Gas phase H2O2 was measured in surface air on the NOAA ship Malcolm Baldrige from June 8 to 27, 1992 (Julian days 160–179), during the Atlantic Stratocumulus Transition Experiment/Marine Aerosol and Gas Exchange experiment in the eastern subtropical North Atlantic region. Average H2O2 mixing ratios observed were 0.63±0.28 ppbv, ranging between detection limit and 1.5 ppbv. For the entire experiment, only weak or no correlation was found between H2O2 mixing ratio and meteorological parameters (pressure, temperature, humidity, or UV radiation flux) as well as with tracers of continental air masses (CO, black carbon, radon). The average daily H2O2 cycle for the entire period exhibits a maximum of 0.8±0.3 ppbv near sunset and a minimum of 0.4±0.2 ppbv 4–5 hours after sunrise. Several clear H2O2 diurnal variations have been observed, from which a first‐order removal rate of about 1×10−5 s−1 for H2O2 can be inferred from nighttime measurements. This rate compares well with those deduced from measurements taken at Cape Grim (Tasmania, 41°S) and during the Soviet‐American Gas and Aerosol III experiment (equatorial Pacific Ocean).
