Within the Mesoscale Alpine Programme MAP, the Rhine valley ozone study ROM was conducted, putting additional instrumentation in the area just south of the Lake of Constance. The vertical structure and the temporal evolution of the planetary boundary layer (PBL) and the ozone concentrations during foehn episodes were observed by using a tethersonde system carrying up to three meteorological and up to two ozone sondes simultaneously, a sonde mounted on the Pfaender cable car, a sodar as well as an ultrasonic anemometer and one conventional ground-based meteorological station. A wind-temperature radar (WTR) was operated near Rankweil, about 20 kin south. The potential of the primarily vertical sounding devices, especially of the new tethered balloon system and the cable car sonde, to detect in detail the complex meteorological and ozone structure of the boundary layer is demonstrated for the strong foehn case on 24 October 1999. The data set highlights a lot of interesting features like the often occurring lifting of the foehn flow above a prevailing cold air pool when propagating out of the Rhine valley into the Alpine foreland, giving rise to strong vertical gradients of ozone, temperature and humidity as well as pronounced vertical wind shear. The WTR gives insight how far south the near-surface cold air pool may reach during foehn.