The goal of this presentation is to assess our quantitative understanding of the polar stratospheric ozone loss process. We present lagrangian observations of chemical ozone loss rates and of the temporal evolution of key chlorine species during sunset. These observations allow us to derive detailed information about the kinetics of the underlying chemical processes. The results are compared with highly constrained model calculations for these air masses. The space of kinetic parameters that lead to model results reproducing the observations within combined uncertainties is explored. The consistency with laboratory measurements of the parameters is assessed. In this approach good consistency suggests a complete understanding of the chemical processes while the lack of consistency would suggest gaps in the system of reactions in the model.In particular uncertainties of the photolysis cross sections of ClOOCl have long been a limiting factor in our theoretical understanding of the rate of polar stratospheric ozone losses. While previous observationally based work suggested values slightly larger than current recommendations from the laboratory, recent laboratory work suggested values that are nearly an order of magnitude smaller than what would be required to explain the observations of ozone loss and ClO in the atmosphere. This discrepancy triggered significant new laboratory work on the photolysis cross sections of this species. We will show what the impact of these new results on our understanding of polar ozone chemistry is. We will also discuss observational constraints for any unknown ozone loss chemistry in the polar winter stratosphere.