Comprehensive, Time-Resolved Molecular Speciation of Gaseous and Particulate Organic Constituents in the Atmosphere

Development of new instrumentation for measuring volatile organic compounds (VOC) and intermediate volatility organic compounds (IVOC) that may react to form secondary organic aerosols (SOA) has been identified as a vital need by DOE. Revealing the detailed mechanisms leading to SOA formation from gas phase precursors is best achieved by measuring both phases with sufficient temporal resolution to track the rapidly changing chemical composition and atmospheric conditions that directly affect these reactions. Owing to the enormous range of volatility encompassed by VOCs and OA no single instrument currently exists that can measure both precursors and their SOA products at the molecular level. Proposed is expanding the capability of the Semi-Volatile Thermal desorption Aerosol Gas chromatograph (SV-TAG) instrument to add the measurement of I/VOCs via in-situ thermal desorption GC/MS with online derivatization. Both the precursor and resulting SOA products will be measured by a single detector providing consistent quantification. Further, using an aerosol collector ahead of the I/VOC measurement provides a regenerating filter to avoid a current limitation on stand-alone gas phase instruments when dealing with semi-volatile or polar compounds. Phase I work will focus on adapting our aerosol sampling and GC/MS interface to the collection of gas phase compounds and demonstrate the improved detection capabilities of TOFMS compared to QMS for analysis of ambient air. Key elements of the dual system will be tested during Phase I before fully integrating the two sides during Phase II work. Additionally, we will optimize the derivatization method for use on highly polar ambient I/VOCs without perturbing analysis of the non-polar components. Compounds to be tested will include previously identified SOA tracer compounds, including high polarity multifunctional organics. Phase II efforts will produce an in-situ instrument capable of hourly comprehensive organic speciation of the full range of I/VOCs through non-volatile aerosols employing a pair of miniature gas chromatographs. The expanded measurement system will remain compatible with the TAG-AMS currently under commercialization by Aerodyne Research Inc. and offers expanded capabilities for an important segment of the atmospheric research community. Besides elucidating crucial atmospheric processes, this in-situ instrument could (1) provide insights into atmospheric toxins affecting human health, (2) identify contributions to urban pollution from different combustion fuel types, and (3) yield information on compounds that affect the hygroscopicity and optical properties of aerosols.