Abstract View
Detailed Characterization of Secondary Organic Aerosol Composition Using Multiple Mass Spectrometric Techniques
ERIK HELSTROM, Abigail Koss, Jordan Krechmer, Manjula Canagaratna, Frank Keutsch, Alexander Zaytsev, Jesse Kroll, MIT
Abstract Number: 647
Working Group: Instrumentation and Methods
Abstract
Chemical processing of gas-phase organic molecules in the atmosphere can lead to the formation of secondary organic aerosol (SOA). Because thousands of species can be involved in the chemical processing of organic carbon in both the gas and particle phase, tracking the evolving properties of SOA presents a formidable analytical challenge. Real-time chemical characterization of aerosol-phase mixtures can be achieved with a variety of mass spectrometric instruments, but there are important limitations on the capabilities of each individual measurement. “Hard” ionization techniques like Aerosol Mass Spectrometry (AMS) are suitable for the measurement of total particle carbon, but they are chemically nonspecific. By contrast, chemical ionization mass spectrometers (CIMS) can identify individual species but are more selective. Coupled with inlet schemes for phase-separated sampling, these CIMS allow for highly resolved measurements, but only of a subset of the total mixture. Any analytic assessment of the total carbon behavior from a single instrument therefore may be biased by omission of undetected species. In order to more comprehensively characterize SOA composition and behavior, we consider measurements of chamber oxidation experiments of various organic compounds taken by four mass spectrometers: AMS, Thermal Desorption-Proton Transfer Reaction-Mass Spectrometer (TD-PTR-MS), Thermal Desorption-Ammonium-CIMS (TD-NH4-CIMS), and Iodide-CIMS with a Filter Inlet for Gases and Aerosols (FIGAERO-I-CIMS). Carbon number, oxidation state, volatility, and nitrogen content are considered on the individual species level and for the total measured product distribution. These metrics allow for comparison between instruments, as a function of precursor identity and oxidant exposure. Overlaps between measurements are used to identify biases for different instruments and to construct a multi-instrument synthesis of measurements, enabling a comprehensive and quantitative measurement of organic aerosol composition. These measurements can then be compared with the composition of gas phase products and used for updated descriptions of organic carbon evolution and SOA formation.