AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Mapping the Operation of the Miniature Combustion Aerosol Standard (mini-CAST) Soot Generator
RICHARD MOORE, Andreas Beyersdorf, Suzanne Crumeyrolle, Lee Thornhill, Edward Winstead, Luke Ziemba, Bruce Anderson, NASA Langley Research Center
Abstract Number: 478 Working Group: Combustion
Abstract Soot aerosol derived from combustion processes have been shown to affect the Earth’s radiation budget via direct absorption and scattering of solar radiation and by acting as cloud condensation nuclei (CCN) or ice nuclei (IN) to form clouds. In addition, ultrafine soot particles and associated polycyclic aromatic hydrocarbon (PAH) compounds likely pose significant health risks to the public. Consequently, much work in recent decades has focused on quantifying the properties of both ambient soot and that directly emitted from combustion sources. Relevant properties include soot concentration, size and morphology and the presence of inorganic and organic coatings on the soot surface. Investigating the role of each of these properties in determining climate and health impacts directly from ambient measurements is challenging because of low ambient mass loadings and because soot often coexists with atmospheric aerosol with a high degree of chemical complexity. Consequently, laboratory studies are needed to deconvolve these dependencies. A crucial component in these studies is having a reliable and reproducible combustion aerosol generator. A promising commercially-available generator is the Jing Ltd. Combustion Aerosol Standard (mini-CAST), which generates soot using a nitrogen-quenched, non-premixed, propane diffusion flame.
We present a comprehensive characterization of soot produced by the mini-CAST over the range of operating conditions, including variation of fuel, oxidation air, and mixing nitrogen flow rates. Measurements of particle size were found to be fairly constant and reproducible over a period of weeks to months, while number concentration varied due, in part, to soot accumulation in the flow system. In addition, OC-EC analysis from bulk filter measurements and SP2-derived coating thicknesses show a significant variation in residual organics including PAHs coating the soot surface over the range of measured sizes, which influences the effective density. The effectiveness of removing these coatings with a heated catalytic stripper will be discussed.