Ozone budget for Sable Island derived from the Aura/OMI satellite and from ozonesonde vertical profiles during IONS 2004 (left) and 2006 (right), differentiating contributions from the boundary layer (purple), Regional and convective sources (red), Stratospheric intrusions (yellow), and advected ozone (blue). These budgets show that O3 from stratospheric intrusions contribute significantly to the total tropospheric O3. [Figure Anne Thompson, Penn State University]