THE IMPACT OF UNITED-STATES CONTINENTAL OUTFLOW ON OZONE AND AEROSOL DISTRIBUTIONS OVER THE WESTERN ATLANTIC

Aircraft measurements of selected trace gas species, aerosols, and met eorological parameters were performed in the lower troposphere off the U.S. east coast during August and September 1989 as part of the NASA Global Tropospheric Experiment (GTE) Chemical Instrumentation Test and Evaluation (CITE 3) expedition. In this paper, we examine these data to assess the impact of continental outflow on western Atlantic O3 and small aerosol budgets. Results show that mixed layer (ML) O3 concentr ations and small aerosol number densities (Np) were enhanced by factor s of 3 and 6, respectively, within airmasses of predominantly continen tal origin compared with clean maritime background air. These enhancem ents exhibited a marked altitude dependence, declining rapidly above t he ML to the point where only slight to moderate differences in O3 and Np, respectively, were notable above 2.4 km. Within continentally inf luenced ML's, both O3 and Np were correlated with CO, exhibiting linea r regression slopes averaging 0.4 ppb V(O3)/ppbv(CO) for O3 and 7.7 (p articles cm-3)/ppbv(CO) for Np and indicating a primarily anthropogeni c origin for the observed enhancement of these species. Comparisons be tween profiles in continental and background maritime air masses sugge st that photochemical production below 1.4-km altitude adds over 10% t o western Atlantic tropospheric column O3 abundance in continental out flow regimes. For aerosols, eastward advection of low-level continenta l air contributes an average net flux of 2.8 metric tons of submicron (accumulation mode) particles per kilometer of shoreline per day to th e western Atlantic troposphere.