Date of Award
Civil and Environmental Engineering
Atmospheric aerosols -- Analysis, Atmospheric aerosols -- Environmental aspects
In the atmosphere, biogenic and anthropogenic emissions are oxidized to form secondary organic aerosols (SOA); however, the identities and concentrations of the compounds formed are inadequately known. In this work an aerosol (gas+particle) collection system was designed and tested in order to more fully characterize atmospheric volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs) that contribute to SOA. Target compounds to be collected were C6 to C20 compounds with oxygenated functional groups such as aldehydes and alcohols. The collection system was designed to allow characterization of atmospheric aerosols using multiple analytical methods: two-dimensional gas chromatography with time of flight-mass spectrometry (GCxGC-TOFMS), with and without derivatization, and two- dimensional liquid chromatography with mass spectrometry (LCxLC-MS). The first stage of collection in the system uses a polytetrafluoroethelyne (PTFE) filter to capture the low volatility compounds in the particle phase. The flow is then split for two different collection mechanisms: adsorption thermal desorption (ATD) cartridges for gas phase VOCs, and solid phase extraction (SPE) filters for SVOCs. In order to test the viability of aerosol collection on PTFE filters and subsequent analysis using derivatization, four aerosol samples were collected on PTFE filters at Reed College. The average mass collected over 4 trials was 10.15 μg. The U.S. Department of Energy Environmental and Molecular Science Lab (EMSL) performed extraction and derivatization on the Reed College samples, followed by GC-MS. Results show identifiable peaks that are significantly different than the filter blanks, suggesting that derivatization methods can be used to facilitate identification of relatively polar organic compounds sampled onto PTFE filters. Additional aerosol collection trials were conducted at Portland State University (PSU) using two SPE filters in series to collect gases and particles from tobacco smoke. A literature review was conducted to determine the type of SPE filter, time, and necessary flow rates to collect an optimum amount of sample for analysis. The tobacco smoke PM mass collected was 6mg/2mg and 2mg/0.9mg for trials one and two, respectively (front/back filter). PSU tobacco smoke samples were analyzed at EMSL using GC-MS with derivatization. Results showed successful collection of polar compounds in the semi-volatile range of interest, including alcohols, aldehydes, and phenols. Next steps of this research include collecting aerosol samples with the whole system (PTFE + ATD + SPE) and subsequent analysis of samples using GCxGC-TOFMS, with and without derivatization, and LCxLC-MS. Results to date suggest a more complete characterization of atmospheric organic aerosols can be attained using multiple offline analyses. Further characterization of atmospheric organic aerosols is necessary to improve air quality and climate modeling and develop efficient air quality and climate change mitigation technologies.
Fairbaugh, Craig, "Methods of Collecting and Separating Atmospheric Organic Aerosols for Analysis Using Two-Dimensional Gas and Liquid Chromatography with Mass Spectrometry" (2015). University Honors Theses. Paper 149.