Mixing of continental and marine air masses and en route chemical transformations in transPacific transport of aerosols: Lagrangian analysis of a single transport event.

Observations and model studies in the Western Pacific region report evolving aerosol size distributions and heterogeneous chemical transformation of Asian aerosols. Recent papers report sea salt mixing and acid- carbonate reactions in single particle analyses of Asian dust when sampled in Korea and Japan. Model studies indicate similar processes en route from Asia to North America, but direct observations of aerosol transformations in transit from Asia to North America have been lacking. Simultaneous operation of time-, size-, and elemental composition- resolving aerosol samplers in Korea and California captured both ends of a transPacific transport event in April, 2002 during the Intercontinental Transport and Chemical Transformation experiment (ITCT-2K2). These data permit direct observation of the interaction of Asian continental air with the Western Pacific marine boundary layer, as well as evaluation of the evolution of aerosol size distributions and chemical composition in transit over the North Pacific. Our results resolve questions about the mechanisms of mixing of continental and marine aerosols, help clarify the source regions of the Asian aerosols, and also show systematic, qualitative differences between processes in the Western and Eastern Pacific that explain apparent contradictions between the Korea/Japan shoreline data with observations from North America. In addition, such near and far field data can be used to validate transPacific aerosol transport modeling without need for accurate emission data.