Air mass characterization and source region analysis for the Gosan super-site, Korea, during the ACE-Asia 2001 field campaign

This paper presents results of air mass characterization and the associated microphysical and optical properties of Asian aerosols, using the cluster analysis technique for classifying air mass back-trajectories arrived at Gosan on the Jeju Island, Korea during the ACE-Asia campaign. Five distinct clusters of trajectories were taken to explain each transport regime. The temporal variation of the transported air masses could be well explained by the consecutive and stepwise change of air masses between statistically classified clusters. The cluster-mean trajectory exhibited its close relationship with the synoptic-scale circulation pattern. In addition, it was shown that the composite of mean sea-level pressure field is useful for explaining favorable meteorological conditions for long-range transport of dust and anthropogenic pollution in East Asia. The highest light scattering and absorption coefficients for sub-10- and submicron aerosols as well as highest concentrations of 222Rn and condensation nuclei are associated with the air mass types accompanying dusts and pollutants. The cluster-mean single scattering albedo (SSA) for sub-10- and submicron aerosols ranged 0.88–0.90 and 0.81–0.86, respectively. This value of SSA indicates the large contribution of submicron aerosol for the light absorption in East Asia. The concentration of 222Rn and aerosol microphysical and optical properties for marine air mass suggests that the marine air masses are somewhat influenced by continental outflows. The minor differences in aerosol microphysical and optical properties among continental clusters with similar routes and different transport speed implies that the effect of transport speed may not be significant if the transport routes are similar.