Observations of stratospheric ozone at the ground level in Regina, Canada

An examination of exceptionally high ozone values (138–228 ppb) recorded at the ground level in Regina, Saskatchewan suggested that they were due to downward transport from the stratosphere. The occurrence of high O3 concentrations, in excess of 120 ppb near the ground, due to stratospheric intrusion appears to be an uncommon local phenomenon even with the frequent passages of upper troughs and the prevalence of jet streams, etc. Characteristically, such O3 episodes are observed to last only 1–3 h.