Ground-based observations of Arctic O3 loss during spring and summer 1997

Ground-based solar absorption spectra were measured from Fairbanks, Alaska (65-degrees N, 148-degrees W) from March to September 1997 by the Jet Propulsion Laboratory (JPL) MkIV Fourier transform infrared (FTIR) spectrometer. The derived column abundances of O-3 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 O-3 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 O-3 and HF. Data from the Halogen Occultation Experiment (HALOE) show a poleward decrease in the O-3/HF ratio at all stratospheric altitudes, so that any reductions in column O-3 due to horizontal meridional transport would have been accompanied by even larger reductions in column HF. Therefore the observed column O-3 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 O-3 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 Alesund, Spitsbergen (79-degrees N, 12-degrees E).