Spatial distribution and size evolution of particles in Asian outflow: Significance of primary and secondary aerosols during ACE-Asia and TRACE-P : Characterization of Asian aerosols and their radiative impacts on climate

[1] 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 μm 2 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 H 2 SO 4 -H 2 O-NH 3 . Growth rates of ∼2 nm h -1 can be explained by the condensation of sulfuric acid at a rate of 2 ± 1 × 10 6 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.