AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Composition and Mixing Timescale Measurements of Biomass-burning Aerosol and Secondary Organic Aerosol from alpha-pinene Using Two Particle Mass Spectrometers
ADAM AHERN, Ellis Shipley Robinson, Daniel S. Tkacik, Rawad Saleh, Robert J. Yokelson, Albert A. Presto, Allen Robinson, Neil Donahue, Ryan Sullivan, Carnegie Mellon University
Abstract Number: 708 Working Group: Aerosol Physics
Abstract The composition of atmospheric aerosol can change significantly as freshly emitted aerosol is processed in the atmosphere. The mixing of secondary compounds with the existing aerosol cores can lead to changes in the aerosol’s properties, such as its hygroscopicity and volatility. The insoluble core can also provide important information for source apportionment, and affect the optical properties of these internally-mixed aerosols.
During the fourth Fire Lab at Missoula Experiments (FLAME IV), we investigated the mixing timescales of biomass smoke with biogenic SOA. Smoke from biomass burning was used to fill two environmental chambers. alpha-pinene-derived secondary organic aerosol (SOA) formed via ozonolysis in a separate Teflon bag was introduced to the larger smoke-filled environmental chamber and allowed to mix while being simultaneously monitored by two particle mass spectrometers.
We probed the mixing timescale using a Light-Scattering Aerosol Mass Spectrometer (LS-AMS), and a new Single-Particle Mass Spectrometer (SP-MS). These instruments use thermal desorption/electron ionization, and laser ablation, respectively, for aerosol compositional analysis. Particle clustering algorithms were used to identify homogeneously nucleated SOA particles from the single-particle mass spectrometry data, to observe their mixing dynamics with the primary smoke aerosol. Although the size distribution from the AMS was inconclusive with respect to mixing, tracer ions K$^+ and C$_2H$_3O$^+ were used to identify some smoke particles and SOA, respectively. The ensemble aerosol mass spectrum measured by the AMS changed rapidly to reflect the addition of the nucleated SOA and the SP-MS measured particles that contained both K$^+ and C$_2H$_3O$^+ soon after mixing, suggesting rapid mixing. However, particles containing the SOA tracer and devoid of K$^+ persisted for several hours.