An In-Situ Instrument to Assess the Concentration and Phase Partitioning of Atmospheric Semi-Volatile Organic Compounds

Semi-volatile organic compounds are a significant, but poorly characterized fraction of atmosphere aerosols. Many are formed through photochemical processing of more volatile organics, and once oxidized tend to form less volatile compounds that condense into the particulate phase. Knowledge at the molecular level of their abundance and vapor-particle phase partitioning is needed to understand the relative roles of biogenic and anthropogenic emissions to the global burden of particulate organic matter, to elucidate atmospheric oxidation pathways, and to assess their impact on global climate. Our project goal is to develop and validate and in-situ method for the time-resolved quantification, at the molecular level, of the semi-volatile organic constituents in ambient air and their partitioning between vapor and particle phases. The instrument proposed here would provide in-situ, hourly quantification of semi-volatile organic material simultaneously in particle and vapor phases. In Phase I we demonstrated our capability to separately collect semi-volatile organic compounds in ambient air from particle and vapor phase, to thermally desorb and focus these semi-volatile organics onto the GC column and to analyze vapor and particle organic components by GC-MS in a manner consistent with our current TAG instrument. Measurements of ambient air showed consistent and expected results for the relative concentration and phase partitioning of a range of alkane and polycylic aromatic hydrocarbons. UIn Phase II we will develop our technology into a field-proven system for the automated, hourly measurement at the molecular level of the concentration and phase-partitioning of the semi-volatile organic compounds in ambient air. Specific tasks include the optimization of the vapor-particle collection and thermal desorption system, development of methodology for in-field system calibration, field demonstration of the fully integrated, automated instrument and demonstration of the utility of the data set for elucidating sources and atmospheric processing of organic matter. Commercial Applications and other Benefits as described by the awardee: This technology will advance our capability for real-time organic aerosol characterization by making possible for the first time the in-situ measurements of semi-volatile organics simultaneously in gas and particle phases. This technology will be attractive to multiple research groups with some aerosol mass spectrometry capability and experience, and to regulatory agencies responsible for monitoring air toxics