Partitioning between the inorganic chlorine reservoirs HCl and ClONO 2 during the Arctic winter 2005 from the ACE-FTS

From January to March 2005, the Atmospheric Chemistry Experiment high resolution Fourier transform spectrometer (ACE-FTS) on SCISAT-1 measured many of the changes occurring in the Arctic (50-80 N) lower strato- sphere under very cold winter conditions. Here we focus on the partitioning between the inorganic chlorine reservoirs HCl and ClONO2 and their activation into ClO. The simul- taneous measurement of these species by the ACE-FTS pro- vides the data needed to follow chlorine activation during the Arctic winter and the recovery of the Cl-reservoir species ClONO2 and HCl. The time evolution of HCl, ClONO2 and ClO as well as the partitioning between the two reser- voir molecules agrees well with previous observations and with our current understanding of chlorine activation during Arctic winter. The results of a chemical box model are also compared with the ACE-FTS measurements and are gener- ally consistent with the measurements.