This report presents the outcomes of the ICOS Cities project’s efforts in Zurich to develop and apply data-driven methods for the quality assurance, control, and spatial mapping of urban CO₂ using two complementary sensor networks: the mid-cost ZiCOS-M and the low-cost ZiCOS-L. These networks were deployed to support Zurich’s climate goals, including its commitment to net-zero emissions by 2040, by enabling high-resolution monitoring of CO₂ concentrations across the urban landscape.

Spatial mapping using Inverse Distance Weighting interpolation facilitated the analysis of urban CO2 variability, revealing the influence of local environmental conditions and emission sources. For both networks, data-driven methods - such as Hampel filtering for outlier removals and regular homogenization with reference instruments for drift correction - improved the data quality significantly. Together, ZiCOS-M and ZiCOS-L demonstrate a robust, multi-tiered approach to urban CO₂ monitoring.