[en] Ozone concentrations in a power plant plume were investigated on July 20, 1977, at a plant near Lake Michigan. Measurements showed that ozone levels at first decreased and then increased significantly downwind from the stack, while the concentration of aerosol particles increased monotonically with distance from the stack. Outside the stack, sulfate aerosol and ozone concentrations increased with travel distance. To explain the chemical reaction in the plume, the authors simulated the reaction with a photokinetic model and found that the excess ozone could be explained by the excess nitrogen oxide in the plume