differ from T<sub>NAT</sub>: T<sub>ACL</sub> is dependent upon H<sub>2</sub>O, potential temperature, and the sulphate aerosol loading, but unlike T<sub>NAT</sub> is not dependent upon HNO<sub>3</sub>. A parameterization of T<sub>ACL</sub> is provided here, allowing it to be calculated over a comprehensive range of stratospheric conditions. Although considering T<sub>ACL</sub> as a proxy for chlorine activation can be no substitute for a detailed model calculation, T<sub>ACL</sub> provides a more accurate description of the temperature conditions necessary for polar ozone depletion than T<sub>NAT</sub> and can readily be used in place of T<sub>NAT</sub>.

 References Abbatt, J. P.&nbsp;D. and Molina, M.&nbsp;J.: Heterogeneous interactions of ClONO<sub>2</sub> and HCl on nitric acid trihydrate at 202 K, J. Phys. Chem., 96, 7674–7679, 1992. Bauman, J.&nbsp;J., Russel, P.&nbsp;B., Geller, M.&nbsp;A., and Hamill, P.: A stratospheric aerosol climatology from SAGE II and CLAES measurements: 2. Results and comparisons, 1884–1999, J.&nbsp;Geophys. Res., 108, 4383, <a href="http://dx.doi.org/10.1029/2002JD002993">https://doi.org/10.1029/2002JD002993</a>, 2003. Buchholz, J.: Simulations of physics and chemistry of polar stratospheric clouds with a general circulation model, Ph.D. thesis, University of Mainz, Germany, <a href="http://ubm.opus.hbz-nrw.de/volltexte/2005/818/pdf/diss.pdf">http://ubm.opus.hbz-nrw.de/volltexte/2005/818/pdf/diss.pdf</a>, 2005. Carslaw, K.&nbsp;S. and Peter, T.: Uncertainties in reactive uptake coefficients for solid stratospheric particles – 1. Surface chemistry, Geophys. Res. Lett., 24, 1743–1746, 1997. Carslaw, K.&nbsp;S., Luo, B.&nbsp;P., Clegg, S.&nbsp;L., Peter, T., Brimblecombe, P., and Crutzen, P.&nbsp;J.: Stratospheric aerosol growth and HNO<sub>3</sub> gas phase depletion from coupled HNO<sub>3</sub> and water uptake by liquid particles, Geophys. Res. Lett., 21, 2479–2482, <a href="http://dx.doi.org/10.1029/94GL02799">https://doi.org/10.1029/94GL02799</a>, 1994. Carslaw, K.&nbsp;S., Luo, B.&nbsp;P., and Peter, T.: An analytical expression for the composition of aqueous HNO<sub>3</sub>-H<sub>2</sub>SO<sub>4</sub>-H<sub>2</sub>O stratospheric aerosols including gas phase removal of HNO<sub>3</sub>, Geophys. Res. Lett., 22, 1877–1880, <a href="http://dx.doi.org/10.1029/95GL01668">https://doi.org/10.1029/95GL01668</a>, 1995. Carslaw, K.&nbsp;S., Peter, T., and Clegg, S.&nbsp;L.: Modeling the composition of liquid stratospheric aerosols, Rev. Geophys., 35, 125–154, 1997{a}. Carslaw, K.&nbsp;S., Peter, T., and Müller, R.: Uncertainties in Reactive Uptake Coefficients for Solid Stratospheric Particles – 2. Effect on Ozone Depletion, Geophys. Res. Lett., 24, 1747–1750, 1997{b}. Chipperfield, M.&nbsp;P., Cariolle, D., and Simon, P.: A 3D transport model study of chlorine activation during EASOE, Geophys. Res. Lett., 21, 1467–1470, <a href="http://dx.doi.org/10.1029/93GL01679">https://doi.org/10.1029/93GL01679</a>, 1994. Chipperfield, M.&nbsp;P., Feng, W., and Rex, M.: Arctic ozone loss and climate sensitivity: {U}pdated three-dimensional model study, Geophys. Res. Lett., 32, L11813, <a href="http://dx.doi.org/10.1029/2005GL022674">https://doi.org/10.1029/2005GL022674</a>, 2005. Cox, R.&nbsp;A., MacKenzie, A.&nbsp;R., Müller, R.&nbsp;H., Peter, T., and Crutzen, P.&nbsp;J.: Activation of stratospheric chlorine by reactions in liquid sulphuric acid, Geophys. Res. Lett., 21, 1439–1442, 1994. Crutzen, P.&nbsp;J.: Albedo enhancements by stratospheric sulfur injections: a contribution to resolve a policy dilemma? An Editorial Essay, Clim. Change, 77, 211–219, 2006. Crutzen, P.&nbsp;J., Müller, R., Brühl, C., and Peter, T.: On the potential importance of the gas phase reaction $\mathrm{CH_3O_2 + ClO \to \mathrm{ClOO + CH_3O}$} and the heterogeneous reaction $\mathrm{HOCl + HCl \to \mathrm{H_2O + Cl_2}$} in "ozone hole" chemistry, Geophys. Res. Lett., 19, 1113–1116, <a href="http://dx.doi.org/10.1029/92GL01172">https://doi.org/10.1029/92GL01172</a>, 1992. Davies, S., Chipperfield, M.&nbsp;P., Carslaw, K.&nbsp;S., Sinnhuber, B.-M., Anderson, J.&nbsp;G., Stimpfle, R.&nbsp;M., Wilmouth, D.&nbsp;M., Fahey, D.&nbsp;W., Popp, P.&nbsp;J., Richard, E.&nbsp;C., von&nbsp;der Gathen, P., Jost, H., and Webster, C.&nbsp;R.: Modeling the effect of denitrification on {A}rctic ozone depletion during winter 1999/2000, J.&nbsp;Geophys. Res., 107, 8322, <a href="http://dx.doi.org/10.1029/2001JD000445">https://doi.org/10.1029/2001JD000445</a>, (printed 108(D5), 2003), 2002. Davies, S., Mann, G. W., Carslaw, K. S., Chipperfield, M. P., Kettleborough, J. A., Santee, M. L., Oelhaf, H., Wetzel, G., Sasano, Y., and Sugita, T.: 3-D microphysical model studies of Arctic denitrification: comparison with observations, Atmos. Chem. Phys., 5, 3093–3109, https://doi.org/10.5194/acp-5-3093-2005, 2005. Del Negro, L.&nbsp;A., Fahey, D.&nbsp;W., Donnelly, S.&nbsp;G., Gao, R.&nbsp;S., Keim, E.&nbsp;R., Wamsley, R.&nbsp;C., Woodbridge, E.&nbsp;L., Dye, J.&nbsp;E., Baumgardner, D., Gandrud, B.&nbsp;W., Wilson, J.&nbsp;C., Jonsson, H.&nbsp;H., Loewenstein, M., Podolske, J.&nbsp;R., Webster, C.&nbsp;R., May, R.&nbsp;D., Worsnop, D.&nbsp;R., Tabazadeh, A., Tolbert, M.&nbsp;A., Kelly, K.&nbsp;K., and Chan, K.&nbsp;R.: Evaluating the role of NAT, NAD, and liquid H<sub>2</sub>SO<sub>4</sub>/H<sub>2</sub>O/HNO<sub>3</sub> solutions in {A}ntarctic polar stratospheric cloud aerosol: {O}bservations and implications, J.&nbsp;Geophys. Res., 102, 13255–13282, 1997. Deshler, T., Bryan, B.&nbsp;J., Hofmann, D.&nbsp;J., and Nardi, B.: Correlation between ozone loss and volcanic aerosol at altitudes below 14 km over McMurdo Station, Antarctica, Geophys. Res. Lett., 21, 2931–2934, 1996. Douglass, A.&nbsp;R., Schoeberl, M.&nbsp;R., Stolarski, R.&nbsp;S., Waters, J.&nbsp;W., Russell III, J.&nbsp;M., Roche, A.&nbsp;E., and Massie, S.&nbsp;T.: Interhemispheric differences in springtime production of HCl and ClONO<sub>2</sub> in the polar vortices, J.&nbsp;Geophys. Res., 100, 13967–13978, 1995. Douglass, A.&nbsp;R., Stolarski, R.&nbsp;S., Strahan, S.&nbsp;E., and Polansky, B.&nbsp;C.: Sensitivity of {A}rctic ozone loss to polar stratospheric cloud volume and chlorine and bromine loading in a chemistry and transport model, Geophys. Res. Lett., 33, L17809, <a href="http://dx.doi.org/10.1029/2006GL026492">https://doi.org/10.1029/2006GL026492</a>, 2006. Drdla, K.: Temperature thresholds for polar stratospheric ozone, Eos Trans. AGU, 86, Fall Meet. Suppl., Abstract A31D–03, 2005. Drdla, K. and Schoeberl, M.&nbsp;R.: Microphysical modeling of the 1999–2000 Arctic winter 2. {C}hlorine activation and ozone depletion, J.&nbsp;Geophys. Res., 107, 8319, <a href="http://dx.doi.org/10.1029/2001JD001159">https://doi.org/10.1029/2001JD001159</a>, (printed 108 (D5), 2003), 2002. Drdla, K., Schoeberl, M.&nbsp;R., and Browell, E.&nbsp;V.: Microphysical modeling of the 1999–2000 Arctic winter 1. {P}olar stratospheric clouds, denitrification, and dehydration, J.&nbsp;Geophys. Res., 107, 8312, <a href="http://dx.doi.org/10.1029/2001JD000782">https://doi.org/10.1029/2001JD000782</a>, (printed 108 (D5), 2003), 2002. Dye, J., Gandrud, B., Baumgardner, D., Chan, K., Ferry, G., Loewenstein, M., Kelly, K., and Wilson, J.: Observed particle evolution in the polar stratospheric cloud of {J}anuary 24, 1989, Geophys. Res. Lett., 17, 413–416, 1990. Dye, J.&nbsp;E., Baumgardner, D., Gandrud, B.&nbsp;W., Kawa, S.&nbsp;R., Kelly, K.&nbsp;K., Loewenstein, M., Ferry, G.&nbsp;V., Chan, K.&nbsp;R., and Gary, B.&nbsp;L.: Particle size distributions in Arctic polar stratospheric clouds, growth and freezing of sulfuric acid droplets and implications for cloud formation, J.&nbsp;Geophys. Res., 97, 8015–8034, 1992. Engel, A., Müller, R., Schmidt, U., Carslaw, K.&nbsp;S., and Stachnik, R.&nbsp;A.: Indications of heterogeneous chlorine activation on moderately cold aerosol based on chlorine observations in the Arctic stratosphere, Atmos. Environ., 34, 4283–4289, 2000. Eskes, H., van Velthoven, P., Valks, P., and Kelder, H.: Assimilation of GOME total ozone satellite observations in a three-dimensional tracer-transport model, Q.&nbsp;J.&nbsp;R. Meteorol. Soc., 129, 1663–1682, 2003. Eskes, H.&nbsp;J., Segers, A., and van Velthoven, P.: Ozone forecasts of the stratospheric polar vortex splitting event in {S}eptember 2002, J.&nbsp;Atmos. Sci., 62, 812–821, 2005. Eyring, V., Waugh, D.&nbsp;W., Bodeker, G.&nbsp;E., Cordero, E., Akiyoshi, H., Austin, J., Beagley, S.&nbsp;R., Boville, B.&nbsp;A., Braesicke, P., Brühl, C., Butchart, N., Chipperfield, M.&nbsp;P., Dameris, M., Deckert, R., Deushi, M., Frith, S.&nbsp;M., Garcia, R.&nbsp;R., Gettelman, A., Giorgetta, M.&nbsp;A., Kinnison, D.&nbsp;E., Mancini, E., Manzini, E., Marsh, D.&nbsp;R., Matthes, S., Nagashima, T., Newman, P.&nbsp;A., Nielsen, J.&nbsp;E., Pawson, S., Pitari, G., Plummer, D.&nbsp;A., Rozanov, E., Schraner, M., Scinocca, J.&nbsp;F., Semeniuk, K., Shepherd, T.&nbsp;G., Shibata, K., Steil, B., Stolarski, R.&nbsp;S., Tian, W., and Yoshiki, M.: Multimodel projections of stratospheric ozone in the 21st century, J.&nbsp;Geophys. Res., 112, D16303, <a href="http://dx.doi.org/10.1029/2006JD008332">https://doi.org/10.1029/2006JD008332</a>, 2007. Eyring, V., Sheperd, T.&nbsp;G., and Waugh, D.&nbsp;W., eds.: SPARC report on the evaluation of chemistry-climate models, SPARC Rep. No. 5, WRCP-132, WMO-TD No. 1526, World Meteorol. Organ., Geneva, 2010. Fahey, D.&nbsp;W., Gao, R.&nbsp;S., Carslaw, K.&nbsp;S., Kettleborough, J., Popp, P.&nbsp;J., Northway, M.&nbsp;J., Holecek, J.&nbsp;C., Ciciora, S.&nbsp;C., McLaughlin, R.&nbsp;J., Thompson, T.&nbsp;L., Winkler, R.&nbsp;H., Baumgardner, D.&nbsp;G., Gandrud, B., Wennberg, P.&nbsp;O., Dhaniyala, S., McKinley, K., Peter, T., Salawitch, R.&nbsp;J., Bui, T.&nbsp;P., Elkins, J.&nbsp;W., Webster, C.&nbsp;R., Atlas, E.&nbsp;L., Jost, H., Wilson, J.&nbsp;C., Herman, R.&nbsp;L., Kleinböhl, A., and von König, M.: The detection of large HNO}<sub>3</sub>-containing particles in the winter {Arctic stratosphere, Science, 291, 1026–1031, 2001. Farman, J.&nbsp;C., Gardiner, B.&nbsp;G., and Shanklin, J.&nbsp;D.: Large losses of total ozone in Antarctica reveal seasonal ClO<sub>x</sub>/NO<sub>x</sub> interaction, Nature, 315, 207–210, 1985. Feck, T., Groo{ß}, J.-U., and Riese, M.: Sensitivity of A}rctic ozone loss to stratospheric {H<sub>2</sub>O, Geophys. Res. Lett., 35, L01803, <a href="http://dx.doi.org/10.1029/2007GL031334">https://doi.org/10.1029/2007GL031334</a>, 2008. Garcia, R.&nbsp;R., Marsh, D.&nbsp;R., Kinnison, D.&nbsp;E., Boville, B.&nbsp;A., and Sassi, F.: Simulation of secular trends in the middle atmosphere, 1950–2003, J.&nbsp;Geophys. Res., 112, D09301, <a href="http://dx.doi.org/10.1029/2006JD007485">https://doi.org/10.1029/2006JD007485</a>, 2007. Geer, A.&nbsp;J., Lahoz, W.&nbsp;A., Bekki, S., Bormann, N., Errera, Q., Eskes, H.&nbsp;J., Fonteyn, D., Jackson, D.&nbsp;R., Juckes, M.&nbsp;N., Massart, S., Peuch, V.-H., Rharmili, S., and Segers, A.: The ASSET intercomparison of ozone analyses: method and first results, Atmos. Chem. Phys., 6, 5445–5474, <a href="http://dx.doi.org/10.5194/acp-6-5445-2006">https://doi.org/10.5194/acp-6-5445-2006</a>, 2006. Groo{ß}, J.-U., Pierce, R.&nbsp;B., Crutzen, P.&nbsp;J., Grose, W.&nbsp;L., and Russell III, J.&nbsp;M.: Re-formation of chlorine reservoirs in southern hemisphere polar spring, J.&nbsp;Geophys. Res., 102, 13141–13152, <a href="http://dx.doi.org/10.1029/96JD03505">https://doi.org/10.1029/96JD03505</a>, 1997. Groo{ß}, J.-U., Günther, G., Müller, R., Konopka, P., Bausch, S., Schlager, H., Voigt, C., Volk, C. M., and Toon, G. C.: Simulation of denitrification and ozone loss for the Arctic winter 2002/2003, Atmos. Chem. Phys., 5, 1437–1448, https://doi.org/10.5194/acp-5-1437-2005, 2005. Hadjinicolaou, P., Pyle, J.&nbsp;A., Chipperfield, M.&nbsp;P., and Kettleborough, J.&nbsp;A.: Effect of interannual meteorological variability on mid-latitude O<sub>3</sub>, Geophys. Res. Lett., 24, 2993–2996, 1997. Hanisco, T.&nbsp;F., Smith, J.&nbsp;B., Stimpfle, R.&nbsp;M., Wilmouth, D.&nbsp;M., Perkins, K.&nbsp;K., Spackman, J.&nbsp;R., Anderson, J.&nbsp;G., Baumgardner, D., Gandrud, B., Webster, C.&nbsp;R., Dhaniyala, S., McKinney, K.&nbsp;A., and Bui, T.&nbsp;P.: Quantifying the rate of heterogeneous processing in the A}rctic polar vortex with in situ observations of {OH, J.&nbsp;Geophys. Res., 107, 8278, <a href="http://dx.doi.org/10.1029/2001JD000425">https://doi.org/10.1029/2001JD000425</a>, 2002. Hanson, D.&nbsp;R. and Mauersberger, K.: Laboratory studies of the nitric acid trihydrate: Implications for the south polar stratosphere, Geophys. Res. Lett., 15, 855–858, <a href="http://dx.doi.org/10.1029/88GL00209">https://doi.org/10.1029/88GL00209</a>, 1988. Hanson, D.&nbsp;R. and Ravishankara, A.&nbsp;R.: Reaction of ClONO<sub>2</sub> with HCl on NAT, NAD, and frozen sulfuric acid and hydrolysis of N<sub>2</sub>O<sub>5</sub> and ClONO<sub>2</sub> on frozen sulfuric acid, J.&nbsp;Geophys. Res., 98, 22931–22936, 1993. Hanson, D.&nbsp;R., Ravishankara, A.&nbsp;R., and Solomon, S.: Heterogeneous reactions in sulfuric acid aerosols: A framework for model calculations, J.&nbsp;Geophys. Res., 99, 3615–3629, 1994. Hitchcock, P., Shepherd, T. G., and McLandress, C.: Past and future conditions for polar stratospheric cloud formation simulated by the Canadian Middle Atmosphere Model, Atmos. Chem. Phys., 9, 483–495, https://doi.org/10.5194/acp-9-483-2009, 2009. Hofmann, D. and Oltmans, S.: Anomalous {A}ntarctic ozone during 1992: {E}vidence for {P}inatubo volcanic aerosol effects, J.&nbsp;Geophys. Res., 98, 18555–18561, 1993. Hofmann, D.&nbsp;J. and Solomon, S.: Ozone destruction through heterogeneous chemistry following the eruption of El Chich{ó}n, J.&nbsp;Geophys. Res., 94, 5029–5041, 1989. Hoppel, K., Nedoluha, G., Fromm, M., Allen, D., Bevilacqua, R., Alfred, J., Johnson, B., and König-Langlo, G.: Reduced ozone loss at the upper edge of the {A}ntarctic Ozone Hole during 2001–2004, Geophys. Res. Lett., 32, L20816, <a href="http://dx.doi.org/10.1029/2005GL023968">https://doi.org/10.1029/2005GL023968</a>, 2005. IPCC/TEAP: Special Report on Safeguarding the Ozone Layer and the Global Climate System: {I}ssues Related to Hydrofluorocarbons and Perfluorocarbons, edited by: Metz, B., Kuijpers, L., Solomon, S., Andersen, S. O., Davidson, O., Pons, J., de Jager, D., Kestin, T., Manning, M., and Meyer, L., Cambridge University Press, Cambridge, United Kingdom, and New York, NY, USA, 2005. Jones, A.&nbsp;E. and Shanklin, J.&nbsp;D.: Continued decline of total ozone over {H}alley, {A}ntarctica, since 1985, Nature, 376, 409–411, 1995. Jones, R.&nbsp;L., McKenna, D.&nbsp;S., Poole, L.&nbsp;R., and Solomon, S.: On the influence of polar stratospheric cloud formation on chemical composition during the 1988/89 arctic winter, Geophys. Res. Lett., 17, 545–548, 1990. Kawa, S.&nbsp;R., Newman, P.&nbsp;A., Lait, L.&nbsp;R., Schoeberl, M.&nbsp;R., Stimpfle, R.&nbsp;M., Kohn, D.&nbsp;W., Webster, C.&nbsp;R., May, R.&nbsp;D., Baumgardner, D., Dye, J.&nbsp;E., Wilson, J.&nbsp;C., Chan, K.&nbsp;R., and Loewenstein, M.: Activation of chlorine in sulfate aerosol as inferred from aircraft observations, J.&nbsp;Geophys. Res., 102, 3921–3933, 1997. Kettleborough, J.&nbsp;A., Carver, G.&nbsp;D., Lary, D.&nbsp;J., Pyle, J.&nbsp;A., and Scott, P.&nbsp;A.: Three dimensional modelling of chlorine activation in the {A}rctic stratosphere, Geophys. Res. Lett., 21, 1471–1474, <a href="http://dx.doi.org/10.1029/93GL03048">https://doi.org/10.1029/93GL03048</a>, 1994. Kiesewetter, G., Sinnhuber, B.-M., Vountas, M., Weber, M., and Burrows, J.&nbsp;P.: A long term stratospheric ozone data set from assimilation of satellite observations: {H}igh latitude ozone anomalies, J.&nbsp;Geophys. Res., 115, D10307, <a href="http://dx.doi.org/10.1029/2009JD013362">https://doi.org/10.1029/2009JD013362</a>, 2010. Knudsen, B. M., Harris, N. R. P., Andersen, S. B., Christiansen, B., Larsen, N., Rex, M., and Naujokat, B.: Extrapolating future Arctic ozone losses, Atmos. Chem. Phys., 4, 1849–1856, https://doi.org/10.5194/acp-4-1849-2004, 2004. Krämer, M., Müller, R.&nbsp;I., Bovensmann, H., Burrows, J., Brinkmann, J., Röth, E.&nbsp;P., Groo{ß}, J.&nbsp;U., Müller, R.&nbsp;O., Woyke, T.&nbsp;H., Ruhnke, R., Günther, G., Hendricks, J., Lippert, E., Carslaw, K.&nbsp;S., Peter, T., Zieger, A., Brühl, C.&nbsp;H., Steil, B., Lehmann, R., and McKenna, D.&nbsp;S.: Intercomparison of stratospheric chemistry models under polar vortex conditions, J.&nbsp;Atmos. Chem., 45, 51–77, <a href="http://dx.doi.org/10.1023/A:1024056026432">https://doi.org/10.1023/A:1024056026432</a>, 2003. Kühl, S., Dörnbrack, A., Wilms-Grabe, W., Sinnhuber, B.-M., Platt, U., and Wagner, T.: Observational evidence of rapid chlorine activation by mountain waves above northern {S}candinavia, J.&nbsp;Geophys. Res., 109, D22309, <a href="http://dx.doi.org/10.1029/2004JD004797">https://doi.org/10.1029/2004JD004797</a>, 2004. Lowe, D. and MacKenzie, A.&nbsp;R.: Polar stratospheric cloud microphysics and chemistry, J.&nbsp;Atmos. Solar Terr. Phys., 70, 13–40, <a href="http://dx.doi.org/10.1016/j.jastp.2007.09.011">https://doi.org/10.1016/j.jastp.2007.09.011</a>, 2008. Manney, G.&nbsp;L., Froidevaux, L., Santee, M.&nbsp;L., Livesey, N.&nbsp;J., Sabutis, J.&nbsp;L., and Waters, J.&nbsp;W.: Variability of ozone loss during A}rctic winter (1991 to 2000) estimated from {UARS {Microwave} {L}imb {S}ounder measurements, J.&nbsp;Geophys. Res., 108, 4149, <a href="http://dx.doi.org/10.1029/2002JD002634">https://doi.org/10.1029/2002JD002634</a>, 2003. McElroy, M.&nbsp;B., Salawitch, R.&nbsp;J., Wofsy, S.&nbsp;C., and Logan, J.&nbsp;A.: Antarctic ozone: {R}eductions due to synergistic interactions of chlorine and bromine, Nature, 321, 759–762, 1986. Molina, L.&nbsp;T. and Molina, M.&nbsp;J.: Production of Cl<sub>2</sub>O<sub>2</sub> from the selfreaction of the ClO radical, J.&nbsp;Phys. Chem., 91, 433–436, 1987. Müller, R., Crutzen, P.&nbsp;J., Oelhaf, H., Adrian, G.&nbsp;P., v. Clarmann, T., Wegner, A., Schmidt, U., and Lary, D.: Chlorine chemistry and the potential for ozone depletion in the Arctic stratosphere in the winter of 1991/92, Geophys. Res. Lett., 21, 1427–1430, 1994. Northway, M.&nbsp;J., Gao, R.&nbsp;S., Popp, P.&nbsp;J., Holecek, J.&nbsp;C., Fahey, D.&nbsp;W., Carslaw, K.&nbsp;S., Tolbert, M.&nbsp;A., Lait, L.&nbsp;R., Dhaniyala, S., Flagan, R.&nbsp;C., Wennberg, P.&nbsp;O., Mahoney, M.&nbsp;J., Herman, R.&nbsp;L., Toon, G.&nbsp;C., and Bui, T.&nbsp;P.: An analysis of large HNO<sub>3</sub>-containing particles sampled in the {A}rctic stratosphere during the winter of 1999/2000, J.&nbsp;Geophys. Res., 107, 8298, <a href="http://dx.doi.org/10.1029/2001JD001079">https://doi.org/10.1029/2001JD001079</a>, 2002. Peter, T.: Microphysics and heterogeneous chemistry of polar stratospheric clouds, Ann. Rev. Phys. Chem., 48, 785–822, 1997. Pitari, G., Mancini, E., Rizi, V., and Shindell, D.&nbsp;T.: Impact of future climate and emission changes on stratospheric aerosols and ozone, J.&nbsp;Atmos. Sci., 59, 414–440, 2002. Pitts, M. C., Thomason, L. W., Poole, L. R., and Winker, D. M.: Characterization of Polar Stratospheric Clouds with spaceborne lidar: CALIPSO and the 2006 Antarctic season, Atmos. Chem. Phys., 7, 5207–5228, https://doi.org/10.5194/acp-7-5207-2007, 2007. Pitts, M.&nbsp;C., Poole, L.&nbsp;R., Dörnbrack, A., and Thomason, L.&nbsp;W.: The 2009–2010 Arctic polar stratospheric cloud season: A {CALIPSO} perspective, Atmos. Chem. Phys. Discuss., in press, 2010. Pitts, M. C., Poole, L. R., and Thomason, L. W.: CALIPSO polar stratospheric cloud observations: second-generation detection algorithm and composition discrimination, Atmos. Chem. Phys. Discuss., 9, 8121–8157, https://doi.org/10.5194/acpd-9-8121-2009, 2009. Portmann, R.&nbsp;W., Solomon, S., Garcia, R.&nbsp;R., Thomason, L.&nbsp;W., Poole, L.&nbsp;R., and McCormick, M.&nbsp;P.: Role of aerosol variations in anthropogenic ozone depletion in the polar regions, J.&nbsp;Geophys. Res., 101, 22991–23006, 1996. Prather, M.&nbsp;J.: More rapid ozone depletion through the reaction of HOCl with HCl on polar stratospheric clouds, Nature, 355, 534–537, 1992. Rasch, P.&nbsp;J., Tilmes, S., Turco, R.&nbsp;P., Robock, A., Oman, L., and Chen, C.-C.: An overview of geoengineering of climate using stratospheric sulphate aerosols, Proc. R. Soc. London&nbsp;A, 366, 4007–4037, <a href="http://dx.doi.org/10.1098/rsta.2008.0131">https://doi.org/10.1098/rsta.2008.0131</a>, 2008. Ravishankara, A.&nbsp;R. and Hanson, D.&nbsp;R.: Differences in the reactivity of Type I polar stratospheric clouds depending on their phase, J.&nbsp;Geophys. Res., 101, 3885–3890, 1996. Rex, M., Salawitch, R.&nbsp;J., von&nbsp;der Gathen, P., Harris, N. R.&nbsp;P., Chipperfield, M.&nbsp;P., and Naujokat, B.: {A}rctic ozone loss and climate change, Geophys. Res. Lett., 31, L04116, <a href="http://dx.doi.org/10.1029/2003GL018844">https://doi.org/10.1029/2003GL018844</a>, 2004. Sander, S.&nbsp;P., Friedl, R.&nbsp;R., Golden, D.&nbsp;M., Kurylo, M.&nbsp;J., Huie, R.&nbsp;E., Orkin, V.&nbsp;L., Moortgat, G.&nbsp;K., Wine, P.&nbsp;H., Ravishankara, A.&nbsp;R., Kolb, C.&nbsp;E., Molina, M.&nbsp;J., and Finlayson-Pitts, B.&nbsp;J.: Evaluation number 15, Chemical kinetics and photochemical data for use in atmospheric studies, NASA Panel for Data Evaluation, JPL Publication 06–2, Jet Propulsion Laboratory, California Insitute of Technology, Pasadena, California, 2006. Santee, M.&nbsp;L., Manney, G.&nbsp;L., Froidevaux, L., Zurek, R.&nbsp;W., and Waters, J.&nbsp;W.: MLS observations of ClO and HNO<sub>3</sub> in the 1996-97 {A}rctic polar vortex, Geophys. Res. Lett., 24, 2713–2716, 1997. Santee, M.&nbsp;L., MacKenzie, I.&nbsp;A., Manney, G.&nbsp;L., Chipperfield, M.&nbsp;P., Bernath, P.&nbsp;F., Walker, K.&nbsp;A., Boone, C.&nbsp;D., Froidevaux, L., Livesey, N.&nbsp;J., and Waters, J.&nbsp;W.: A study of stratospheric chlorine partitioning based on new satellite measurements and modeling, J.&nbsp;Geophys. Res., 113, D12307, <a href="http://dx.doi.org/10.1029/2007JD009057">https://doi.org/10.1029/2007JD009057</a>, 2008. Schlager, H., Arnold, F., Hofmann, D.&nbsp;J., and Deshler, T.: Balloon observations of nitric acid aerosol formation in the Arctic stratosphere: I Gaseous nitric acid, Geophys. Res. Lett., 17, 1275–1278, <a href="http://dx.doi.org/10.1029/90GL01621">https://doi.org/10.1029/90GL01621</a>, 1990. Shi, Q., Jayne, J.&nbsp;T., Kolb, C.&nbsp;E., Worsnop, D.&nbsp;R., and Davidovits, P.: Kinetic model for reaction of ClONO<sub>2</sub> with H<sub>2</sub>O and HCl and HOCl with HCl in sulfuric acid solutions, J.&nbsp;Geophys. Res., 106, 24259–24274, <a href="http://dx.doi.org/10.1029/2000JD000181">https://doi.org/10.1029/2000JD000181</a>, 2001. Shindell, D.&nbsp;T. and de Zafra, R.&nbsp;L.: Limits on heterogeneous processing in the Antarctic spring vortex from a comparison of measured and modeled chlorine, J.&nbsp;Geophys. Res., 102, 1441–1449, 1997. Solomon, S.: Stratospheric ozone depletion: A review of concepts and history, Rev. Geophys., 37, 275–316, <a href="http://dx.doi.org/10.1029/1999RG900008">https://doi.org/10.1029/1999RG900008</a>, 1999. Solomon, S., Garcia, R.&nbsp;R., Rowland, F.&nbsp;S., and Wuebbles, D.&nbsp;J.: On the depletion of Antarctic ozone, Nature, 321, 755–758, 1986. Solomon, S., Portmann, R.&nbsp;W., Sasaki, T., Hofmann, D.&nbsp;J., and Thompson, D. W.&nbsp;J.: Four decades of ozonesonde measurements over Antarctica, J.&nbsp;Geophys. Res., 110, D21311, <a href="http://dx.doi.org/10.1029/2005JD005917">https://doi.org/10.1029/2005JD005917</a>, 2005. Stolarski, R.&nbsp;S., Krueger, A.&nbsp;J., Schoeberl, M.&nbsp;R., McPeters, R.&nbsp;D., Newman, P.&nbsp;A., and Alpert, J.&nbsp;C.: Nimbus 7 satellite measurements of the springtime Antarctic ozone decrease, Nature, 322, 808–811, 1986. Tilmes, S., M{ü}ller, R., Groo{ß}, J.-U., and Russell, J.&nbsp;M.: Ozone loss and chlorine activation in the {A}rctic winters 1991–2003 derived with the tracer-tracer correlations, Atmos. Chem. Phys., 4, 2181–2213, 2004. Tilmes, S., Kinnison, D., Müller, R., Sassi, F., Marsh, D., Boville, B., and Garcia, R.: Evaluation of heterogeneous processes in the polar lower stratosphere in the Whole Atmosphere Community Climate Model, J.&nbsp;Geophys. Res., 112, D24301, <a href="http://dx.doi.org/10.1029/2006JD008334">https://doi.org/10.1029/2006JD008334</a>, 2007. Tilmes, S., Müller, R., and Salawitch, R.&nbsp;J.: The sensitivity of polar ozone depletion to proposed geoengineering schemes, Science, 320, 1201–1204, <a href="http://dx.doi.org/10.1126/science.1153966">https://doi.org/10.1126/science.1153966</a>, 2008{a}. Tilmes, S., Müller, R., Salawitch, R.&nbsp;J., Schmidt, U., Webster, C.&nbsp;R., Oelhaf, H., Russell III, J.&nbsp;M., and Camy-Peyret, C.&nbsp;C.: Chemical ozone loss in the A}rctic winter 1991–1992, Atmos. Chem. Phys., 8, 1897–1910, 2008{b. Tilmes, S., Garcia, R.&nbsp;R., Kinnison, D.&nbsp;E., Gettelman, A., and Rasch, P.&nbsp;J.: Impact of geoengineered aerosols on the troposphere and stratosphere, J.&nbsp;Geophys. Res., 114, D12305, <a href="http://dx.doi.org/10.1029/2008JD011420">https://doi.org/10.1029/2008JD011420</a>, 2009. Toohey, D.&nbsp;W., Avallone, L.&nbsp;M., Lait, L.&nbsp;R., Newman, P.&nbsp;A., Schoeberl, M.&nbsp;R., Fahey, D.&nbsp;W., Woodbrige, E.&nbsp;L., and Anderson, J.&nbsp;G.: The seasonal evolution of reactive chlorine in the northern hemisphere stratosphere, Science, 261, 1134–1136, 1993. Toon, G.&nbsp;C., Blavier, J.-F., Sen, B., Margitan, J.&nbsp;J., Webster, C.&nbsp;R., May, R.&nbsp;D., Fahey, D., Gao, R., Del Negro, L., Proffitt, M., Elkins, J.&nbsp;W., Romashkin, P.&nbsp;A., Hurst, D.&nbsp;F., Oltmans, S., Atlas, E., Schauffler, S., Flocke, F., Bui, T.&nbsp;P., Stimpfle, R.&nbsp;M., Bonne, G.&nbsp;P., Voss, P.&nbsp;B., and Cohen, R.&nbsp;C.: Comparison of MkIV balloon and ER-2 aircraft measurements of atmospheric trace gases, J.&nbsp;Geophys. Res., 104, 26779–26790, 1999. Toon, O.&nbsp;B., Browell, E., Gary, B., Lait, L., Livingston, J., Newman, P., Pueschel, R., Russell, P., Schoeberl, M., Toon, G., Traub, W., Valero, F. P.&nbsp;J., Selkirk, H., and Jordan, J.: Heterogeneous reaction probabilities, solubilities, and the physical state of cold volcanic aerosols, Science, 261, 1136–1140, 1993. Voigt, C., Schlager, H., Luo, B. P., Dörnbrack, A., Roiger, A., Stock, P., Curtius, J., Vössing, H., Borrmann, S., Davies, S., Konopka, P., Schiller, C., Shur, G., and Peter, T.: Nitric Acid Trihydrate (NAT) formation at low NAT supersaturation in Polar Stratospheric Clouds (PSCs), Atmos. Chem. Phys., 5, 1371–1380, https://doi.org/10.5194/acp-5-1371-2005, 2005. Wagner, R., Möhler, O., Saathoff, H., Stetzer, O., and Schurath, U.: Infrared spectrum of {Nitric Acid Dihydrate}: {I}nfluence of particle shape, J.&nbsp;Phys. Chem. A, 109, 2572–2581, 2005. Webster, C.&nbsp;R., May, R., Toohey, D., Avallone, L., Anderson, J., Newman, P., Lait, L., Schoeberl, M., Elkins, J., and Chan, K.: Hydrochloric acid loss and chlorine chemistry on polar stratospheric cloud particles in the {A}rctic winter, Science, 261, 1130–1134, 1993. Wegner, T., Groo{ß}, J.-U., von Hobe, M., Stroh, F., Volk, C.&nbsp;M., and Müller, R.: Chlorine activation on cold binary aerosol in Arctic spring 2004/05, Geophys. Res. Lett., to be submitted to ACP, 2010. WMO: Scientific assessment of ozone depletion: 1998, Global Ozone Research and Monitoring Project–Report No. 44, Geneva, Switzerland, 1999. WMO: Scientific assessment of ozone depletion: 2006, Global Ozone Research and Monitoring Project–Report No. 50, Geneva, Switzerland, 2007. Wolff, E.&nbsp;W. and Mulvaney, R.: Reactions on sulphuric acid aerosol and on polar stratospheric clouds in the {A}ntarctic stratosphere, Geophys. Res. Lett., 18, 1007–1010, 1991. Worsnop, D.&nbsp;R., Fox, L.&nbsp;E., Zahniser, M.&nbsp;S., and Wofsy, S.&nbsp;C.: Vapor Pressures of Solid Hydrates of {Nitric Acid}: {I}mplications for Polar Stratospheric Clouds, Science, 259, 71–74, 1993.