10th International Aerosol Conference
September 2 - September 7, 2018
America's Center Convention Complex
St. Louis, Missouri, USA

Abstract View


UV-visible Absorption Spectrum of Laboratory-generated Soot Particles

Al Fischer, Taylor Helgestad, Lindsay Renbaum-Wolff, Andrew Lambe, Arthur J. Sedlacek, Christopher Cappa, Andrew Freedman, Timothy Onasch, Paul Davidovits, GEOFFREY SMITH, University of Georgia

     Abstract Number: 1326
     Working Group: Carbonaceous Aerosol

Abstract
The absorption by soot particles generated from a methane inverted diffusion flame burner was measured across the UV-visible region of the spectrum. Two cavity ringdown (CRD) laser photoacoustic spectrophotometers (PASs) (405 nm and 532 nm), a lamp/laser PAS (301 nm - 662 nm), and a cavity attenuated phase shift single-scattering albedo monitor (CAPS PMSSA) (630 nm) were employed to measure absorption of suspended particles at a total of 10 different wavelengths. In general, very good correlation between the instruments was found with correlation coefficients, R2, of at least 0.93. Mass absorption coefficients (MACs) were calculated from measurements of particle mass made using a single particle soot photometer (SP2) and a centrifugal particle mass analyzer (CPMA), resulting in an interpolated value at 550 nm of 7.54 (± 0.43) m2/g. A power law function with the commonly assumed values of absorption Ångström exponent (AÅE) = 1.0 and MAC550 = 7.5 m2/g is found to describe the visible part of the spectrum well, but it underestimates UV absorption where the discrepancy is as high as 22%. A power law fit to the entire spectrum yields an AÅE of 1.21 (± 0.08), but a systematic increase in AÅE with decreasing wavelength was observed. It is shown that Mie theory with particles represented by volume-equivalent spheres is not adequate to reproduce the shape of the spectrum regardless of refractive index used. On the other hand, the use of a modified Rayleigh-Debye-Gans approximation with a single, wavelength-independent refractive index is able to do so, though it underestimates MAC values by 25-35% depending on the value of the refractive index used.