GROUND-BASED FTIR MEASUREMENTS OF STRATOSPHERIC TRACE SPECIES FROM ABERDEEN DURING WINTER AND SPRING 1993 94 AND 1994/95 AND COMPARISON WITH A 3D MODEL/

Vertical column abundances of HCl, ClONO2, HF and HNO3 have been obtai ned from infrared solar absorption measurements made at Aberdeen, UK ( 57 degrees N, 2 degrees W) during the periods January 13 1994 - May 8 1994 and November 23 1994.- April 19 1995. The measurements reveal the partitioning of inorganic chlorine (Cl-y) inside and outside the pola r vortex during these two winter and spring periods. Stratospheric tem peratures within the northern polar vortex during 1993/94 were not col d throughout January and most of February. The measurements reported h ere suggest that following a brief period of chlorine activation in la te February and early March, the active chlorine within the vortex rec overed rapidly to form ClONO2 resulting in in-vortex ClONO2 columns of 7 x 10(15) molecules cm(-2). In contrast, measurements during January 1995 suggest extensive in-vortex activation with in-vortex HCl + ClON O2 as low as 3.6x10(15) molecules cm-2. High day-to-day variability in the ClONO2 columns observed during February is evidence for the trans port of ClONO2 rich air from high to mid latitudes during the late win ter. The implications for mid latitude O-3 loss are discussed. A preli minary comparison of the HCl, ClONO2, and HNO3 column data from winter 94/95 with a three-dimensional chemical transport model shows that th e model generally reproduces well the day-to-day variability and absol ute magnitude of the observed columns, especially for HNO3 outside of the vortex.