found in previous studies. The low PAN formation on 20 July, was mainly restricted by the moderate nonmethane hydrocarbon levels, whereas high PAN concentrations of 3.0 ppb on 21 July, are caused by local production in the boundary layer and by large scale advection aloft.

Abstract. The Schauinsland Ozone Precursor Experiment (SLOPE96) campaign was conducted in June 1996 to study the physicochemical transformation of pollutants and the production of photooxidants during transport from the city of Freiburg to the Schauinsland mountain. For this purpose, chemical surface measurements were made at the entrance of the valley Groges Tal, and close to the Schauinsland summit, at 1200 m altitude on a saddle at the end of the valley. In addition, measurements of ozone, NO2, and meteorological parameters were made on two tethered balloons and aboard a small aircraft. This paper describes the experimental setup and the measurements of ozone, odd-nitrogen compounds, carbonyl compounds, CO, and photolysis frequencies made during SLOPE96. The various instruments used on the different platforms were harmonized on the basis of intercomparison experiments in order to achieve a consistent picture. Large precursor concentrations from the nearby city of Freiburg are transported to Schauinsland in a valley wind system during stagnant high-pressure conditions. These conditions occurred only on 2 days of the campaign, and only 1 day (June 5) was predictable enough to allow for deployment of the aircraft and the balloons.