Carbon dioxide fluxes over an urban park area

From September 2006 to October 2007 turbulent fluxes of carbon dioxide were measured at an urban tower station (26 m above ground level, z/zh = 1.73) in Essen, Germany, using the eddy covariance technique. The site was located at the border between a public park area (70 ha) in the south–west of the station and suburban/urban residential as well as light commercial areas in the north and east of the tower. Depending on the land-use two different sectors (park and urban) were identified showing distinct differences in the temporal evolution of the surface-atmosphere exchange of CO2. While urban fluxes appear to be governed by anthropogenic emissions from domestic heating and traffic (average flux 9.3 μmol m−2 s−1), the exchange of CO2 was steered by biological processes when the park contributed to the flux footprint. The diurnal course during the vegetation period exhibited negative daytime fluxes up to −10 μmol m−2 s−1 on average in summer. Nevertheless, with a mean of 0.8 μmol m−2 s−1 park sector fluxes were slightly positive, thus no net carbon uptake by the surface occurred throughout the year. er to sum the transport of CO2 a gap-filling procedure was performed by means of artificial neural network generalisation. Using additional meteorological inputs the daily exchange of CO2 was reproduced using radial basis function networks (RBF). The resulting yearly sum of 6031 g m−2 a−1 indicates the entire study site to be a considerable source of CO2.