This document reports on the work and the results obtained in task 3.5 ‘Perform QND experiments with an advanced data assimilation system (CCFFDAS) to establish inversion strategy’. It provides a description of the CCFFDAS modelling framework, the applied QND methodology as well as the results obtained from the work performed in task 3.5 ‘Perform QND experiments with an advanced data assimilation system (CCFFDAS) to establish inversion strategy’. We have developed a prototype of a global Carbon Cycle Fossil Fuel Data Assimilation System (CCFFDAS) that combines the functionalities of the Fossil Fuel Data Assimilation System by Asefi-Najafabady et al. (2014) and of the Carbon Cycle Data Assimilation System by Kaminski et al. (2017a). The CCFFDAS was applied to assess a number of design aspects of the upcoming Monitoring and Verification Support capacity as part of the Copernicus CO2 Monitoring mission (CO2M). The assessment was based on the Quantitative Network Design technique and quantified the mission's performance in terms of the posterior uncertainty in the totals of the sectorial fossil CO2 emission rates for selected countries and the first week in June 2008. The emissions were classified into two sectors, one for electricity generation and the other for all other emissions denoted as the “other” sector. We analysed two different observing networks, ground based in situ observations and satellite based total column observations, in a range of configurations.