Comprehensive Time-Resolved Molecular Speciation Of Gaseous And Particulate Organic Constituents In The Atmosphere

Organic chemicals comprise the dominant fraction of particulates found in atmospheric aerosols, and the largest proportions of these are secondary products formed in the atmosphere from oxidation of volatile organic compounds. Often these chemical transformations result from complex pathways involving species from different sources. To understand these processes, we need to be able to trace the transformation pathways from the emitted vapor species to the oxygenated, less volatile organic matter that comprises the organic aerosol. Proposed is expanding the capability of the Semi-Volatile Thermal desorption Aerosol Gas chromatograph (SV-TAG) instrument to add the measurement of more volatile VOCs which are important secondary organic aerosol (SOA) precursors. Both the VOC precursor and resulting SOA products will be measured by a single detector providing consistent quantification over 15 orders of magnitude of volatility in the comprehensive TAG (c-TAG) instrument. Phase I work developed a VOC collector compatible with the existing SV-TAG system and capable of measuring, identifying, and quantifying organic compounds within the volatility range equal to that of C5 to C16 alkanes. This range spans the dominant biogenic emissions of isoprene and monoterpenes, as well as many important anthropogenic alkanes and aromatics from fossil fuel use. In our Phase II effort we aim to combine these VOC and SVOC channels into a single instrument with a common mass spectrometer, to provide a fully automated, field-deployable instrument with on-line calibration. The proposed instrument will be the very first to comprehensively measure C5- C33 species hourly in-situ, including essentially all the major known primary precursors to secondary organic aerosols from biogenic and anthropogenic sources, along with many of their oxidation products. Combining these measurements in the proposed single comprehensive c-TAG instrument offers many compelling, practical advantages, including consistency through use of a common detector, lower costs, and a smaller footprint. Commercial Applications and Other Benefits: This instrument will be of practical use to the atmospheric research community, especially those now using aerosol mass spectrometers to measure bulk aerosol composition. The molecular level speciation from this instrument will provide insights into chemical transformation processes in the atmosphere that are important to particle formation, and indirectly to cloud characteristics and climate.