Ozone loss by the HOCl catalytic cycle: do models have it right?

The HOCl catalytic cycle for ozone loss is important in the mid-latitude stratosphere. We use a diurnal steady- state photochemical model to calculate profiles of HOCl for conditions sampled by two high-altitude balloon- borne instruments, MkIV and FIRS-2. To assess how well this model represents ozone loss by the HOCl cycle, we compare our calculations of HOCl and its precursors, ClO and HO2, with measurements obtained by an FTIR solar absorption spectrometer (MkIV), a far-infrared emission spectrometer (FIRS-2), a submillimeterwave limb sounder (SLS), and a microwave limb sounder (MLS on the Aura satellite). We then evaluate these comparisons in light of a number of recent laboratory studies of the main formation mechanism of HOCl, the reaction of ClO + HO2. Preliminary comparisons between model and observations suggest better agreement might be achieved with a faster rate constant.