HR: 08:40h
AN: A41E-03    [Abstracts]
TI: Climate-Relevant Properties of Organic Carbon (OC) and Their Impact on Direct Radiative Forcing Estimate
AU: * Sun, H
EM: hsun4@uiuc.edu
AF: Department of Civil & Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Ave , Urbana, IL 61801-2352 United States
AU: Bond, T C
EM: yark@uiuc.edu
AF: Department of Civil & Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Ave , Urbana, IL 61801-2352 United States
AU: Koch, D
EM: dorothy.koch@yale.edu
AF: NASA Goddard Institute for Space Studies, Columbia University, 2960 Broadway, New York, NY 10027-6902 United States
AB: Organic carbon (OC) makes up a large fraction of atmospheric aerosols. The major sources of primary OC are combustion processes, primarily fossil-fuel burning, biofuel burning, and open biomass burning. OC is considered to mainly scatter solar radiation and thus cools the Earth system. Although there are hundreds or thousands of different organic species in atmospheric aerosols, global climate models to date have treated organics as one compound. However, organic aerosols exhibit widely varying climate-relevant properties (light absorption and water affinity) that cannot be represented by this assumption. To represent these varying properties, we developed a classification scheme: Climate-Relevant Optical & Structural Subgroups of OC (CROSS-OC). OC is divided into four groups that should be tractable for use in climate models. We estimate water activity by examining current studies on hygroscopic behavior of organic compounds. We characterize the differences between groups using hygroscopic growth factor (Gf), which is smaller than that of inorganic salts but non-negligible. We also account for light absorption by OC. We examine the absorption spectra of hundreds of organic compounds and estimate a correlation between light absorption and molecular structure. Polycyclic aromatic hydrocarbons (PAHs) and other compounds with conjugated unsaturated bonds could contribute to light absorption with a strong wavelength dependence. We estimate how much OC is emitted in each fraction for different sources by combining source characterization measurements, particularly results of molecular speciation. We provide a global emission inventory of primary OC and identify locations where sources of OC with different microphysical characteristics are prevalent. We model aerosol lifetime and direct radiative forcing for our four CROSS-OC groups in the Goddard Institute for Space Studies General Circulation Model (GISS GCM). We examine how the aerosol lifetime and radiative forcing predicted using CROSS-OC compare with previous predictions assuming uniform OC composition.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005