AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Effect of Secondary Organic Aerosol Coating Thickness on the Detection and Characterization of Biomass-burning Soot by Particle Mass Spectrometry
ADAM AHERN, R. Subramanian, Georges Saliba, Eric Lipsky, Allen Robinson, Neil Donahue, Ryan Sullivan, Carnegie Mellon University
Abstract Number: 496 Working Group: Instrumentation and Methods
Abstract Biomass burning is a large source of highly light absorptive black carbon (BC) particles with a wide range of morphologies and sizes. The net radiative forcing from these particles is strongly dependent on the amount of internally mixed secondary material, such as secondary organic aerosol (SOA) that can condense as a biomass-burning plume ages in the atmosphere. Accurate real-time measurements of BC in aging plumes are important to constrain mass absorption enhancements, particle lifetimes, and emissions.
Past studies have shown that for BC surrogates and urban emissions, changing the amount of organic mass on nascent soot can affect the sensitivity of real-time instrumentation, like particle mass spectrometers. The fractal-like BC particles increase in size and also become more spherical with the condensation of secondary material. Both of these changes decrease the particle beam divergence (thereby increasing particle collection efficiency) in instruments like Aerodyne’s aerosol mass spectrometer (AMS) and the laser ablation aerosol particle mass spectrometer (LAAPTOF).
We investigate the response of three commercial particle mass spectrometers to monodisperse biomass-burning particles as they are coated with SOA from alpha-pinene ozonolysis in the CMU smog chamber. Particles from biomass burning are less spherical than the surrogate BC, and contain inorganics (e.g. K$^+) that may have important ion plume effects for laser desorption ionization, as used in the LAAPTOF. Three soot core sizes, each with three successive coatings of SOA, were investigated. The soot particle (SP)-AMS measured particle beam divergence (as a function of size and shape) and the light scattering (LS)–AMS measured particle bounce off the vaporizer. The LAAPTOF showed a highly linear mass spectral response to the OC/EC mass ratio in individual particles. This demonstrates the capacity to obtain quantitative mass measurements of aged soot particle composition from single-particle mass spectrometry, using realistic particles with complex morphologies and composition.