Observations of stratospheric column amounts of nitrogen dioxide (NO2), nitric oxide (NO), and nitric acid (HNO3) have been made following major eruptions of the El Chich¿n and Mt. Pinatubo volcanoes. Midlatitude abundances of NO2 and NO were reduced by as much as 70% in the months following the appearance of the volcanic aerosols as compared to volcanically quiet periods. There are heterogeneous reactions which could occur on the volcanic aerosols to convert NO2 into HNO3 but no commensurate increase in HNO3 column amounts was observed at the times of NO2 decrease. ¿ American Geophysical Union 1993