Asian influence over the western North Pacific during the fall season: Inferences from lead 210, soluble ionic species and ozone

Aerosol samples collected over the western Pacific during the NASA/Global Tropospheric Experiment Pacific Exploratory Mission (PEM-West A) expedition (September October 1991) revealed mean Pb-210 concentrations in the free troposphere in the 5 - 10 fCi m(-3) STP range. Most soluble ionic aerosol-associated species were near detection limits [<< 40 parts per trillion by volume (pptv)] in these same samples. The altitude distribution of O-3 near Asia closely resembled that of Pb-210, while no relationship was found between the concentrations of O-3 and Be-7. Free tropospheric air over the western Pacific was depleted in soluble aerosol-associated species but enriched in Pb-210 and O-3, indicative of deep wet convection over the Asian continent. The influence of Asian air on the composition of the free troposphere over the western Pacific was evident on most of the PEM-West A flights. However, evidence of continental influence was largely restricted to those species that are relatively insoluble (or have insoluble precursors), hence escape scavenging during vertical transport from the boundary layer into the free troposphere by wet convective activity.