The potential impact of ClOx radical complexes on polar stratospheric ozone loss processes

[摘要] The importance of radical-molecule complexes for atmosphericchemistry has been discussed in recent years. In particular, theexistence of a ClO·O₂ and ClO_x water radicalcomplexes like ClO·H₂O, OClO·H₂O,OClO·(H₂O)₂, and ClOO·H₂O could play a role inenhancing the ClO dimer (Cl₂O₂) formation and therefore mayconstitute an important intermediate in polar stratospheric ozone losscycles. Model simulations performed with the Chemical Lagrangian Modelof the Stratosphere (CLaMS) will be presented to study the role ofradical complexes on polar stratospheric ozone loss processes. Themodel simulations are performed for the Arctic winter 2002/2003 at alevel of 500 K potential temperature and the results are compared toobserved ozone loss rates determined by the Match technique. Moreover,recently reported values for the equilibrium constant of the ClO dimerformation are used to restrict the number of possible model resultscaused by large uncertainties about radical complex chemistry.Ourmodel simulations show that the potential impact of ClO·O₂ onpolar ozone loss processes is small (dO₃/dt≪0.5 ppb/sunlighth) provided that the ClO·O₂ complex is only weaklystable. Assuming that the binding energies of the ClO_x watercomplexes are much higher than theoretically predicted an enhancementof the ozone loss rate by up to ≈0.5 ppb/sunlight h issimulated. Because it is unlikely that the ClO_x watercomplexes are much more stable than predicted we conclude that thesecomplexes have no impact on polar stratospheric ozone lossprocesses. Althoughlarge uncertainties about radical complexchemistry exist, our findings show that the potential impact ofClO_x radical molecule complexes on polar stratospheric ozoneloss processes is very small considering pure gas-phasechemistry. However the existence of ClO_x radical-moleculecomplexes could possibly explain discrepancies for the equilibriumconstant of the ClO dimer formation found between recent laboratoryand stratospheric measurements.

[学科分类] 大气科学