Volume mixing ratio profiles of the quantitatively significant NOy species NO, NO2, HNO3, HNO4, CINO3 and N2O5 were measured remotely from 8 to 38 km by the JPL MkIV FTIR solar absorption spectrometer during balloon flights from Fairbanks, Alaska (64.8¿N, 147.6¿W) on May 8 and July 8, 1997. The observed ratio of NOx (NO+NO2) to NOy (total reactive nitrogen) is 10 to 30% greater than calculated by a steady state model using standard photochemistry constrained by MkIV measurements of long lived precursors (e.g., H2O, CH4, CO and N2O) and SAGE II aerosol surface area. The persistence of this discrepancy to 38 km altitude suggests that processes involving aerosols, such as the reduction of HNO3 on the surface of soot particles, cannot be the sole explanation. The most likely resolution to this discrepancy is that the rate of NO2+OH+M→HNO3+M (the dominant sink of NOx in the Arctic stratosphere during times of near continuous solar illumination) is significantly slower than the currently recommended rate. ¿ 1999 American Geophysical Union