Results are presented of airborne measurements taken in oil sands extraction plant plumes in Fort McMurray, Alberta, Canada. Measurements with fast response monitors at a high sampling rate illustrate the narrow reaction zone in the plume caused by a turbulent diffusion reaction of NO to NO2 as suggested by theoretical and laboratory studies. The measured conversion rates of NO to NO2 varied considerably from day to day, from 0.2 to 21.4% min−. Analysis of the oxidation rate of NO to NO2 and of the atmospheric turbulence parameter reveals that, over the distances and time scales within which the plumes are distinguishable from the background, the nitrogen oxides chemistry in the plumes is controlled by the rates at which the plumes mix with the ambient air (containing ozone), rather than by chemical kinetics.