Biogenic and Anthropogenic Trace Gas Fluxes between the Atmosphere and a Polluted Mixed Forest of Central Europe

Summary

In order to investigate the exchange of trace gases above a forest canopy in the densely settled area of Frankfurt, a tower of 51 m height was erected and a constant flux model for the determination of trace gas fluxes has been developed. The reliability of the gradient model was examined under different meteorological conditions by means of two fast response systems. These investigations showed us that the constant flux assumption is fulfilled if the wind passes over the fetch. Furthermore an intercomparison between the gradient model and the eddy correlation method was performed with respect to O_3·3.

Beside ozone the concentrations of NO and NO₂ are also continuously measured and the appropriate fluxes subsequently calculated. The availability of detection methods for COS, DMS, H₂S, PAN, SO₂ and VOCs enables an application of the gradient method to be made to these species. A simultaneous measurement of all these trace gases was performed during a measuring campaign in August 1994. The goal of these efforts is to obtain information on the amount of pollutant uptake in the mixed forest ecosystem investigated for the measured species.

In order to observe the influence of air pollutants on the monitored forest, their concentration together with the meteorological parameters are compared with the CO₂ deposition. Investigations made so far seem to indicate that the daytime CO₂ uptake by the forest canopy is diminished during periods of high air pollution. An intercomparison of CO₂ fluxes measured with those calculated by a global biosphere model, which actually does not consider the influence of pollutants and biotic interferences, is accomplished at present.