Atmos. Chem. Phys. Discuss., 10, 28687-28720, 2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). A final paper in ACP is not foreseen.
Temperature thresholds for polar stratospheric ozone loss
K. Drdla1 and R. Müller2
1NASA Ames Research Center, Moffett Field, CA, USA
2Institute for Energy and Climate Research (IEK-7), Research Centre Jülich, 52425 Jülich, Germany

Abstract. 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 HNO3 from the gas-phase. Using reaction rates on cold binary aerosol, a chlorine activation threshold temperature, TACL, is derived. At typical stratospheric conditions, TACL is similar in value to TNAT the highest temperature at which nitric acid trihydrate (NAT) can theoretically condense to form PSCs. TACL is still in use as parameterization for the threshold temperature for the onset of chlorine activation. However, perturbations can cause TACL to differ from TNAT: TACL is dependent upon H2O, potential temperature, and the sulphate aerosol loading, but unlike TNAT is not dependent upon HNO3. A parameterization of TACL is provided here, allowing it to be calculated over a comprehensive range of stratospheric conditions. Although considering TACL as a proxy for chlorine activation can be no substitute for a detailed model calculation, TACL provides a more accurate description of the temperature conditions necessary for polar ozone depletion than TNAT and can readily be used in place of TNAT.

Citation: Drdla, K. and Müller, R.: Temperature thresholds for polar stratospheric ozone loss, Atmos. Chem. Phys. Discuss., 10, 28687-28720, doi:10.5194/acpd-10-28687-2010, 2010.
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