Transport of ozone and pollutants from North America to the North AtlanticOcean during the 1996 Atmosphere/Ocean Chemistry Experiment (AEROCE) intensive

Research flights were conducted to investigate the episodic occurrence of e nhanced ozone mixing ratios over the North Atlantic Ocean (NAO) during the spring as part of the Atmosphere/Ocean Chemistry Experiment(AEROCE). We mea sured meteorological variables, trace gases, and aerosol light scattering f rom the University of Wyoming King Air research aircraft during 16 research flights in April and early May 1996. The flights were conducted over easte rn North America and over the NAO between the United States and Bermuda. On April 28, a cold front was located just west of Bermuda while a second sys tem developed over the Midwest and central United States. In the midtroposp here, polluted layers with up to 250 ppbv CO, 150 pptv NO, and 1.8 ppbv NOy were observed within a deeper layer of enhanced O-3 mixing ratios (up to 8 8 ppbv) over the NAO at around 32 degrees N, 64-68 degrees W. These aircraf t observations, when coupled with ozone sondes, back trajectories, and sate llite image loops, indicate two distinct meteorological mechanisms that com bine to yield the observed chemical signature of the air. There is substant ial meteorological evidence, supported by ozone sonde observations and earl ier King Air flights, indicating that stratosphere/troposphere exchange ass ociated with the upstream frontal system injects and advects dry, ozone-ric h air into midtropospheric regions over the continent. These subsiding air masses have the potential to result in deep layers of enhanced ozone in the offshore postfrontal area. Convection from the developing (upwind) system appears to lift air from the continental boundary layer into the area of su bsidence in the mid to upper troposphere. The result is high concentrations of gaseous and particulate pollutants along with elevated quantities of oz one. Ozone mixing ratios exceed those attributable to boundary layer ventin g or in-transit photochemical production. These meteorological processes le ad to pollution and enhanced ozone from the stratosphere cooccurring in pos tfrontal air masses over the NAO.