HR: 16:00h
AN: A14B-01    [Abstracts]
TI: Radiative forcing by brown carbon and mixed black carbon: a probabilistic approach
AU: * Bond, T C
EM: yark@uiuc.edu
AF: University of Illinois at Urbana-Champaign, Dept. of Civil & Environmental Engineering NCEL MC-250 205 N. Mathews Ave., Urbana, IL 61801, United States
AU: Sun, H
EM: hsun4@uiuc.edu
AF: University of Illinois at Urbana-Champaign, Dept. of Civil & Environmental Engineering NCEL MC-250 205 N. Mathews Ave., Urbana, IL 61801, United States
AU: Roden, C A
EM: croden@uiuc.edu
AF: University of Illinois at Urbana-Champaign, Dept. of Civil & Environmental Engineering NCEL MC-250 205 N. Mathews Ave., Urbana, IL 61801, United States
AB: Climate-relevant properties of organic carbon aerosols, including hygroscopicity and light absorption, are not well known. Most sources emit a mix of black (strongly-absorbing) carbon, organic (less-absorbing) carbon, and secondary aerosol precursors. Therefore, the climate-relevant properties of these materials and their mixtures should be known in order to determine the effect of individual sources on radiative forcing. Although direct radiative forcing due to organic carbon might be smaller than that of other aerosol constituents, this contribution might determine whether forcing by individual sources is positive or negative. We recommend UV-visible spectra and hygroscopic properties that are appropriate for representing organic carbon. These values are based on literature synthesis and laboratory experiments. Organic material from some sources absorbs light ("brown carbon"), while other organic carbon does not. We implement these properties in the Community Atmosphere Model (CAM), along with a global emission inventory which identifies the sources from which brown carbon is emitted. In addition, we use new parameterizations of mixing between strongly absorbing aerosol (black carbon) and non-absorbing aerosol. We estimate total radiative forcing by mixed and unmixed black carbon, brown carbon, and non-absorbing carbon. Finally, we present a two-box model used to calculate radiative forcing. Source, transport and sink processes are calibrated to match recent AEROCOM model results. Normalized forcing (forcing per mass) is taken from CAM simulations. We use reported atmospheric and laboratory measurements to constrain uncertainties in emission rates, transport processes, and optical properties and perform Monte Carlo simulations of forcing due to individual sources. We also estimate the contribution of secondary aerosols and indirect effects. Transport processes, particularly wet deposition and convection, are large sources of uncertainty. Despite uncertainties, the probability that aerosols from some emissions sources produce positive radiative forcing is quite high. For other sources, uncertainties prevent unequivocal determination of the sign of radiative forcing.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0365 Troposphere: composition and chemistry
DE: 1622 Earth system modeling (1225)
DE: 3311 Clouds and aerosols
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting