AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Soot Aggregate Restructuring Due to Coatings of Oleic Acid and Dioctyl Sebacate
Rouzbeh Ghazi, JASON OLFERT, University of Alberta
Abstract Number: 122 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract It is generally accepted that aerosols can affect climate and Earth's temperature by the scattering and absorption of sunlight. A large positive component of this radiative forcing from aerosols is due to soot that is released from the burning of fossil fuel and biomass. Freshly emitted soot particles are typically hydrophobic and fractal and mostly externally mixed with non-refractory compounds. Once emitted into the atmosphere, soot particles undergo several aging processes, and non-refractory compounds will condense on them. Soot particles in the atmosphere have different amounts of coating, and the morphology and optical properties of soot can change depend on coating thickness.
In this study, the effect of coating thickness on the morphology of soot particles is investigated by using oleic acid and dioctyl sebacate coatings. A wide range of coating thicknesses was used, with up to 12 times as much coating as the mass of the soot. It is shown that as the coating mass increases the degree of collapsing increases, but after the mass coating fraction becomes more than five, the change in diameter of the black carbon core is not significant. A model is presented to predict the change in mobility diameter after coating/denuding process. The change of effective density of soot particles in coating/denuding processes is reported. As the coating mass increases the effective density drastically increases and after that it slightly decreases. After denuding the coated particles the effective density increases due to particle collapsing. Condensing coating material on the soot causes the shape factor to drastically decrease to one and become constant for a mass coating ratio of five. After a coating/denuding process the shape factor decreases compared to fresh particle. Upon coating, the mass-mobility exponent increases from 2.14 to 3.02 (for highest mass coating fraction) and after denuding decreases to 2.38.