Quasi-Lagrangian aircraft measurements above the Yellow Sea, East China Sea, and Sea of Japan revealed synoptic-scale secondary aerosol formation and condensational growth during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) and Transport and Chemical Evolution over the Pacific (TRACE-P) experiment. This occurred in the presence of pollution and mineral dust aerosol surface areas as high as 1200 ¿m2 cm-3. Concentrations of sulfuric acid generally appeared insufficient for binary nucleation, but observations, models, and theory are consistent with a ternary nucleation mechanism involving H2SO4-H2O-NH3. Growth rates of ~2 nm h-1 can be explained by the condensation of sulfuric acid at a rate of 2 ¿ 1 ¿ 106 molecules cm-3 s-1. Aerosol volatility suggested increasing neutralization of the aerosol during growth. Size distribution measurements suggest that weak (mean condensation nuclei (CN) 3--13 nm ≈ 500 cm-3) new particle production was a common occurrence in the region. However, new particle production was enhanced by ~1 order of magnitude (mean CN 3--13 nm ≈ 5000 cm-3) in postfrontal air masses associated with offshore flow during cloud-free conditions. Fog and clouds appear to be regionally important in modulating nucleation events through scavenging of secondary aerosol and through depletion of gas-phase precursors through enhanced heterogeneous chemistry. Our results indicate that only 10--30% of the total aerosol population consists of aged secondary aerosols after ~2 days of transport from source regions. In spite of their high production during nucleation events, secondary aerosols advected out over the Pacific Ocean will have a small impact upon indirect forcing and a negligible impact upon direct forcing compared to primary aerosol emissions and the species that condense upon them.