THE POTENTIAL INFLUENCE OF CLO-CENTER-DOT-O-2 ON STRATOSPHERIC OZONE DEPLETION CHEMISTRY

The inability to explain the observed oxygen suppression of chlorine p hotosensitized ozone loss remains a gap in our understanding of the ph otochemistry responsible for depletion of the stratospheric ozone laye r. It has been suggested that the presence of a weakly bound ClO . O-2 complex could explain this effect. The existence of this complex woul d alter the chlorine budget of the stratosphere, perhaps reducing the chlorine available for catalytic ozone destruction, On the other hand, the chemistry of ClO . O-2 provides two new pathways for ClO dimer fo rmation, which could increase the rate of catalytic ozone loss. In thi s paper, we constrain the kinetic rate system of ClO . O-2 to match th e measured Cl-y budget. It is shown that ClO . O-2 cannot be both fair ly stable and rapidly form the ClO dimer, or the resulting partitionin g of chlorine becomes incompatible with observations of both ClO and t otal available chlorine. These constraints allow that either: (1) the ClO . O-2 is fairly stable, but does not significantly enhance ClO dim er formation and therefore has a negligible effect on ozone loss rates , or (2) the ClO . O-2 complex is only very weakly stable, but does ra pidly form the ClO dimer, and therefore can influence stratospheric oz one depletion. Even at the ClO . O-2 mixing ratios allowed under the a ssumption of weak stability, 0.1 to 0.2 ppbv, significant ozone loss r ate enhancements were calculated. Of course, the chlorine budget const raint also allows for a third possibility; that ClO . O-2 is neither v ery stable nor forms Cl2O2 very rapidly. Measured limits on the reacti on rates for ClO . O-2 to form the ClO dimer would greatly aid the res olution of this issue. Since the uncertainties about ClO . O-2 chemist ry are so large, a potential role for ClO . O-2 in stratospheric ozone loss cannot be ruled out at this time.