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The Urban CO2 Dome of Essen, Germany
Reference
Henninger, S. 2008. Analysis of near surface CO2 variability within the urban area of Essen, Germany. Meteorologische Zeitschrift 17: 19-27.

What was done
Working in Germany, the author characterized the nature and determined the causes of the urban CO2 dome of the city of Essen (580,000 inhabitants living in a 210-km2 area) by means of 50 surveys made with the aid of a mobile laboratory along a 63-km route through the city over a one-year period (December 2002-November 2003), with some additional data collected in 2004 and 2005.

What was learned
Over the entire measurement period, Henninger reports that "approximately 71% of the urban carbon dioxide is affected most by the traffic density and the atmospheric stability of the urban canopy layer," while other factors "such as air temperature (9%), relative humidity (6%), the biosphere (5%), or the surface configuration (4%) have only slight impacts on the diurnal or seasonal urban CO2 pattern." With respect to the key factors of traffic and atmospheric stability, Henninger also found that "traffic density dominates the CO2 mixing ratio by day, but the near surface atmospheric stability is more important for the urban CO2 pattern by night." In this regard she additionally notes there was a linear relationship between the near-surface daytime concentrations of CO and CO2 (R2 = 0.57), which covered a CO2 range of approximately 370 to 495 ppm, but with most of the CO2 values falling below 450 ppm; while there was a similar relationship between the near-surface air's NO and CO2 concentrations (R2 = 0.69).

What it means
Of the latter two relationships, Henninger writes that "the comparison of the CO2 concentration with the air quality indicators CO and NO, which originate in combustion of vehicles, can verify the dependence of CO2 on the traffic more clearly." This work adds to growing number of studies from all around the world that come to essentially the same conclusion. See Urban CO2 Dome in our Subject Index.

Reviewed 14 May 2008