Field and Laboratory Measurements of Biomass Burning and Vehicle Exhaust Using a PTR-MS
VanderSchelden, Graham Samuel
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The Proton Transfer Reaction Mass Spectrometer (PTR-MS) is a powerful tool for analyzing organic compounds in air and has been applied in field and laboratory applications to assess emissions from biomass burning and vehicles. Biomass burning is an important source of air pollution globally in the form of wild fires, burning of crop stubble, and combustion of organic material for home energy. In the United States, residential wood combustion combined with low inversion heights in winter time has caused air quality problems. Through field deployment of the PTR-MS in Xi’an China during August of 2011, it was determined that 27%, 16%, 26%, and 12% of ambient carbon monoxide (CO), acetaldehyde, benzene, and toluene could be attributed to biomass burning. The PTR-MS was also deployed to Yakima, Washington in January of 2013, finding that residential wood combustion was a substantial source of air toxics and PM. Residential wood combustion contributed 100%, 73%, 69%, 55%, 36%, 19%, 19%, and 17% of organic PM1, formaldehyde, acetaldehyde, black carbon, benzene, toluene, C2-alkylbenzenes, and CO respectively. Diesel vehicles are becoming a larger fraction of the vehicle fleet and can be held responsible for a substantial fraction of air pollution emissions from on and off road mobile sources. Diesel engines are a source of low volatility products that are difficult to measure and are thought to be important in the formation of secondary organic aerosol (SOA). This work focuses on measuring important diesel exhaust compounds with the PTR-MS and assessing oxidation processes of these compounds. When the PTR-MS was deployed to the field along with a thermal desorption preconcentration system, we estimated that diesel vehicles were about 3-15% of the vehicle activity influencing our study site in Yakima, WA using the ratio of m/z 157 to m/z 129. SOA yields of diesel exhaust compounds were assessed and about 48% of the SOA was attributed to compounds measured by the PTR-MS; with 21% attributed to alkylbenzenes, 20% attributed to alkanes, 3% attributed to alkylnaphthalenes, 3% attributed to molecular weight 178 polycyclic aromatic hydrocarbons, and 1% attributable to cycloalkanes.