The polar vortex is a unique airmass existing in the winter pole's stratosphere. Sometimes the polar vortex will go on 'excursions' and extend down to mid-latitudes. And sometimes the polar vortex will stay centered on the pole, but filaments will detach and extend down to mid-latitudes. When either of these 'intrusion' events occur, the unique stratospheric air of the pole temporarily affects the mid-latitude environment.

I will present a few polar intrusion events that occurred over Toronto that were identified using the time series of HCl and HF measured at the Toronto Atmospheric Observatory (TAO). Maps of potential vorticity are also used to confirm the polar intrusion events.