Measuring Gas Phase Diesel Exhaust Organics by PTR-MS in Field and Laboratory Experiments

Emissions of gas phase organics from diesel engine exhaust are thought to be a significant pool of precursor material for the formation of secondary organic aerosol (SOA) in urban areas. The abundance and atmospheric chemistry of these compounds are poorly understood. We show that thermal desorption sampling coupled to a proton transfer reaction mass spectrometer (TD-PTR-MS) can quantify the abundance of larger organic compounds emitted in diesel engine exhaust such as long chain alkanes, monocyclic aromatics, and cyclic alkanes. Measurements of diesel engine and gasoline engine exhaust by PTR-MS reveal similar mass spectra for the volatile organic compound range but significant differences for higher molecular weight organics such as alkanes and monocyclic aromatics found in diesel fuel. The TD-PTR-MS method was deployed for 2 weeks during the Carbonaceous Aerosol and Radiative Effects Study (CARES) in Sacramento, CA. Results from laboratory sampling of engine exhausts and field data will be shown to illustrate the viability of the analytic method to quantify the abundance of diesel engine gas phase organic compounds in urban air.