Mixing State, Morphology, and Optical Properties of Cook Stove Soot Coated with Alpha-Pinene SOA

Description

Direct radiative forcing by black carbon (BC)-containing aerosols (BCA) is affected by the relative fraction of non-BC material in the particle, and the particle morphology. 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 atmospherically-relevant flaming cook stove soot and a targeted examination of the core/shell space, using mobility size-selected soot. We coated the soot with alpha-pinene secondary organic aerosol (SOA), generated in a 2 cubic meter 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 nm mass-equivalent diameter) and SMPS-based shell/core diameter ratios from 1.3 to 2.5. Mie modeling predictions for absorption enhancement were found to be in line with experimentally-determined absorption enhancement, within uncertainties. In a follow-up experiment, polydisperse cookstove soot with thinner coatings was also examined, while adding a centrifugal particle mass analyzer and filter substrates for SEM/TEM imaging to the instrument mix. Results from these experiments will also be presented in this poster.