HR: 1340h
AN: A53A-0168    [Abstracts]
TI: Inferring dust composition from wavelength-dependent absorption in AERONET data
AU: * Koven, C D
EM: charlie@atmos.berkeley.edu
AF: Berkeley Atmospheric Sciences Center, 301 McCone Hall, Berkeley, CA 94720-4767 United States
AU: Fung, I
EM: inez@atmos.berkeley.edu
AF: Berkeley Atmospheric Sciences Center, 301 McCone Hall, Berkeley, CA 94720-4767 United States
AB: Atmospheric mineral dust is an important component of the Earth System, affecting climate and biogeochemical cycling. We present an inverse method of inferring dust composition from wavelength dependence of light absorption and the complex refractive indices of aerosol components. Specifically, we separate absorption by black carbon from absorption by hematite and organic carbon. We apply this method to coarse-mode-dominated AERONET observations in the "dust belt" region of globe, and identify differences between dust optical properties and composition in different locations. We solve for dust composition using two opposite, bracketing hypotheses of the state of mineralogical mixing: purely internal mixing and purely external mixing. We find that calculated absolute hematite concentrations are highly sensitive to mixing assumptions, while relative geographic and seasonal patterns are less sensitive to mixing assumptions. Internal mixing calculations appear to underestimate absolute hematite concentrations, while external mixing overestimates hematite concentrations. Inversions calculated assuming external mixing are better able to explain the wavelength dependence of dust absorption by only varying hematite concentration than inversions using internal mixing, which require substantial covariation between BC and hematite to match observations. Saharan and East Asian dust show higher hematite content than dust from Arabia. Saharan dust also shows seasonal variation in hematite content which may reflect seasonal shifts in dust source areas.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0365 Troposphere: composition and chemistry
DE: 1610 Atmosphere (0315, 0325)
DE: 3337 Global climate models (1626, 4928)
DE: 3394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005