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J. Christopher Doran Pacific Northwest National Laboratory P.O. Box 999/K9-30 Richland, WA 99352 email: christopher.doran@pnl.gov We hypothesize that the shift from an externally mixed state to an internally mixed one will result in significant modifications to the optical properties of aerosols as they age and are advected downstream from an urban source. We propose to use field and laboratory measurements, analyses, and mesoscale modeling to study those modifications and their radiative impact. We will examine and characterize the changes in aerosol light scattering, absorption, optical depths, and surface radiative fluxes in an urban plume as it is advected between two sites downwind of an urban area and separated by 100 to 200 km with travel times of 3 to 12 hours. We will conduct a detailed analysis of the meteorological conditions during the field campaign to identify what aspects of the observed changes in aerosol properties are attributable to factors such as transport, diffusion and dilution, and relative humidity effects. We will then ascertain what aspects must be attributed to modifications in the chemical and microphysical properties of the aerosols, e.g., their mixing state. In particular, we will use three methods to study the evolution of the specific absorption of black carbon (BC) and attempt to relate it to the aging and mixing state of those aerosols. A key component of our proposal is to organize and conduct a field measurement campaign to facilitate studies of the life cycles of aerosols, by us and others, over the desired distance and time scales. The field measurements will be supplemented by a laboratory study to help characterize the chemical behavior of atmospheric soot and the times required for significant changes in its mixing state as it ages, and to relate those changes to changes in the specific absorption. [back to ASP ST Membership] |