Carbon dioxide fluxes over an urban park area

Abstract From September 2006 to October 2007 turbulent fluxes of carbon dioxide were measured at an urban tower station (26 m above ground level, z/z h  = 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 CO 2 . 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 CO 2 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. In order to sum the transport of CO 2 a gap-filling procedure was performed by means of artificial neural network generalisation. Using additional meteorological inputs the daily exchange of CO 2 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 CO 2 .