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Trends in the vertical distribution of ozone are reported and compared for a number of new and recently revised data sets. The amount of ozone-depleting compounds in the stratosphere (as measured by equivalent effective stratospheric chlorine - EESC) was maximised in the second half of the 1990s. We examine the periods before and after the peak to see if any change in trend is discernible in the ozone record that might be attributable to a change in the EESC trend, though no attribution is attempted. Prior to 1998, trends in the upper stratosphere (~45 km, 4 hPa) are found to be -5 to -10% per decade at mid-latitudes and closer to -5% per decade in the tropics. No trends are found in the mid-stratosphere (28 km, 30 hPa). Negative trends are seen in the lower stratosphere at mid-latitudes in both hemispheres and in the deep tropics. However, it is hard to be categorical about the trends in the lower stratosphere for three reasons: (i) there are fewer measurements, (ii) the data quality is poorer, and (iii) the measurements in the 1990s are perturbed by aerosols from the Mt Pinatubo eruption in 1991. These findings are similar to those reported previously even though the measurements for the main satellite and groundbased records have been revised. There is no sign of a continued negative trend in the upper stratosphere since 1998: instead there is a hint of an average positive trend of ~2%per decade in mid-latitudes and ~3% per decade in the tropics. The significance of these upward trends is investigated using different assumptions of the independence of the trend estimates found from different data sets. The averaged upward trends are significant if the trends derived from various data sets are assumed to be independent (as in Pawson et al., 2014) but are generally not significant if the trends are not independent. This occurs because many of the underlying measurement records are used in more than one merged data set. At this point it is not possible to say which assumption is best. Including an estimate of the drift of the overall ozone observing system decreases the significance of the trends. The significance will become clearer as (i) more years are added to the observational record, (ii) further improvements are made to the historic ozone record (e.g. through algorithm development), and (iii) the data merging techniques are refined, particularly through a more rigorous treatment of uncertainties. [ABSTRACT FROM AUTHOR]

With the aim of improving ozonesonde observations in the upper troposphere/lower stratosphere (UTLS), we use three-dimensional forward and backward trajectories, driven by ERA-Interim wind fields to match and compare ozonesonde measurements at Payerne (Switzerland) with observations from the MOZAIC aircraft program from 1994- 2009. The uncertainties associated with the sonde-MOZAIC match technique were assessed using "self-matches", i.e. matches of instruments of the same type, such as MOZAIC- MOZAIC. Despite strong vertical gradients of ozone at the tropopause, which render the match approach difficult, the method provides excellent results, showing mean differences between different MOZAIC aircraft of ±2% (typically with a few hours between the up- and downstream match points). Matches between MOZAIC aircraft and Payerne ozonesondes show an agreement of ±5% for sondes equipped with electrochemical concentration cells (ECC) and between <5% (not scaled to total ozone) and <10% (scaled) for the Brewer-Mast (BM) sondes after 1998. Prior to 1998, BM sondes show an offset of around 20% (scaled). No break can be identified through the change from the BM to ECC sonde types in September 2002. A comparison of BM sondes with ozone measurements from the NOXAR B747 project for the period 1995-1996 show a smaller offset of around 15% (scaled), which may indicate a small drift in the MOZAIC calibration. [ABSTRACT FROM AUTHOR]