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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.

Measurements of stratospheric ozone over the Northern hemisphere forthe winter/spring periods of 1997 to 2000 taken with the GOMEinstrument were used to derive the chemical ozone depletion inside thepolar vortex. GOME onboard the ERS-2 satellite measures radiationcoming from the Earth in the UV/vis spectral range.To discern the chemical depletion from dynamical influences, a modelwas developed to calculate vortex averaged diabatic descent ratesusing the radiative transfer model MIDRAD and the FURM ozoneprofiles. The permeability of the Arctic vortex was analysed by usingthe trajectory model TANGO in conjunction with a reverse domainfilling algorithm, developed within the framework of this thesis.The chemical ozone depletion at 475 K for the stratospheric coldwinter/spring period in 1997 was found to be 1.6 ppmv with a depletionrate of 22 ppbv/d for a strong, long lasting vortex until beginning ofMay. The chemical depletion of ozone in 1998, a comparingly warm year,was narrowed to a period at the end of February with 0.5 ppmv and arate of 8 ppbv/d. 1999 was quite warm and the vortex was veryinstable. A depletion of 0.3 ppmv was measured, but this is in partdue to intrusion of air from outside the vortex. 2000 was the coldestyear on record. The vortex was detected very early by GOME at the endof January. A chemical depletion of 1.8 ppmv (32 ppbv/d) until thebeginning of April was found, when the vortex broke down.

Ozone profile retrieval, ERS-2, GOME, FURM, ozone decline, Northern hemisphere. - Measurements of stratospheric ozone over the Northern hemisphere forthe winter/spring periods of 1997 to 2000 taken with the GOMEinstrument were used to derive the chemical ozone depletion inside thepolar vortex. GOME onboard the ERS-2 satellite measures radiationcoming from the Earth in the UV/vis spectral range.To discern the chemical depletion from dynamical influences, a modelwas developed to calculate vortex averaged diabatic descent ratesusing the radiative transfer model MIDRAD and the FURM ozoneprofiles. The permeability of the Arctic vortex was analysed by usingthe trajectory model TANGO in conjunction with a reverse domainfilling algorithm, developed within the framework of this thesis.The chemical ozone ..., thesis