Modeling carbon dioxide exchange in a single-layer urban canopy model

Carbon dioxide (CO₂) is the primary greenhouse gas that drives the global climate change in past centuries. Much effort of carbon mitigation as a countermeasure to global changes has focused on the urban areas – the hotspots of fossil fuel and concentrated emission and pollutants. Despite their critical role in CO₂ exchange in urban ecosystem, emission from vegetation and soils are largely overlooked in existing urban land surface models. In this study, we parameterized the biogenic CO₂ exchange in cities using an advanced single-layer urban canopy model, by incorporating plant physiological functions in the built environment. In addition, the proposed model also includes the anthropogenic CO₂ fluxes especially that from traffic emissions based on gridded dataset. We evaluate the proposed model using field measurements from an eddy covariance flux tower located at west Phoenix, Arizona, USA. The model results are in good agreement with the observed carbon flux over the built terrain, with a root mean squared error of 0.21 mg m⁻²s⁻¹. Furthermore, our simulations show that the abiotic traffic-emitted CO₂ amounts the largest source in cities, as expected. Nevertheless, the biogenic carbon exchange can be significantly enhanced in the built environment, making an equally important contributor to the total carbon emission especially in sub-urban areas.