Ground based FTIR measurements of stratospheric species from Harestua, Norway during SESAME and comparison with models

Vertical columns of HF, HCl, HNO3, ClONO2, N2O, ClO and COF2 were measured at Harestua, Norway (60.22 degrees N, 10.75 degrees E, Elevation 600 a.s.l. ) beginning on 24' November 1994 and concluding on 1' May 1995 during Phase -III of the SESAME (Second European Stratospheric Arctic and Mid-latitude E xperiment) measurement campaign. The vertical columns of HCl, HNO3 and ClON O2 measured on 81 days were compared with columns calculated by the 3-D Cam bridge model SLIMCAT. In addition the results were also interpreted by comp arison with a photochemical trajectory model. Good agreement was seen for H Cl while the nitrogen compounds showed larger discrepancies, especially for ClONO2. Evidence for chlorine activation was seen with 65% reduction of th e chlorine reservoirs (HCl + ClONO2) while the levels of ClO were greatly e nhanced. Interpretation of the loss with the trajectory model indicated con densation of chlorine on PSCs. The vertical column ratio of COF2 and HF was measured to 0.21 outside the vortex and a factor of two lower inside. The recovery of ClONO2 was seen to be much faster than that of HCl in the early spring.