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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
© Author(s) 2017. This work is distributed under
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Research article
27 Sep 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Harmonisation and trends of 20-years tropical tropospheric ozone data
Elpida Leventidou, Mark Weber, Kai-Uwe Eichmann, and John P. Burrows Institute of Environmental Physics (IUP), University of Bremen, Germany
Abstract. Using the convective clouds differential (CCD) method on total ozone and cloud data from three European satellite instruments GOME/ERS-2 (1995–2003), SCIAMACHY/Envisat (2002–2012), and GOME-2/MetOp-A (2007–2015) it is possible to retrieve tropical tropospheric columns of ozone (TTCO) which are in good agreement with in-situ measurements. Small differences in TTCO between the individual instruments are evident and therefore the individual datasets retrieved are harmonised into one consistent time-series starting from 1996 until 2015. Correction offsets (bias) between the instruments using SCIAMACHY as intermediate reference have been calculated and six different harmonisation scenarios have been tested. Finally, the datasets have been harmonised applying no correction to GOME data while GOME-2 has been corrected using for each grid-box the mean bias with respect SCIAMACHY for the years of common operation (2007–2012). Depending on the choice of harmonisation, the magnitude, pattern, and uncertainty of the trend can strongly vary. The harmonisation represents an additional source of uncertainty in the merged dataset and derived trend estimates. For the preferred harmonised dataset, the trend ranges between −4 and 4 DU decade-1. The trend of the tropically averaged tropospheric ozone is equal to 0 ± 0.64 DU decade-1 (2σ). Regionally, tropospheric ozone has a statistically significant increase by ~ 3 DU decade-1 over southern Africa (~ 1.5 % year-1), the southern tropical Atlantic (~ 1.5 % year-1), southeastern tropical Pacific Ocean (~ 1 % year-1), and central Oceania (~ 2 % year-1). Additionally, over central Africa (2–2.5 % year-1) and south India (~ 1.5 % year-1), tropospheric ozone increases by ~ 2 DU decade-1. These regional positive tropospheric ozone trends maybe linked to anthropogenic activities such as emissions in mega cities or biomass burning in combination with changes in meteorology or/and long range transport of precursor emissions. On the other hand, tropospheric O3 decreases by ~ −3 DU decade-1 over the Caribbean sea and parts of the North Pacific Ocean (~ −2 % year-1), and by less than −2 DU decade-1 over some regions of the southern Pacific and Indian Ocean (~ −0.5–−1 % year-1). Possible reasons for this decrease are changes in dynamical processes, convection, STE, and precipitation. The comparison of the calculated trends from the current study with tropospheric ozone trends from Heue et al. (2016) and Ebojie et al. (2016) in ten selected mega-cities showed that they agree within 2σ of the trend uncertainty.

Citation: Leventidou, E., Weber, M., Eichmann, K.-U., and Burrows, J. P.: Harmonisation and trends of 20-years tropical tropospheric ozone data, Atmos. Chem. Phys. Discuss.,, in review, 2017.
Elpida Leventidou et al.
Elpida Leventidou et al.
Elpida Leventidou et al.


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Short summary
Three individual tropical tropospheric ozone (TTCO) datasets (1996–2015) retrieved with the convective clouds differential method (Leventidou et al., 2016) have been harmonised in order to study the global and regional TTCO trends. The trends range between −4 to 4 DU/decade testing six different merging scenarios. No trend has been found for the global tropics using the preferred scenario. It is concluded that harmonisation is one of the major sources of uncertainty in the trend estimates.
Three individual tropical tropospheric ozone (TTCO) datasets (1996–2015) retrieved with the...