Pertinent, previous studies of the oxidation of SO2 in the atmosphere are briefly reviewed. A project dealing with the conversion in the plume from an oil-fired power station is described in greater detail. Measurements were performed from an aircraft and included continuous registration of NOx, SO2 and ozone concentrations. The possibility of using NOx as an internal tracer is discussed; also the use of the inert tracer SF6 is treated and a special detector for the continuous registration of SF6 in relative concentrations down to 10–6 ppm is described. Preliminary results indicate a half-life for SO2 in the plume of about half an hour.