Direct quantification of greenhouse gas emissions in a mid-sized German city

Urban areas account for approximately two-thirds of global anthropogenic carbon dioxide (CO₂) emissions. Direct greenhouse gas flux measurements provide the basis for quantifying city emissions and developing effective mitigation strategies. Eddy covariance (EC) is a direct, continuous monitoring method for capturing net surface fluxes of CO₂ (and other greenhouse gases) at a high temporal resolution (30 min). Despite the methodological potential, only a few urban locations worldwide currently estimate greenhouse gas fluxes with the EC method.

In this study we established two EC systems in the city of Münster in northwest Germany. Münster is a midsized city (about 300,000 in habitants), known for its extensive cycling culture and green urban character. Often called the bicycle capital of Germany, Münster combines urban life with abundant parks, green spaces, and a high modal share of bicycle traffic. Since May 2025, continuous 30-min observations of CO₂ and energy fluxes are being collected in two locations, combining a rooftop (33m above the ground) EC system sampling a heterogeneous urban footprint with complementary near-surface (2.4m above the ground) measurements over unmanaged urban grassland and impervious surfaces. This coordinated observational design enables investigation of how different urban surface types contribute to the integrated city-scale CO₂ exchange and provides a robust basis for long-term carbon-cycle monitoring.

In addition, the observational framework is complemented by process-based urban land-surface modeling using the Surface Urban Energy and Water Balance Scheme (SUEWS), which enables a bottom-up representation of urban energy and CO₂ exchange. In combination with the multi-site EC measurements, SUEWS will support interpretation of seasonal and diurnal variability and provide a first-order partitioning of biogenic and anthropogenic contributions at the neighborhood scale.