Seminar

Abstract

Comprehensive analysis of organic aerosol formation composition has been stymied by its complexity and lack of available measurement techniques. Novel instrumentation, analysis methods, and conceptual frameworks are introduced here for chemically characterizing complex hydrocarbon mixtures and ambient aerosols. This chemical information is used to gain insights into the formation, transformation and oxidation of organic aerosols, even in the absence of unambiguous identification of compounds. Traditional techniques rely on measuring specific “tracer” compounds, for which specific information is known about their emissions and oxidation precursors. Known compounds, however, represent only a very small fraction of the mass in organic aerosols, so new methods are presented here for characterizing complex mixtures based on structural and chemical properties, without sacrificing measurements of tracer compounds. Gas chromatography is coupled to high resolution time-of-flight mass spectrometry with vacuum ultraviolet (VUV) photo-ionization to identify the molecular mass and formula of unidentified compounds, a major step toward a comprehensive description of complex mixtures. These techniques are used here to characterize the structures of unknown compounds and formerly unresolvable mixtures, including a complete description of the chemical composition of two common petroleum products related to anthropogenic emissions: diesel fuel and motor oil. Full characterization of vehicular particle emissions and the composition and oxidation of petroleum products yields unprecedented detail about hydrocarbon emissions, new conclusions about the relative importance of vehicle fuels in the Los Angeles Basin, and an improved understanding of the role of compound structure and phase in the oxidation process. The application of these tools and frameworks toward a complete physiochemical characterization of ambient aerosol, and their extension to time-resolved gas chromatography instrumentation, will be discussed.