Episodios extremos de bajo contenido de ozono en la región sub-ártica de Keflavik Extreme low ozone episodes over the sub-Arctic region of Keflavik

present work presents a study of the anomalous low ozone events observed over Keflavik (Iceland) during the winter and spring months from 1992 to 2005 years. Ozone profiles from balloons sounding carried out from Keflavik were used to identify the extreme ozone events and to classify them according to different parameters. Ten days backward trajectories at different isentropic levels in the lower stratosphere have been employed to investigate the dynamical and chemical processes involved. Two types of extreme low ozone events have been found: type A, characterized by low ozone content from the tropopause up to 22 km; and type B, associated to laminated ozone structures in the lower stratosphere. Results indicate that the mechanisms re- sponsible for each type of profile vary depending on the position of the station with respect to the polar vortex.