Ground-based solar absorption spectra were measured from Fairbanks, Alaska (65 ¿N, 148 ¿W) from March to September 1997 by the Jet Propulsion Laboratory (JPL) MkIV Fourier transform infrared (FTIR) spectrometer. The derived column abundances of O3 declined by 35% over this period (20% in April and May, and 15% during the summer), whereas those of HF, a long-lived tracer, changed by less than 5%. High-latitude, summertime balloon observations reveal similar shapes for the volume mixing ratio profiles of O3 and HF in the lower stratosphere, where most of their column abundance resides. Vertical transport should therefore have similar effects on the column abundances of O3 and HF. Data from the Halogen Occultation Experiment (HALOE) show a poleward decrease in the O3/HF ratio at all stratospheric altitudes, so that any reductions in column O3 due to horizontal meridional transport would have been accompanied by even larger reductions in column HF. Therefore the observed column O3 decrease must be the result of chemical loss processes. Column measurements of other atmospheric gases show a summertime maximum in the NOx/NOy column ratio and little change in the chlorine partitioning. We conclude that most of the reduction in column O3 over Fairbanks from March to September 1997 was likely driven by NOx chemistry. These conclusions are supported by the similar behavior of column abundances measured by another ground-based FTIR spectrometer based in Ny ¿lesund, Spitsbergen, (79 ¿N, 12 ¿E). ¿ 1999 American Geophysical Union