Characterizing the physical and chemical evolution of organic aerosol in biomass burning smoke using molecular tracers from laboratory and FIREX-AQ observations

Abstract:

Biomass burning is an increasingly important topic in atmospheric science and air quality, as the intensity and frequency of fires have been rising with an expanding population, increased land clearing for agriculture, and climate change. Fire plumes introduce large amounts of diverse compounds into the atmosphere, which have been shown to negatively impact human health and the environment. This diversity also makes characterizing fire impacts challenging. The abundant emissions of VOCs, particles, and NOx suggest that substantial aerosol formation should occur downwind of fires. However, often no enhancement of total OA with atmospheric aging is observed, including most plumes sampled during the FIREX-AQ mission. One explanation that has been proposed before and we are exploring is that POA evaporation is balanced by the condensation of VOC precursors onto existing aerosols (forming SOA). During the FIREX-AQ mission, an instrument capable of directly measuring molecular species in aerosol in real-time (1 Hz), an Extractive Electrospray Soft Ionization Time-of-Flight Mass Spectrometer (EESI-ToF) was deployed on the NASA DC-8. While the identity of some key molecules is clear based on previous literature and other evidence, most of the hundreds of species detected in the fire plume aerosols are not yet identified, and potentially hold essential information needed to understand the overall chemical evolution of OA. A suite of laboratory chamber experiments, targeting known and suspected BB SOA precursors and POA, are being conducted to identify key tracer species in this system, for both the particle phase (EESI-ToF) and the gas phase (Vocus PTR-TOF). Key chemical species, such as phenols (catechol and phenol), furans (furfural and methylfurfural), and aromatics (styrene), their oxidation products, and the fate of those products are being investigated. We use a box model (KinSim) and the GECKO model to simulate these experiments, guided by field observations, to identify new products, constrain POA and SOA budgets, and thus better interpret and chemically quantify the evolution of aerosols in biomass burning plumes.