Ozone balloon soundings at Payerne (Switzerland): Reevaluation of the time series 1967–2002 and trend analysis

Abstract

This study documents the history of the Payerne (Switzerland) ozone series obtained with the Brewer‐Mast sonde from the end of 1966 until the change to the electrochemical concentration cell (ECC) sonde in autumn 2002, as well as the reevaluation of the original data. Several corrections were made in order to improve the homogeneity and the quality of the time series. We furthermore derived long‐term trends for the reevaluated time series using atmospheric variables in a stepwise regression model. In the stratosphere, trends over the 1970–2002 period remain nearly the same as over periods ending a few years earlier. For tropospheric ozone trends, a hockey stick model allowing for a change in trend in 1990 was used and a sensitivity analysis with different data sets was carried out. Besides the standard World Meteorological Organization (WMO) data evaluation procedure, we used alternative data sets (1) accounting for the preflight laboratory calibrations, or (2) ignoring the total ozone normalization, (3) as well as correcting for chemical interference with SO2. With all data sets, tropospheric trends were strongly positive in all seasons over the 1967–1989 period. In the 1990–2002 period, winter trends remained positive over the whole troposphere with all data sets, whereas in the other seasons, trends were generally negative near the ground and shifted to zero or positive values with increasing altitude in the troposphere. The alternative evaluation procedures strongly affect the derived tropospheric trends in the 1990–2002 period and their uncertainties.