Partitioning of NOy species in the summer Arctic stratosphere

Volume mixing ratio profiles of the quantitatively significant NOy species NO, NO2, HNO3, HNO4, ClNO3 and N2O5 were measured remotely from 8 to 38 km by the JPL MkIV FTIR solar absorption spectrometer during balloon flights f rom Fairbanks, Alaska (64.8 degrees N, 147.6 degrees W) on May 8 and July 8 , 1997. The observed ratio of NO, (NO+NO2) to NOy (total reactive nitrogen) is 10 to 30% greater than calculated by a steady state model using standar d photochemistry constrained by MkIV measurements of long lived precursors (e.g., H2O, CH4, CO and N2O) and SAGE II aerosol surface area. The persiste nce 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 discrepa ncy 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.