Partitioning of NOy species in the summer Arctic stratosphere

Volume mixing ratio profiles of the quantitatively significant NO y species NO, NO 2 , HNO 3 , HNO 4 , ClNO 3 and N 2 O 5 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 NO x (NO + NO 2 ) to NO y (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., H 2 O, CH 4 , CO and N 2 O) 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 HNO 3 on the surface of soot particles, cannot be the sole explanation. The most likely resolution to this discrepancy is that the rate of NO 2 + OH + M → HNO 3 + M (the dominant sink of NO x in the Arctic stratosphere during times of near continuous solar illumination) is significantly slower than the currently recommended rate.