Redistribution of reactive odd nitrogen in the lower Arctic stratosphere

In‐situ measurements of total reactive odd nitrogen (NOy) were made from the NASA DC‐8 aircraft in the lower arctic stratosphere during the 1989 Airborne Arctic Stratospheric Expedition. Throughout January and February, NOy mixing ratios were typically between 0.5 and 3 parts per billion by volume (ppbv) at altitudes between 10 and 12.5 km. During several flights late in the mission, events of unusually high NOy occurred with mixing ratios up to 12 ppbv at these altitudes. Simultaneous measurements of N2O, O3, and H2O during these events suggest that large changes in NOy are not expected. The elevated NOy values are interpreted as a vertical redistribution of NOy in the lower stratosphere resulting from gravitational sedimentation of aerosol particles containing HNO3. No evidence of the redistribution of H2O is noted consistent with observations of denitrification without dehydration higher in the stratosphere.