Abstract
Abstract. The ozonesonde stations at Uccle (Belgium) and De Bilt (the Netherlands) are separated by only 175 km but use different ozonesonde types (or different manufacturers for the same electrochemical concentration cell (ECC) type), operating procedures, and correction strategies. As such, these stations form a unique test bed for the Ozonesonde Data Quality Assessment (O3S-DQA) activity, which aims at providing a revised, homogeneous, consistent dataset with an altitude-dependent estimated uncertainty for each revised profile. For the ECC ozonesondes at Uccle mean relative uncertainties in the 4–6 % range are obtained. To study the impact of the corrections on the ozone profiles and trends, we compared the Uccle and De Bilt average ozone profiles and vertical ozone trends, calculated from the operational corrections at both stations and the O3S-DQA corrected profiles. In the common ECC 1997–2014 period, the O3S-DQA corrections effectively reduce the differences between the Uccle and De Bilt ozone partial pressure values with respect to the operational corrections only for the stratospheric layers below the ozone maximum. The upper-stratospheric ozone measurements at both sites are substantially different, regardless of the correction methodology used. The origin of this difference is not clear. The discrepancies in the tropospheric ozone concentrations between both sites can be ascribed to the problematic background measurement and correction at De Bilt, especially in the period before November 1998. The Uccle operational correction method, applicable to both ozonesonde types used, diminishes the relative stratospheric ozone differences of the Brewer–Mast sondes in the 1993–1996 period with De Bilt to less than 5 % and to less than 6 % in the free troposphere for the De Bilt operational corrections. Despite their large impact on the average ozone profiles, the different (sensible) correction strategies do not change the ozone trends significantly, usually only within their statistical uncertainty due to atmospheric noise. The O3S-DQA corrections bring the Uccle and De Bilt ozone trend estimates for 1997–2014 closer to each other in the lower stratosphere and lower troposphere. Throughout the whole vertical profile, these trend estimates are, however, not significantly different from each other, and only in the troposphere significantly positive. For the entire Uccle observation period (1969–2014), the operational corrections lead to height-independent and consistent ozone trends for both the troposphere and the stratosphere, with rates of +2 to +3 % decade−1 and −1 to −2 % decade−1, respectively.
Highlights
It is a minor constituent, ozone is present throughout the whole lower atmosphere
Because typical horizontal ozone correlation lengths are generally much longer than the distance between both stations, except in the boundary layer, and because the time separation between the launches at those stations is at most 1 day, the comparisons of the average profiles and trends should enable us to investigate the impact of the correction strategies on the ozone profiles and resulting trends
In Uccle, where the time series is built up with both BM and electrochemical concentration cell (ECC) ozonesondes, the main feature of the operational PRESTO correction is the combination of a pressure and temperature-dependent pump efficiency correction with the total ozone normalisation
Summary
It is a minor constituent, ozone is present throughout the whole lower atmosphere. Since ozone at different (vertical) atmospheric layers is formed and destroyed by different photochemical reactions – and with precursor emissions from both natural and anthropogenic sources – the time variability of the ozone abundance (on seasonal, interannual, and decadal timescales) highly depends on the location (height) of ozone molecules in the atmosphere This is illustrated, in which stratospheric, tropospheric, and boundary layer ozone monthly means are shown for the period 1969–2014 for the Uccle (Brussels, Belgium) station and for the period 1993–2014 for De Bilt (the Netherlands). Uccle and De Bilt have a similar vertical distribution of ozone (see Van Malderen et al, 2014, and Fig. 1), with similar average annual cycles for especially stratospheric and free tropospheric ozone (see Fig. 2), geophysical differences between the two sites cannot completely ruled out As a consequence, these data should enable us to investigate the impact of different correction strategies on the vertical ozone profiles and the derived trends. The BM sondes flown operationally at Hohenpeissenberg, Payerne, and Uccle from 1994 to 1997 overestimate O3 by up to 25 % in the upper troposphere compared to the MOZAIC aircraft measurements (Staufer et al, 2014)
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