New observations of a large concentration of ClO in the springtime lower stratosphere over Antarctica and its implications for ozone- depleting chemistry

We have made new measurements of stratospheric chlorine monoxide (ClO) at McMurdo Station, Antarctica, during the austral spring of 1987. A peak mixing ratio of 1.6±0.4 parts per billion by volume (ppbv) (95% confidence level) was found at 19.5±1km at midday during the period September 20-24, 1987. The observed peak mixing ratio and diurnal behavior are discussed in relation to chemical depletion theories. Calculations indicate that the large observed ClO concentration provides an efficient closure for a catalytic Cl cycle through the ClO dimer mechanism, yielding good agreement with various observed features of O₃ depletion. -from Authors