Flux measurements of biogenic VOCs during ECHO 2003
1Agroscope, Swiss Federal Research Station for Agroecology and Agriculture, Reckenholzstr. 191, 8046 Zürich, Switzerland
2Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, Villigen, Switzerland
3Institute of Ion Physics, University of Innsbruck, Austria
4Max Planck Institute for Chemistry, Mainz, Germany
5Research Centre Jülich, Germany
Abstract. Within the framework of the AFO 2000 project ECHO, two PTR-MS instruments were operated in combination with sonic anemometers to determine biogenic VOC fluxes from a mixed deciduous forest site in North-Western Germany using the eddy covariance (EC) technique. The measurement site was characterised by a forest of inhomogeneous composition, complex canopy structure, limited extension in certain wind directions and frequent calm wind conditions during night time. As a consequence, a considerable fraction of the measurements did not qualify for flux calculations by EC and had to be discarded. The validated results show light and temperature dependent emissions of isoprene and monoterpenes from this forest, with average emissions (normalised to 30°C and 1000 µmoles m−2 s−1 PAR) of 1.5 and 0.39 µg m−2 s−1, respectively. Emissions of methanol reached on average 0.087 µg m−2 s−1 during daytime, but fluxes were too small to be detected during night time. Upward fluxes of the isoprene oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) were also found, being two orders of magnitude lower than those of isoprene. The observed fluxes are consistent with upscalings from leaf-level emission measurements of representative tree species in this forest and, in the case of MVK and MACR, can plausibly be explained by chemical production through oxidation of isoprene within the canopy. Calculations with an analytical footprint model indicate that the observed isoprene fluxes correlate with the fraction of oaks within the footprints of the flux measurement.