AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Real-time Evolution of the Gas-phase Precursors for Secondary Organic Aerosol from Biomass Burning
Adam Ahern, Patrick Veres, Daniel S. Tkacik, Ellis Shipley Robinson, Rawad Saleh, Albert A. Presto, Allen Robinson, Robert J. Yokelson, Neil Donahue, RYAN SULLIVAN, Carnegie Mellon University
Abstract Number: 484 Working Group: Biomass Burning Aerosol: From Emissions to Impacts
Abstract The chemical composition and evolution of biomass burning smoke is highly variable, both in the fresh near-fire emissions and in the aged plumes. Photochemical aging of the smoke plume can produce significant quantities of secondary organic aerosol (SOA) from the oxidation of gas-phase organic compounds. Field measurements, and simulated laboratory chamber experiments, have demonstrated a wide range of SOA enhancements in atmospherically aged smoke plumes. In some cases significant additional SOA mass is produced, while in others a net loss of organic aerosol mass occurred with aging. The chemical nature of the gaseous precursors and the mechanisms that determine the magnitude of SOA formation (or loss) remain largely unknown.
A unique dual smog chamber method was deployed at the Fourth Fire Laboratory at Missoula Experiments (FLAME-IV) to address this deficiency in our understanding of how biomass burning smoke evolves in the atmosphere, and its total contribution to aerosol loadings. Here we focus on the relationship between the variability and evolution of the gas-phase precursors and the resulting variability in SOA production or loss. Chamber aging experiments were conducted using a range of globally relevant biomass fuels, and different atmospheric aging conditions including exposure to UV blacklights, ozone, and nitrogen oxides. The two identical 7 m$^3 Teflon chambers were simultaneously filled with diluted smoke from combustion using realistic, unconstrained burn profiles with varying contributions from flaming and smoldering-phase combustion. This dual chamber experiment (DUCE) method facilitated paired control/perturbed experiments with the same complex, realistic, but difficult to reproduce smoke emissions. The gas and particle emissions were measured in real-time and analyzed to establish possible correlations between reactant decay rates, volatile organic compound formation, and SOA formation. Two proton transfer reaction mass spectrometers measured the loss rates of less-oxidized gaseous SOA precursors and the formation of more oxidized products from atmospheric aging.