Reference
Pataki, D.E., Tyler, B.J., Peterson, R.E., Nair, A.P., Steenburgh, W.J. and Pardyjak, E.R. 2005. Can carbon dioxide be used as a tracer of urban atmospheric transport? Journal of Geophysical Research 110: 10.1029/2004JD005723.
What was done
Noting that in urban atmospheres CO2 concentrations are often elevated above those of nearby rural areas, due to the huge amounts of CO2 released to the air by the typical metropolitan region's many vehicles and numerous other large combustion sources, the authors describe what they learned from measurements of the air's CO2 concentration and its isotopic (δ13C) composition made at four locations in the Salt Lake Valley during a persistent "cold pool" event in the winter of 2004, when the air in the valley was trapped beneath an inversion that formed on 5 January and did not "mix out" until 20 days later.
What was learned
Mean daily (24-hour) CO2 concentrations at the tops of four- and five-story buildings and at the tops of 4.5- and 9-meter-tall towers ranged from 382 to 527 ppm (a 40% increase above rural background values) during the close-to-three-week measurement period. In addition, the δ13C data indicated that the major source of the cold-pool CO2 was the local combustion of gasoline and natural gas. Also, the air's CO2 concentration was generally well correlated with its particulate matter concentration.
What it means
Pataki et al. conclude that atmospheric CO2 concentrations, "which are not commonly monitored in most urban areas at present, can provide useful information regarding atmospheric transport and mixing in complex terrain such as mountain basins." In addition, their findings add to the growing body of evidence for the reality of the urban CO2 dome that is generally found over most of the world's major metropolitan complexes.