Development of a Thermal Desorption Tube Sampler and Cryo-GC-MS Method for the Measurement of VOCs in Biomass Burning Plumes

Abstract:

Volatile organic compounds (VOCs) are commonly used to distinguish regional biomass burning emissions from those that have undergone long-range transport. This study focuses on acetonitrile, which is a robust tracer for biomass burning due to its relatively long atmospheric lifetime (weeks to months). By quantifying this tracer in atmospheric samples, we can not only identify biomass burning emission sources over varying spatial scales but also determine the effect of biomass burning on pollution events, such as the production of ozone, in remote or urban areas.

We use PoraPak N as a collection medium for both background and elevated levels of acetonitrile and other VOCs in discrete atmospheric samples. Thermal desorption tubes are inserted into a multi-tube active sampler, where each tube is capable of sampling between approximately 5 and 30 liters of ambient air over the course of 2-8 hours. After collection, we analyze these samples using thermal desorption into a cryofocusing trap with subsequent gas chromatography (GC) for separation and detection by a mass spectrometer (MS). To test the field deployment of this technique, we collected samples of both background ambient air and air that was impacted by biomass burning plumes at the Mount Bachelor Observatory (MBO) in central Oregon during summer and fall 2015. Based on previous studies by Wang et al. (2007) and others cited therein, we expect to see ambient concentrations at MBO between 0.1 and 10 ppb of acetonitrile.

Long-term active sampling by multiple thermal desorption tubes along with analysis of these samples via Cryo-GC-MS provides a portable, low-maintenance method of measuring biomass burning tracers in remote or urban areas. With this technique, we can further investigate the relative impacts of regionally and long-range transported biomass burning emissions on air quality during high pollution events.