An important part of extra-tropical stratosphere-to-troposphere transport occurs in association with baroclinic wave breaking and cut-off decay at the tropopause. In the last decade many studies have attempted to estimate stratosphere-troposphere exchange (STE) in such synoptic events with various methods, and more recently efforts have been put on inter-comparing these methods. However, large uncertainties remain on the sensitivities to methods intrinsic parameters, and on the best measure for STE with regard to end effects on chemistry. <br><br> The goal of the present study is to address these two fundamental issues in the context of the application of a trajectory-based Lagrangian method, which has been applied in the past to climatological studies and has also been involved in inter-comparison studies, to a typical baroclinic wave breaking event. <br><br> The analysis sheds light on (i) the fine mesoscale temporal and spatial structures that are associated with episodic, rapid inflows of stratospheric air into the troposphere; (ii) the spatial resolution of 1°×1° required to reasonably capture STE fluxes in such a wave breaking event; (iii) the effective removal of spurious exchange events using a threshold residence time; (iv) the relevance of residence time distributions for capturing the effective chemical forcing of STE; (v) the large differences in the temporal evolution and geographical distribution of STE fluxes across the 2 and the 4 potential vorticity unit iso-surface definitions of the tropopause.