OZONE AND HYDROGEN-PEROXIDE DURING SUMMER SMOG EPISODES OVER THE SWISS PLATEAU - MEASUREMENTS AND MODEL SIMULATIONS

As part of the POLLUMET (Pollution and Meteorology in Switzerland) stu dy, measurements of O-3, NO2, and H2O2 were made at ground stations, b y aircraft, and manned hydrogen balloons to characterize the photochem ical processes prevailing during times of high ozone production. Durin g summer smog episodes, elevated ozone concentrations were found over the whole area of the Swiss Plateau, which is a densely populated and industrialized region. However, NO2 concentrations were generally at a low level in the afternoon. An increase of hydrogen peroxide concentr ation in the mixing layer during photochemical episodes was observed. To understand better the photochemical processes which control ozone f ormation over the Swiss Plateau, calculations with the Harvard photoch emical model and the Harwell photochemical trajectory model were condu cted. A comparison of model results with measurements of the triad O-3 , NO2, and H2O2 indicates an ozone formation under low NOx conditions.