Tropospheric ozone trends over Canada: 1980-1993

An analysis of ozone in the troposphere at five sites in Canada is presented, using ECC sonde data from 1980–1993. The entire data record has been carefully reexamined for quality, and where necessary reevaluated from the raw telemetry. Trend analysis is performed on both the raw and the corrected (normalized to the total ozone measurement) profiles. The correction factors are also examined for trends. Where required, the data are adjusted for diurnal variation introduced by changes in time of launch. We find statistically significant (2σ) decreases in concentration at all stations except Alert, and in most cases, at all levels, including the surface. The tropospheric trends we derive here are compared with corresponding lower stratospheric trends. Although the long‐term trends are similar, stratospheric variations on shorter time scales are not well‐correlated with those in the troposphere.