Eighteen years of NO2 measurements using zenith-scattered sunlight are analyzed for seasonal, cyclic, and episodic variability and secular trends. The analysis shows a marked increase in stratospheric NO2 over the period, corresponding to a trend of 5% per decade, and the influences of both the El Chich¿n and Pinatubo eruptions are clearly evident. Smaller effects of the El Ni¿o-Southern Oscillation and quasi-biennial oscillation are apparent, but correlation with the solar cycle is poor after correction for autocorrelation. All of these effects are similar for sunrise and sunset NO2. ¿ 2000 American Geophysical Union