Dt. Shindell, THE POTENTIAL INFLUENCE OF CLO-CENTER-DOT-O-2 ON STRATOSPHERIC OZONE DEPLETION CHEMISTRY, Journal of atmospheric chemistry, 26(3), 1997, pp. 323-335
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.