COMPOSITION MEASUREMENTS OF THE 1989 ARCTIC WINTER STRATOSPHERE BY AIRBORNE INFRARED SOLAR ABSORPTION-SPECTROSCOPY

Simultaneous measurements of the stratospheric burdens of H2O, HDO, OCS, CO2, O3, N2O, CO, CH4, CF2Cl2, CFCl3, CHF2Cl, C2H6, HCN, NO, NO,, HNO3, ClNO3, HOCl, HCl, and HF were made by the Jet Propulsion Laboratory MkIV interferometer on board the NASA DC-8 aircraft during January and early February 1989 as part of the Airborne Arctic Stratosphere Experiment (AASE). Data were acquired on 11 flights at altitudes of up to 12 km over a geographic region covering the NE Atlantic Ocean, Iceland, and Greenland. Analyses of the chemically active gases reveal highly perturbed conditions within the vortex. The ClNO3 abundance was chemically enhanced near the edge of the vortex but was then depleted inside. HCI was chemically depleted near the vortex edge and became even more depleted inside. In fact, by late January deep inside the vortex, HCI was either completely removed up to 27-km altitude, or partially removed to an even greater altitude. NO2 was also severely depleted inside the vortex. In contrast to Antarctica, H2O and HNO3 were both more abundant inside the vortex than outside. While for H2O this is solely a consequence of descent (without accompanying dehydration), HNO3 additionally shows evidence for chemical enhancement inside the vortex. One exception to the high HNO3 abundances inside the vortex occurred on January 31 when stratospheric temperatures above the aircraft fell below 190 K. However, following this event, HNO3 burdens fully recovered, suggesting that if the loss on January 31 was due to temporary freeze-out of HNO3, the resulting particles reevaporated above 12 km. Taken together, these results suggest that although the Arctic vortex did not get cold enough to produce any dehydration, nor as vertically extensive denitrification as occurred in Antarctica, nevertheless, enough heterogeneous chemistry still occurred to convert over 90% of the inorganic chlorine to active forms in the 14- to 27-km altitude range by early February 1989.