The C3S: Obs4MIPs format GOME-type Total Ozone Essential Climate Variable (GTO-ECV), Version 9.0 dataset was generated by combining measurements from several nadir-viewing satellite sensors (GOME/ERS-2, SCIAMACHY/Envisat, OMI/Aura, GOME-2/MetOp-A, GOME-2/MetOp-B, TROPOMI/Sentinel-5P, and GOME-2/MetOp-C) into one single cohesive record. This was done using a merging approach developed in the framework of the European Space Agency's (ESA's) Climate Change Initiative Ozone project. Firstly, the separate pixel-based level-2 observation - produced by the GOME-type Direct FITting v4 retrieval algorithm (GODFIT) are converted into level-3 products per sensor i.e. daily and monthly averages on a regular grid of 1x1 degree in latitude and longitude. Before the individual level-3 data records are finally merged into one single product, adjustments are applied in order to minimize possible inter-sensor biases and/or temporal drifts. Due to its notable long-term stability one sensor (OMI/Aura) was selected to serve as a reference for the other instruments, which are then adjusted in terms of a correction that depends on latitude and time. A detailed description of the merging approach, the generation, and the geophysical validation of GTO-ECV is provided in Coldewey-Egbers et al. (2015, 2022), Garane et al. (2018) and Lambert et al. (2022).