Measurements of reactive nitrogen gases (NO, NO2, NOy), as well as related chemical (O3, CO, aerosol black carbon, radon, selected nonmethane hydrocarbons) and meteorological parameters were made on board the R/V Malcolm Baldridge prior to and subsequent to the 1992 ASTEX (Atlantic Stratocumulus Transition Experiment) in the North Atlantic Ocean during June and July 1992. Results showed indications of well-defined plumes from North America and Europe from both chemistry and back trajectory data. Elevated ozone concentrations were also observed in airmasses from uninhabited continental regions. Chemical and meteorological data were incorporated into a simple photochemical model in which ozone destruction predominated over generation. The principal reaction leading to ozone destruction was O(1D) + H2O → 2OH.