During the period April 1989 through December 1990, O3 concentrations in the marine boundary layer at Barbados, West Indies, show a pronounced seasonal cycle. Daily averaged values in the winter and spring often fall in the range of 25--35 ppbv for periods of several days, and they seldom fall below 20 ppbv. In contrast, during the summer, values typically fall in the range of 10--20 ppbv. During the winter-spring period, there is a very strong negative correlation between O3 and a number of aerosol species, including NO3-. These anticorrelations appear to be driven by changing transport patterns over the North Atlantic as opposed to chemical reactions involving O3 and nitrogen species in the atmosphere. Analyses of isentropic trajectories clearly show that high O3 and low NO3- are associated with transport from higher latitudes and high altitudes. Conversely, high NO3- and relatively low O3 are associated with transport from Africa. Our study suggest that North America and the middle troposphere (and stratosphere) are not strong sources for NO3- over the tropical North Altantic.

The strong correlation of NO3- with 210Pb and the weaker correlation with Saharan dust indicates that NO3- is derived principally from continental surface sources, probably in Europe and North Africa, but not from the Saharan soil material itself. During several extended periods, NO3- and 210Pb were strongly correlated and their concentrations were high relative to nss SO4=; these factors, coupled with trajectories originating in Africa, suggest that African biomass burning was a significant source at these times. In contrast, biomass burning appears to be a minor source for O3 as measured at Barbados, perhaps accounting for an enhancement of about 5 ppbv at most during these periods. ¿ American Geophysical Union 1992