A light and easily handled balloon-borne uv-visible spectrometer was designed for investigating ozone photochemistry in the Arctic winter. The optical sonde was flown 10 times during the EASOE campaign at Kiruna in Northern Sweden from November 1991 until March 1992. The flights gave the first simultaneous measurements of the vertical distributions of ozone and nitrogen dioxide in the Arctic winter. ¿ American Geophysical Union 1994