The Schauinsland Ozone Precursor Experiment (SLOPE) was conducted in June 1996 as part of the former European Experiment on Transport and Transformation of Environmentally Relevant Trace Constituents in the Troposphere Over Europe (EUROTRAC) subproject Tropospheric Ozone Research (TOR) in order to study the photochemical formation of ozone and the degradation of the precursors in the plume of the city of Freiburg on its way to Schauinsland. Chemical and meteorological measurements were made at several surface sites in a valley that channels the airflow to Schauinsland, including vertical profiles at several locations, and aboard a small aircraft. A tracer experiment with SF6 was made in order to establish transport and dispersion in the valley. Particular emphasis was on the determination of the OH concentration from the decay of hydrocarbons during transport. The relatively high OH concentration of 7¿106 cm-3 in the presence of high NOx concentrations (3--15 ppb) indicates the potential for unidentified processes in the HOx budget in the high-NOx regime which may have important consequences for the ozone budget and smog chemistry in the urban/suburban environment. ¿ 2000 American Geophysical Union