Year

2009

Degree Name

Doctor of Philosophy

Department

Department of Chemistry - Faculty of Science

Abstract

This thesis describes work aimed at improving our knowledge of emissions to the atmosphere from Australian vegetation fires. The thesis contains three main parts. First there is a study to characterise the emissions from forest fires in southeast Australia. This uses ground-based Fourier transform infrared solar absorption spectroscopy, coupled with ultra-violet/visible spectroscopy, to explore the properties of smoke plumes from Australian forest fires that passed over the observation site at Wollongong, in New South Wales, Australia (34.4°S, 150.9°E). The particulate loading in the smoke plumes is characterised by the aerosol optical depth, measured at visible wavelengths. Vertically integrated amounts of a several emitted trace gases are also determined, (limited to those detectable by solar absorption spectroscopy in the infrared). Enhanced trace gas amounts of carbon monoxide, hydrogen cyanide, formaldehyde, ammonia, acetylene, ethylene, ethane, formic acid and methanol were measured in the smoke plumes and quantified via the use of emission ratios. The emission ratios determined in this study indicate that emissions from fires in southeastern Australian forests (which are predominantly eucalypts) are broadly similar to those from other geographical regions except for comparatively low emissions of ethane. The second part of this thesis describes a new method of making estimates of gaseous emissions from fires. Strong correlations between trace gases and aerosol optical depth (AOD) in smoke plumes are used in conjunction with satellite-based measurements of AOD to estimate the total amounts of carbon monoxide and other gases emitted from the Canberra fires of 2003. There are significant difficulties with the new method, in particular the interruption of the satellite record due to clouds or technical problems with the satellite. Nevertheless the estimated emissions of carbon monoxide from the Canberra fires (4.9 – 9.6 Tg), is in agreement with an estimate made by existing techniques. The addition of another tool for making estimates of gaseous emissions from biomass burning is useful for corroborating existing techniques, especially since the sources ofuncertainties inherent in the different techniques are largely independent of one another. The third part of the thesis is a study to characterise the emissions from savanna fires in the tropical north of Australia. Again ground-based Fourier transform infrared solar absorption spectroscopy is used with automated measurements in the near infrared from a site in Darwin, Northern Territory, Australia, (12.4°S, 130.9°E). Alternatively measurements in the mid infrared can be made by overriding the automated system, and this has been done when there is evidence of significant smoke plumes in the area. Total column amounts of carbon monoxide from Darwin from 2005-2008 show a very clear annual cycle, with evidence of transported pollution from Indonesian fires in 2006. The time series agrees within the expected uncertainties with measurements of carbon monoxide derived from the MOPITT satellite instrument, giving greater confidence to MOPITT retrievals in the tropics. Mid infrared spectra have been recorded through smoke plumes over Darwin on 20 separate days, yielding column amounts of carbon monoxide, formaldehyde, acetylene, ethane and hydrogen cyanide and emission ratios with respect to carbon monoxide for the four latter gases from tropical north Australian savanna fires. Emission ratios for acetylene and ethane from this work are in broad agreement with other literature values, whilst emission ratios for formaldehyde and hydrogen cyanide are significantly higher than the only previous field measurements from Australian savannas (but in agreement with laboratory studies) suggesting storage losses in the earlier study.

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