HR: 10:50h
AN: A32A-03    [Abstracts]
TI: Estimation of the Mass Absorption Cross Section of the Organic Carbon Component of Aerosols in the Mexico City Metropolitan Area (MCMA)
AU: * Barnard, J C
EM: james.barnard@pnl.gov
AF: Pacific Northwest National Laboratory, PO Box 999, Richland, WA 99352,
AU: Volkamer, R M
EM: Rainer.Volkamer@Colorado.EDU
AF: University of Colorado, Dept. of Chemistry & Biochemistry; UCB 215 University of Colorado, Boulder, CO 80309-0215,
AU: Kassianov, E I
EM: evgueni.kassianov@pnl.gov
AF: Pacific Northwest National Laboratory, PO Box 999, Richland, WA 99352,
AB: Data taken from the MCMA-2003 and the MILAGRO field campaigns are used to examine the absorption of solar radiation by the organic component of aerosols. Using irradiance data from an MFRSR and an actinic flux spectroradiometer, we find aerosol single scattering albedo (SSA) as a function of wavelength. We find that in near-UV spectral range (defined here as 250 nm to 400 nm) the SSA is much lower than the SSA at 500 nm suggesting enhanced absorption in the near-UV range. Absorption by elemental carbon, dust, or trace gases (i.e., NO₂, SO₂, and others) cannot account for this enhanced absorption leaving only the organic part of the aerosol to account for it. We use data from a surface deployed Aerodyne Aerosol Mass Spectrometer (AMS) along with the inferred SSA and aerosol optical thickness to estimate the Mass Absorption Cross-section (MAC) for the organic carbon. We find that the MAC is about 10 m²/g at 300 nm and falls close to zero at about 500 nm. These MAC values can be considered as "radiatively correct" because when used in radiative transfer calculations the calculated solar fluxes match the measured fluxes at the wavelengths considered here.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0360 Radiation: transmission and scattering
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting