DOAS and scintillation anemometry for the determination of trace gas fluxes and budgets

A simple layout for a DOAS system based on a commercially available spectrometer with CCD-detector is presented. The open-path light beam over several kilometers is controlled automatically to maintain an optimal beam alignment. The DOAS system is operated in parallel with a scintillation anemometer (scidar), which optically measures the path averaged crosswind. This arrangement provides fluxes of atmospheric constituents under the constraint of homogeneous concentrations along the light paths. In the framework of the EU-project ''VOTALP'' (''vertical ozone transport in the Alps'') 5 combined systems were used to evaluate the budget of NO2, O-3, formaldehyde, toluene and SO2 fluxes in the Mesolcina valley in Switzerland. Two scidar/DOAS systems were set up in different heights across the northern end of the valley, two across the southern end and one parallel to the valley sidewall. Beam lengths ranged from 0.6 to 2.7 km. Results of the flux measurements are presented.