AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Absorption Enhancement of Monodisperse Cook Stove Soot Coated with alpha-Pinene SOA: Measurements and Modeling
Georges Saliba, Adam Ahern, Rawad Saleh, James Liacos, Eric Lipsky, Ryan Sullivan, Allen Robinson, R. SUBRAMANIAN, Carnegie Mellon University
Abstract Number: 612 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Direct radiative forcing by black carbon (BC)-containing aerosols (BCA) is affected by the relative fraction of non-BC material and the particle morphology – collectively referred to as “mixing state”. Bond and Bergstrom (2006) predict a range of absorption enhancements depending on the shell/core diameter ratio of a BC particle coated with non-BC material. Recent field work by Cappa et al. (2012) suggests a lack of absorption enhancement in ambient aerosol, in contrast to laboratory experiments using flame-generated BC and dioctyl sebacate. We conducted BC mixing experiments using more atmospherically-relevant flaming cook stove soot and a targeted examination of the core/shell space, using mobility size-selected soot and coating it with alpha-pinene secondary organic aerosol (SOA), generated in a 2 m$^3 Teflon chamber after injection and characterization of the nascent soot. A suite of instruments, including two photoacoustic extinctiometers (PAX-405, PAX-532), an SMPS, a soot particle aerosol mass spectrometer (SP-AMS), and a single-particle soot photometer (SP2) were used to characterize three nascent core diameters (100, 130, and 150 BC nm mass-equivalent diameter) and SMPS-based shell/core diameter ratios from 1.3 to 2.5. Preliminary Mie modeling is in line with experimentally-determined absorption enhancement, within experimental and modeling uncertainties. The leading edge only (LEO) optimization technique is used to determine the coating thickness of BCA. Preliminary results indicate the maximum shell/core diameter ratio based on the SP2 as 1.7-1.8, smaller than the SMPS-determined 2.3-2.5. The poster will explore these differences further.