What was learned
The highest CO2 concentrations, occasionally exceeding 500 ppm, were recorded during wintertime inversions, with the downtown site showing the highest CO2 concentrations at night, but exhibiting similar values to the neighborhood site in the daytime, while the rural site, according to the four researchers, "showed consistently lower and relatively constant values." This pattern was also observed in the summer, although they found that "absolute CO2 concentrations were lower at all three sites, particularly during afternoon, well-mixed atmospheric conditions." In addition, they report that the "inverse analysis of CO2 sources and the O isotope composition of ecosystem respiration showed large contributions (>50%) of natural gas combustion to atmospheric CO2 in the wintertime, particularly at the city center, and large contributions (>60%) of biogenic respiration to atmospheric CO2 during the growing season, particularly at the rural site."
What it means
Pataki et al. say their results "illustrate that spatial and temporal patterns of urban CO2 concentrations and isotopic composition can be used to infer patterns of energy use by urban residents as well as plant and soil processes in urban areas," concluding that "these measurements have great potential for inferring patterns of human activities and biological respiration in complex, human-dominated ecosystems."
Reviewed 1 August 2007
Pataki, D.E., Xu, T., Luo, Y.Q. and Ehleringer, J.R. 2007. Inferring biogenic and anthropogenic carbon dioxide sources across an urban to rural gradient. Oecologia 152: 307-322.