HR: 0800h
AN: A41D-0736    [Abstracts]
TI: Optical Analysis of Coated and Uncoated Soot: Data for Global Climate Change Models
AU: * Bueno, P A
EM: pedro@umd.edu
AF: University of Maryland, Department of Chemistry Bldg 091, College Park, MD 20742, United States
AU: Winter, S
EM: swinter@umd.edu
AU: Stehr, J
EM: stehr@atmos.umd.edu
AF: University of Maryland, Atmospheric and Oceanic Science Department Bldg 224, College Park, MD 20742, United States
AU: Mulholland, G
EM: georgewm@umd.edu
AF: University of Maryland, Department of Mechanical Engineering Bldg 088, College Park, MD 20742, United States
AU: Dickerson, R
EM: russ@atmos.umd.edu
AF: University of Maryland, Department of Chemistry Bldg 091, College Park, MD 20742, United States
AU: Dickerson, R
EM: russ@atmos.umd.edu
AF: University of Maryland, Atmospheric and Oceanic Science Department Bldg 224, College Park, MD 20742, United States
AU: Zachariah, M
EM: mrz@umd.edu
AF: University of Maryland, Department of Chemistry Bldg 091, College Park, MD 20742, United States
AU: Zachariah, M
EM: mrz@umd.edu
AF: University of Maryland, Department of Mechanical Engineering Bldg 088, College Park, MD 20742, United States
AB: Atmospheric aerosols play a fundamental role in Earth's atmospheric chemistry and climate. Soot is an absorbing aerosol, though the magnitude of that absorption has largely been determined by measuring the optical properties of uncoated soot. It has been proposed that coated soot might absorb radiation more efficiently than uncoated soot, thus warming the climate more than previously suspected. For this study, soot is generated in a well-controlled Santoro-Style diffusion flame burner with ethylene as the fuel, and has been successfully coated with dibutyl phthalate (DBP). DBP has a refractive index of 1.490 (real part), which is similar to the refractive index of sulfuric acid (n=1.426) at 589 nm. DBP is substituted for the commonly found sulfate coated particles for several reasons including safety and instrument integrity. By changing the temperature of the DBP, the vapor pressure of the DBP is changed and consequently, the coating thickness can be changed. The aerosols are measured with a differential mobility analyzer (DMA). From the DMA the aerosols are sent to a condensation particle counter for size distributions or are analyzed. Optical analysis performed with a multi-pass extinction and scattering cell (MPESC) where the total scattering and extinction cross-sections are measured. The MPEC uses a 632nm laser and a 100 m path length. The absorbance cross-section is calculated from those measurements. This study improves upon previous optical studies of soot by using soot particle sizes that are representative of primary soot particles in the atmosphere providing a more solid and viable result.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting