Influences of Aging on Soot, Dust and Nucleated Aerosol in Asian Aerosol

We studied size resolved aerosol physio-chemistry in Asian outflow over the Pacific during the spring of 2001 as part of the ACE-Asia and TRACE-P experiments. Soot was found to be generally internally mixed with condensable species (eg. sulfate) within less than one day transport from sources. These data also reveal interactions between pollution and dust aerosol in regions of strong pollution that result in the accumulation of condensable species (eg. sulfate) onto the dust. High temperature (stable at 300C) organic aerosol is also inferred to be present on the soot that can change the soot optical properties. As much as one half of the soluble species normally condensed upon the soot can end up on the dust during the highest dust events encountered. These modify the chemical characteristics of the dust mode and can change the relative composition of the pollution mode. These changes have significant effects upon the optical properties of the pollution mode as well as the scattering response to increasing humidity, f(RH). Hence, these dust and pollution must be modeled interactively in these regions in order to correctly describe these properties. Recently nucleated aerosol were often present at high concentrations in elevated regional pollution events over hundreds of kilometers in extent. However, the occurrence and concentrations of these aerosol were reduced by their exposure to fog or cloudy conditions present in the region during their transport. These events can influence both their nucleation and subsequent growth. Coupled with coagulation with larger aerosol associated with primary emissions (eg. soot) their concentrations are usually rapidly depleted after a day or two. As a result, these recently nucleated aerosol were often greatly reduced after aging. These observations indicate that the Asian aerosol advected over the Pacific is dominated by the primary emissions that determine the optically-active aerosol sizes responsible for their direct radiative effects and also most cloud condensation nuclei (CCN), with nominal diameters over 80nm, that are responsible for their indirect effect.