AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
A New Method for Robust, Moderate-Cost Measurement of Oxygen, Carbon, and Sulfur Content of Organic Compounds and Mixtures
James Hurley, Nathan Kreisberg, Braden Stump, Patricia Keady, Susanne Hering, GABRIEL ISAACMAN-VANWERTZ, Virginia Tech
Abstract Number: 341 Working Group: Instrumentation and Methods
Abstract Health and climate impacts of aerosols depend on their composition. In particular, oxygen content controls the tendency of particles to form clouds, may drive adverse health effects, and provides insight into atmospheric oxidation processes. However, current methods to measure particle composition either rely on filter collection with low time resolution, or advanced mass spectrometers operated by highly-trained on-site personnel. We are developing an instrument for the time-resolved, in-situ measurement of aerosol organic carbon and its oxygen-to-carbon ratio, as well as aerosol sulfur. The approach is semi-continuous system, with concentrated particle collection coupled to commonly used gas analyzers, namely flame ionization (FID), flame photometric (FPD) and non‐dispersive infrared (NDIR) absorption based detection of CO2. We demonstrate that the average per-carbon-atom response generated by an FID is proportional to the oxygen content of an analyte. We quantify this relationship by directly measuring carbon dioxide produced in FID for ~100 individual atmospherically-relevant analytes. With this data, we are able to estimate oxygen-to-carbon ratios to within ~0.1 across the range of 0 to 1, and this relationship is shown to be valid for simple multi-component mixtures. FPD detection of sulfur within the same flame is shown to additionally provide quantification of inorganic and organic sulfur-containing compounds. We demonstrate the coupling of this detector train to online particle collection and stepped thermal desorption, providing the basis of an instrument that will enable remote, autonomous, and easy-to-calibrate measurements of particle composition (C, O, and S content) and particle volatility. Sensitivity of this approach is expected to allow measurements of the concentration and O:C of ambient organic aerosols at levels as low as ~1 µg/m3 with hourly time resolution.