Biospheric and anthropogenic contributors to atmospheric CO₂ variability in a residential neighborhood of Phoenix, Arizona

Urban environment contributes significantly to the global carbon cycle with complex governing mechanisms due to the combined biospheric and anthropogenic contributors. In this study, we analyzed the patterns of boundary layer CO₂ flux and concentration for a residential neighborhood in Phoenix, Arizona by using the eddy covariance technique and a single column atmospheric model. Atmospheric stability, anthropogenic emission, and biogenic effect are found to be key determinants to atmospheric CO₂ variability. In a diurnal cycle, two CO₂ flux peaks coincide with morning and afternoon peak traffic hours, exemplifying the influence of traffic emissions. In the annual cycle, maximum CO₂ concentration is found in winter, mainly due to additional emission from the combustion of natural gas combined with the effect of poor dispersion. On the other hand, the minimum CO₂ concentration is found in the spring and is attributable to the strong convective mixing and active vegetation uptake. In addition, prominent hysteresis has been found between the atmospheric CO₂ concentration and air temperature with a “plait-shaped” pattern in the diurnal cycle and an “oval-shaped” loop for the seasonal variability.