Untersuchungen zum Gasaustausch - Entwicklung und Applikation eines zeitlich aufgelösten Massenbilanzverfahrens

The study presents a novel technique for measuring time resolved gas transfer rates at the water surface. By applying this new mass balance technique neither absolute concentrations of the trace gases nor the measurement of their concentrations in the water phase is required. Gas fluxes are calculated exclusively by the temporal change of the air-sided concentrations in an evasion experiment. The high temporal resolution of this procedure allows fast measurements under different conditions. Systematic measurements of gas exchange rates are now feasible within hours. By using UV-spectroscopy, simultaneous concentration measurements of volatile aromatics in the air and water phases verified the results obtained by the presented technique. Within the framework of the UV-measurements a method was developed to determine the air-sided concentrations of the aromatics precisely, even at low spectral resolution of the spectrometer. The differential optical absorption spectroscopy was successfully applied to a wide concentration range of these tracers. Reliable gas transfer velocities are now also available for very low wind speeds and friction velocities. The transition of the Schmidt number exponent from a flat to a rough water surface was reproduced. The transition begins at unexpectedly low wind speeds and extends over a wide range of wind speeds. For the first time the effect of chemically enhanced gas-exchange was demonstrated under a variety of chemical and physical conditions.