Year of Award

2012

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Chemistry

Department or School/College

Department of Chemistry and Biochemistry

Committee Chair

Robert Yokelson

Commitee Members

Christopher Palmer, Anna Klene, Garon Smith, Richard Field

Keywords

Biomass burning, Monoterpenes, Ozone, Plume chemistry

Publisher

University of Montana

Abstract

Biomass burning (BB) is the second largest source of trace gases and the largest source of primary fine carbonaceous particles in the global troposphere. BB trace gases and particles are of both regional and global importance. In the US, prescribed fire and wildfire are the two major fire types and they occur frequently. Prescribed fires are ignited to improve and aid forest health, maintenance, and management. Land managers strive to minimize the impact of smoke on local communities. However, smoldering combustion can still occur, leading to complaints of smoke exposure and reduced visibility. It is clear that we need better understanding of prescribed fire emissions both for the sake of land managers who conduct these burns and for the communities affected by smoke. In October-November of 2011 we measured the trace gas emission factors from seven prescribed fires in South Carolina, U.S. using two Fourier transform infrared spectrometer (FTIR) systems and whole air sampling (WAS) into canisters followed by gas-chromatographic analyses. A total of 97 trace gas species are reported here from both airborne and ground-based platforms making this one of the most detailed field studies of fire emissions to date. The measurements included the first data for a suite of monoterpene compounds emitted via distillation of plant tissues during real fires. The known chemistry of the monoterpenes and their measured abundance suggests that they influenced post-emission formation of ozone, aerosol, and small organic trace gases such as methanol and formaldehyde in the sampled plumes. The variability in the terpene emissions in South Carolina (SC) fire plumes was high and, in general, the speciation of the emitted gas-phase non-methane organic compounds was surprisingly different from that observed in a similar study in nominally similar pine forests in North Carolina around 20 months earlier. On the other hand, the HCN/CO emission ratio is fairly consistent at 0.9 percent for airborne fire measurements in coniferous-dominated ecosystems further confirming the value of HCN as a biomass burning indicator/tracer. The SC results also support an earlier finding that C3-C4 alkynes may be of use as biomass burning indicators on the time-scale of hours to a day. It was possible to measure the chemical evolution of the plume on four of the fires and significant ozone (O3) formation (O3/CO from 10-90 percent) occurred in all of these plumes. Slower O3 production was observed on a cloudy day with low co-emissions of NOx and the fastest O3 production was observed on a sunny day when the plume almost certainly incorporated significant additional NOx by passing over the Columbia, SC metro area. Due to rapid plume dilution, it was only possible to acquire high quality downwind data for two other species (formaldehyde and methanol) on two of the fires. In all four cases significant increases were observed. This is likely the first direct observation of post-emission methanol production in biomass burning plumes and the precursors likely included terpenes.

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© Copyright 2012 Sheryl Kashi Akagi