Mid-latitude ozone data from ER-2 aircraft measurements in 1989, 1991, and 1992 were examined to determine how sulfate aerosols from the eruption of Mt. Pinatubo had affected ozone at about 18 km. N2O was used as a tracer to help distinguish between chemical and dynamical aerosol effects. At 20--45¿N in February 1992, ozone was about 10--20% lower than February 1989 and 1991, with respect to N2O. Data from Aug. 1991--Mar. 1992 showed changes in ozone with respect to N2O, but the magnitude of those changes was not correlated with the magnitude of the changes in aerosol surface area density. ¿ American Geophysical Union 1993