Master of Philosophy
School of Chemistry
Roulston, Christopher Thomas, Emissions of fine particulate matter from tropical peat fires, Master of Philosophy thesis, School of Chemistry, University of Wollongong, 2018. https://ro.uow.edu.au/theses1/280
This thesis describes the work undertaken to determine the rate at which particulates are emitted from tropical peat fires in peninsula Malaysia. The emission of particulate matter (PM) during wild fire events around the world contributes to many negative effects on both communities in the local vicinity and (through transport mechanisms) other locations around the globe. These negative effects include; pre-mature mortality, decreased lung function and quality of life, and a decrease in yields from crops in farming regions due to aerosol loading. Despite all of these ill effects, very little is known about the particulate emissions from tropical peat fires. This thesis aims to address some of the knowledge gaps within current research.
There are three main components to this thesis. The first describes a weeklong study hosted at the Victoria University, Werribee campus. This study compared numerous particulate-matter measuring instruments within a smoke chamber. The study was conducted by introducing wood smoke, coal smoke and diesel exhaust into the chamber, which was mixed and held at predefined concentrations before being allowed to return to background levels. The Office of Environment and Heritage (OEH), Lidcombe, NSW, provided; an Aurora 1000G Ecotech Nephelometer, a Thermo Scientific Model 48i Gas Filtration CO Analyser and a DustTrak-DRX 8533 aerosol monitor to be used for this Masters research. The smoke chamber study provided evidence that the instrumentation to be deployed on further field studies through this project provided accurate and precise results (within the estimated uncertainties) when compared to a gravimetric standard.
The second part of this thesis describes the initial Malaysian field campaign. This campaign focused on peat fires in peninsula Malaysia, measuring the levels of carbon monoxide (CO) and PM with an aerodynamic diameter less than or equal to two and a half microns (PM2.5), within the smoke plumes from the fires. The emission factor of CO was determined using an open path MIDAC FTIR (Fourier Transform Infrared) spectrometer operated by Thomas E. L. Smith from Kings’ College London. The ratio between PM2.5 and CO measured in the smoke plume was multiplied by the emission factor for CO to determine an emission factor for PM2.5. The results from this study showed a trend not previously observed in the field, that as a peat fire ages the emission ratio of PM2.5 decreases. This anti-correlation between age and levels of PM2.5 released, provided the basis for a new hypothesis: as the peat fire progresses below the surface, an increasingly deep ash layer is formed, which filters PM2.5 from the smoke, thus lowering the emission ratio of PM2.5.
The third section of this thesis was an expansion of the second study, where a laboratory study was conducted to provide further evidence to test the hypothesis from the previous campaign. This study used peat that had been sourced from the same fields as the initial campaign. It was then dried and bulk density measured to ensure consistency between samples. Three laboratory burns were undertaken in total, each lasting in excess of 40 hours. The fires were ignited using nichrome wrapped around a ceramic plate that had a charge run through it to generate a flameless ignition. In the first two burns the fire could progress normally for many hours, and then (when particulate emissions had declined substantially) the layer of ash was carefully removed from the surface and the fire allowed to progress once more. The third burn was an ash addition experimental fire: about an hour after the ignition of the burn, a layer of pre-incinerated ash was added across the surface of the burning peat. Samples from this ash layer were taken at different depths and stages of the burn and tested to examine the carbon content. If the carbon content of the ash increased as the burn progressed, this would be further evidence that the ash layer was a sink for the missing PM2.5 from the measured emissions. The results from these burns confirmed the hypothesis that as fires burn the PM2.5 emissions reduce despite the combustion efficiency remaining stable. The ash addition experiment yielded positive (although not statistically definitive) results showing an increase in percentage carbon after the conclusion of the burn.
The results from this Masters thesis provide additional knowledge about the nature of peat fires and their emissions of PM. The findings can be used within fire emissions inventories and coupled with chemical transport models, to better understand the effects that large scale tropical peat fires can have on regional air quality and climate.