Direct ozone depletion in springtime Antarctic lower stratospheric clouds

Abstract

It is now generally accepted that springtime Antarctic ozone depletion in the atmosphere between 17 and 22 km is related to the presence of ClO produced through heterogeneous chemistry on the surface of polar stratospheric cloud particles1,2. Below 17 km, however, where ozone depletion also occurs3, a causal link with ClO has not been established because of apparently low ClO values. Vertical motions, associated with mountain lee waves and the formation of nacreous clouds, also seemingly cannot explain observed ozone depletion4. Here we present balloon measurements of ozone and cloud particles in the lower stratosphere (10–17 km) at McMurdo Station (787° N), Antarctica, on 9 September 1988 which indicate that the cloud particles are directly involved in ozone depletion in this region. The reductions in ozone appear to be correlated with high concentrations of smaller particles, of about 0.2 micrometre radius, which dominate the surface area density in the cloud. The observations suggest a high degree of spatial inhomogeneity of free chlorine, associated with lower stratospheric clouds, and are important in understanding ozone depletion in this region.