Urban greenhouse gas monitoring across the Barcelona Metropolitan Area

An urban greenhouse gas (GHG) monitoring network has been established in the Barcelona Metropolitan Area to support the evaluation of GHG mitigation strategies. The network currently consists of five measurement sites equipped with high-precision Picarro analysers providing continuous observations of carbon dioxide (CO₂) and methane (CH₄). These measurements, in combination with atmospheric modelling will be used to investigate spatial and temporal variability in urban GHG concentrations.

The five sites (Fabra, ICM, ICTA, IDAEA, and UPC-Agropolis) were strategically selected to represent a range of urban and peri-urban environments, including a natural forest, an urban coastal site, a traffic-influenced highway location on the outskirts of the city, an urban park embedded within a densely built area, and a peri-urban agricultural region. This configuration enables the assessment of how different landuse types and emission sources influence observed GHG mole fractions across the metropolitan area.

Hourly averaged CO₂ mole fractions show pronounced differences between sites. Lower values are observed at the forested Fabra site, while the ICTA site, located near a major highway, exhibits the highest mole fractions and the largest variability. These spatial contrasts are consistent with results from previous multi-site measurement campaigns in Barcelona, which indicated that densely urbanized, impermeable landscapes are associated with enhanced CO₂ concentrations compared to greener areas, particularly during morning hours dominated by traffic emissions.

Maintaining a continuous urban monitoring network is essential for capturing both spatial and temporal variability in GHG concentrations and for improving our understanding of urban atmospheric processes. Such observations are also critical for constraining and validating atmospheric models and for quantifying changes in emissions over time. Here, we present recent observations from the Barcelona Metropolitan Area GHG network and illustrate their application to the study of greenhouse gas variability in complex urban environments.