Nitrogen dioxide has been monitored at the International Scientific Station at the Jungfraujoch (46 ¿N, 8 ¿E) since June 1990 and at Sodankyla (67 ¿N, 27 ¿E) since January 1990. NO2 vertical column abundances are measured during the morning and evening twilights by application of the differential absorption method using the sunlight scattered at zenith in the visible range. The available time series shows a significant reduction of NO2 starting in winter 1992, after the eruption of the Mount Pinatubo volcano. A maximum decrease of about 35% is observed in January 1992 at both stations. The continued series of observations shows the recovery of the NO2 column until August 1995. These results are compared with two-dimensional chemical model calculations, including the effect of heterogeneous reactions on observed Pinatubo aerosols. In general, the modeled NO2 columns agree qualitatively with the observations although the amplitude of the seasonal variation is underestimated, possibly due to internal limitations of the model which, for example, does not include diurnal changes. The observed and calculated NO2 percent changes are in good agreement, which confirms quantitatively the impact of the heterogeneous chemistry on stratospheric NO2.¿ 1997 American Geophysical Union