10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Making Quantitative Measurements in Environmental Chamber Studies of VOC Oxidation and SOA Formation: Evaluating and Accounting for Potential Sources of Error
JULIA BAKKER-ARKEMA, Paul Ziemann, University of Colorado
Abstract Number: 1512 Working Group: Aerosol Chemistry
Abstract Controlled environmental chamber studies are important for determining atmospheric reaction mechanisms and identifying and quantifying gas and aerosol products formed in the oxidation of volatile organic compounds (VOCs). Such information is necessary for developing detailed chemical models for use in predicting the atmospheric fate of VOCs and also secondary organic aerosol (SOA) formation. However, complete analyses of atmospheric reactions, including both gas and particle phase product yields, branching ratios, and uncertainties, are difficult to achieve. When conducting laboratory chamber experiments, care must be taken to account for all the potential sources of error. For this work, we developed and evaluated a systematic approach for minimizing uncertainties by quantifying the gas- and particle-phase products of the oxidation of terminal alkenes by hydroxyl radicals in the presence of NO. Based on the results, we propose standard methods of accurately measuring chamber volume, adding precursors to the chamber, collecting gas- and particle-phase samples, and accounting for losses of vapors and particles to the chamber walls. We also investigated the generation of authentic standards with carefully calibrated mass measurements and corrections for solvent mass contributions. Particle-phase products were analyzed in real time with a thermal desorption particle beam mass spectrometer, and off-line by collection onto filters and subsequent analysis of functional groups by derivatization-spectrophotometric methods developed in our lab. Derivatized products were also separated by liquid chromatography for molecular quantitation by UV absorbance and identification using chemical ionization-ion trap mass spectrometry. Gas phase aldehydes were analyzed off-line by collection on a 5-channel denuder and subsequent analysis by gas chromatography, or by collection onto DNPH-coated cartridges and subsequent analysis by liquid chromatography. We demonstrate that when the proposed steps are taken to reduce the inherent uncertainties associated with environmental chamber experiments, we can comprehensively and accurately analyze the composition of complex mixtures of organic particles and gases formed in laboratory chamber studies.