ON THE DISTRIBUTION OF HYDROGEN-PEROXIDE IN THE LOWER TROPOSPHERE OVER THE NORTHEASTERN UNITED-STATES DURING LATE SUMMER 1988

H2O2 and NO, NO2, NO(y), O3, SO2, and H2O were measured from an aircraft over the northeastern United States in August and September 1988. The data base consists of 13 flight missions; on 14 days during different meteorological conditions, 177 vertical profiles between about 100 and 3500 m were obtained. The mixing ratio of H2O2 varied from below the detection limit of 0.2 up to 5.9 parts per billion by volume (ppbv) and it was strongly dependent on altitude, indicating that processes controlling the H2O2 occurrence in the planetary boundary layer (PBL) were different from those in the free troposphere (FT). Average H2O2 mixing ratios varied between 0.20 and 1.30 ppbv in the PBL showing, in most cases, a decrease to the ground. High H2O2 values in the PBL were observed only when NO was below 1. 5 ppbv. In more than 80% of the vertical profiles a pronounced maximum in the H2O2 mixing ratios (up to 2.3 ppbv) was observed at the top of the PBL. In the FT the H2O2 mixing ratio averaged over individual flights varied between 0.41 and 1.80 ppbv and was strongly correlated with the water vapor concentration, in agreement with a simple ''low NO(x) case'' photochemical model. The average SO2 mixing ratios were higher than the average H2O2 mixing ratios during all flights in the PBL and during most of the flights in the FT, indicating that the formation of sulfate in this region is oxidant limited for most of the time.