Measurement of Organic Atmospheric Transformation Products by Gas Chromatography

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Abstract
The photooxidation of hydrocarbons in the atmosphere leads to the formation of organic species which are typically more polar in character than the parent compounds. In recent years, detailed hydrocarbon measurements for C1 to C10 alkanes, alkenes, and aromatics in the atmosphere have involved the use of deactivated canisters and gas chromatography, similar to that described by EPA Method TO-14. However, quantitative measurements of atmospheric polar organic compounds by this method are unreliable. Work in this laboratory frequently involves the analysis of sample mixtures from smog chambers that are used to simulate urban atmospheres for studying the formation of ozone and other potentially hazardous compounds. Over the past several years we have developed an inert cryogenic sampling system and related GC methods for the analysis of the photochemical mixtures which are sensitive, reproducible and provide adequate separation for non-polar hydrocarbons and their polar transformation products. These improvements have allowed a number of kinetic and mechanistic studies to be conducted, which in the past have only been possible using in-situ Fourier Transform Infrared Spectroscopy. This paper describes the system development including current strengths and limitations as applicable to experimental programs requiring measurements of polar organic compounds at near-atmospheric concentrations.