Reactions of ozone and nitrogen oxides in power plant plumes

Abstract Results are presented of airborne measurements taken in the plumes of two coal and two gas-fired power plants. Measurements were made of the concentrations of NO, NO 2 , O 3 and SO 2 , temperature, relative humidity, and ultra-violet radiation. Ozone concentrations exceeding those of the surrounding ambient air were never found in these plumes, which were observed out to distances of 90 km (4 hours travel time) from the stacks. Analysis of the plume chemistry suggests that, over distances and time scales within which plumes are differentiable from background (the “near-field”), the chemistry is commonly controlled by the rates at which the plumes mix with the ambient air, rather than by chemical kinetics. Consequently, on those scales, the rates of conversion of NO to NO 2 are slow and the NO 2 /NO ratios are small (the highest ratio measured was 4.3). This analysis is consistent with the absence of observable ozone generation in the “near fields” of the power plant plumes studied.