OZONE LOSS IN THE LOWER STRATOSPHERE OVER THE UNITED-STATES IN 1992-1993 - EVIDENCE FOR HETEROGENEOUS CHEMISTRY ON THE PINATUBO AEROSOL

Ozone profiles obtained at Boulder, Colorado and Wallops Island, Virgi nia indicate that ozone was about 25% below normal during the winter a nd spring of 1992-93 in the 12-22 km region. This large ozone reductio n in the lower stratosphere, though sometimes partially compensated by higher than normal ozone above 24 km, was responsible for the low tot al column ozone values observed across the United States during this p eriod. Normal temperatures throughout the low ozone region suggest tha t transport-related effects are probably not the most important cause of the ozone deficits. The region of low ozone at Boulder corresponds closely with the location of the enhanced H2SO4/H2O aerosol from the P inatubo eruption of 1991 as measured near Boulder and at Laramie, Wyom ing. Trajectory analyses suggest that except at low altitudes in sprin g, air parcels on the days of the ozone measurements generally arrived at Boulder from higher latitude, although seldom higher than 60-degre es-N, and hence may have been subjected to heterogeneous chemical proc essing on the surface of Pinatubo aerosol droplets resulting in chlori ne-catalyzed ozone destruction, a process which is believed to be more effective under the lower winter temperatures and sunlight levels of higher latitudes.