OS and pH estimation from AMS measurements and OH oxidation of phenolic compounds in wildfire smoke

Melinda Schueneman,
ANYL 3rd year student, [cires1.colorado.edu/jimenez-group/ Jimenez Group]

"This talk will focus on two unrelated research projects: the first will highlight a paper recently published in AMT, and the second will introduce and show preliminary results for a biomass burning project. Shortened abstracts are included here for reference.

Part I: Sulfate can be present in aerosols as inorganic (mainly ammonium sulfate, AS) or organosulfate (OS). Although OS is thought to be a smaller fraction of total sulfate in most cases, recent literature argues that this may not be the case in more polluted environments. Two new methods have been proposed to quantify OS separately from AS with AMS data. We use observations collected during several airborne field campaigns covering a wide range of sources and air mass ages and targeted laboratory experiments to investigate the proposed OS methods. Four chemical regimes are defined. In polluted areas with high ammonium nitrate concentrations and in remote areas with high aerosol acidity, the decomposition and fragmentation of sulfate in the AMS is influenced by multiple complex effects, and estimation of OS does not seem possible with current methods. In regions with lower acidity (pH > 0) and ammonium nitrate (fraction of total mass < 0.3), the proposed OS methods might be more reliable, although application of these methods often produced nonsensical results. Under highly acidic conditions (when calculated pH < 0 and ammonium balance < 0.65), sulfate fragment ratios show a clear relationship with acidity. The measured ammonium balance is a promising indicator of rapid estimation of aerosol pH < 0, including when gas-phase NH₃ and HNO₃ are not available. These results allow an improved understanding of important intensive properties of ambient aerosols.

Part II: The intensity and frequency of fires has been sharply increasing with an expanding population, increased land clearing for agriculture, and climate change. Fire plumes introduce large amounts of diverse chemical species into the atmosphere. The abundant emissions of VOCs, particles, and NO_x suggest that substantial aerosol formation should occur downwind of fires. However, typically no enhancement of total OA is observed in most field studies. To explore the relationship between POA and SOA in aging smoke, we use measurements from the Extractive Electrospray Soft Ionization Time-of-Flight Mass Spectrometer (EESI) taken during FIREX-AQ, along with EESI and Vocus measurements from chamber experiments. A suite of laboratory chamber experiments, targeting known and suspected BB SOA precursors, are being conducted to identify key tracer species in this system, for both the particle and gas phases. Key chemical species from the OH initiated oxidation of phenol, catechol, and styrene were identified from chamber studies and their formation and evolution were modeled with KinSim. Some identified products were calibrated for and identified in a FIREX-AQ research flight, and one plume was also modelled in KinSim. We present preliminary results from the analysis of these observations."