BERYLLIUM-7 AS A TRACER OF STRATOSPHERIC OZONE - A CASE-STUDY

During a 1991 urban ozone study, simultaneous measurements of ozone an d Be-7, a tracer of stratospheric air, were obtained. The purpose of t he study was to evaluate the potential contribution of stratospheric a ir to ground-level ozone concentrations observed in Montreal, Canada d uring the summer time. On June 27 and 28, 1991 two thunderstorms with cloud tops reaching the lower stratosphere hit the southwestern portio n of the province of Quebec. High Be-7 counts that were recorded indic ate that stratospheric air did reach the surface in the Montreal area. By using the Be-7/ozone upper atmosphere ratio, the study concludes t hat, over these two days, the convective mixing of the atmosphere coul d have been responsible for a recorded 48 hour average 18% increase in ground-level ozone concentrations.