HR: 0800h
AN: A31C-0066    [Abstracts]
TI: Optical, Physical, and Chemical Properties of Soot in Aerosol Samples From the UAE
AU: * Semeniuk, T A
EM: Trudi.Semeniuk@asu.edu
AF: Department of Geological Sciences/Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287 United States
AU: Garvie, L A
EM: lgarvie@asu.edu
AF: Department of Geological Sciences/Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287 United States
AU: D\'{o}dony, I
EM: idodony@asu.edu
AF: Department of Geological Sciences/Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287 United States
AU: Buseck, P R
EM: pbuseck@asu.edu
AF: Department of Geological Sciences/Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287 United States
AB: Soot from the fine-fraction of aerosol samples collected in the lower troposphere (1.2 km) during the summer of 2002 over the Gulf of Oman (UAE) was characterized using high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). The soot occurs in aggregates of individual spherules up to 40 nm in diameter. Each consists of an amorphous nucleus around 3 nm in diameter, surrounded by a 2- to 15-nm concentric band of graphene segments with 3.5-nm spacings. Two structure types are readily distinguishable. Type one has a single nucleus surrounded by a broad zone of concentric graphene, and type two has multiple amorphous nuclei within the core, surrounded by graphene stacks that become longer and more concentric towards the spherule perimeter. Both types have amorphous coatings 1- to 3-nm thick, but they are typically broader on type two. The soot optical properties were investigated for the UV-VIS region using EELS. The surface low-loss spectra are characterized by well-defined peaks within the visible range at 240, 340, and 553 nm. In contrast, bulk spectra from the cores of the spherules are characterized by a gradual rise in spectral absorbance, with a maxima at 209 nm, corresponding to the $\pi$ to $\pi$* inter-band transitions of graphite. Thus, chemical and structural differences between soot cores and rims may correlate with measurable optical differences. Since the high surface area and amorphous surfaces of the soot potentially affect its behaviour within the atmosphere, we will investigate the relationship between the optical, chemical and structural properties of soot in more detail. Scanning transmission electron microscopy combined with EELS will allow us to probe the nature of the amorphous surface layers as well as measure optical properties of the different graphene nanostructures.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting