M. von Hobe, et al.
Evidence for heterogeneous chlorine activation in the tropical UTLS
Atmospheric Chemistry and Physics, 11(1), 241-256, 2011; doi: 10.5194/acp-11-241-2011
O3 18OO2 O18OO O17OO HCl


Airborne in-situ observations of ClO in the tropics were made during the TROCCINOX (Aracatuba, Brazil, February 2005) and SCOUT-O3 (Darwin, Australia, November/December 2005) field campaigns. While during most flights significant amounts of ClO (≈10–20 parts per trillion, ppt) were present only in aged stratospheric air, instances of enhanced ClO mixing ratios of up to 40 ppt – significantly exceeding those expected from gas phase chemistry – were observed in air masses of a more tropospheric character. Most of these observations are associated with low temperatures or with the presence of cirrus clouds (often both), suggesting that cirrus ice particles and/or liquid aerosol at low temperatures may promote significant heterogeneous chlorine activation in the tropical upper troposphere lower stratosphere (UTLS). In two case studies, particularly high levels of ClO observed were reproduced by chemistry simulations only under the assumption that significant denoxification had occurred in the observed air. However, to reproduce the ClO observations in these simulations, O3 mixing ratios higher than observed had to be assumed, and at least for one of these flights, a significant denoxification is in contrast to the observed NO levels, suggesting that the coupling of chlorine and nitrogen compounds in the tropical UTLS may not be completely understood.


  author = "M. von Hobe and J.-U. Grooß and G. Günther and P. Konopka and I. Gensch and M. Krämer and N. Spelten and A. Afchine and C. Schiller and A. Ulanovsky and N. Sitnikov and G. Shur and V. Yushkov and F. Ravegnani and F. Cairo and A. Roiger and C. Voigt and H. Schlager and R. Weigel and W. Frey and S. Borrmann and R. Müller and F. Stroh",
  title = "Evidence for heterogeneous chlorine activation in the tropical UTLS",
  year = 2011,
  journal = "Atmospheric Chemistry and Physics",
  volume = 11,
  number = 1,
  pages = "241-256",
  month = "Jan",
  keywords = "O3, 18OO2, O18OO, O17OO, HCl",
  doi = "10.5194/acp-11-241-2011",
  url = ""
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