Beryllium-7 as a tracer of stratospheric ozone

During a 1991 urban ozone study, simultaneous measurements of ozone and 7Be, a tracer of stratospheric air, were obtained. The purpose of the study was to evaluate the potential contribution of stratospheric air to ground-level ozone concentrations observed in Montreal, Canada during summer time. On June 27 and 28, 1991 two thunderstorms with cloud tops reaching the lower stratosphere hit the southwestern portion of the province of Quebec. High 7Be counts that were recorded indicate that stratospheric air did reach the surface in the Montreal area. By using the 7Be/ozone upper atmosphere ratio, the study concludes that, over these two days, the convective mixing of the atmosphere could have been responsible for a recorded 48 hour average 18% increase in ground-level ozone concentrations. (author) 24 refs.; 3 figs.; 4 tabs