title: Investigation of Physiochemical Properties of Size-resolved Biomass Burning/Local Wildfire Aerosols
Creators: name: Ordou, Niloofar
Publisher: name: Griffith University
Year: 2021
Subjects: subject: particulate matter (PM)
subject: biomass burning (BB)
subject: Poly Aromatic Hydrocarbons (PAH)
subject: Black carbon (BC)
subject: organic carbon (OC) content
subject: fuel
subject: Australia
subject: burning emissions
subject: Toohey Forest
subject: burning phases

description: Overall, particulate matter (PM) and household air pollution are at the root of 2.9 million deaths annually. One of the sources of particulate matter is biomass burning (BB) smoke. These particles can be formed by natural fires, prescribe agriculture fires, and as a result of burning fuel for cooking and heating houses. BB smoke particles can have various health effect and environmental impacts depending on a number of factors. Altering ozone refraction, they can act as cloud condensation nuclei. Health risks associated with these particle have been studied for long. Pulmonary, heart, carcinogen (especially due to compounds like Poly Aromatic Hydrocarbons (PAH). First and foremost, the nature of the fuel has a direct impact on the composition of the particulate matter and gaseous particles formed as the combustion products. Woody, Grass, or leafy fuels have been found to be composed of different compounds with different mass fractions. For example, cellulose content in wood is higher than other types of biomass fuel. As a results, it is logical to seek similar compound ending up in the particulate matter. The scale and intensity of the fire is the other influential factor. Although the effect of natural wildfire (bushfire) smoke particles would not be as direct and immediate as those evolving from the fuel burnt in household uses, long term effect of exposure to these particles spreading within the atmosphere month and even years after the fire has happened should not be overlooked. Besides, in very close vicinities to the fires, in fresh smoke less than minutes old, there always exist high number of finer particles which are health-wise of more concern compared to larger particle (as these finer particles penetrate into lower parts of the respiratory system through diffusion). Weather conditions, like elevation, wind speed, humidity, and sunlight are also influential factors in the formation of these particles. The other crucial factor is the phase of burning, i.e. Ignition, flaming, mixed state, and smouldering. Numerous studies have investigated the effect of these conditions on the size distribution, number concentration and physiochemical properties of smoke particles. PM properties of BB smoke have been investigated all around the globe for different biomass types and different burning conditions. Black carbon (BC) and organic carbon (OC) content of the PM are the most documented investigated items as they contributes to the high mass percentage of the PM. Other ubiquitous PM components include anhydrosugars, alcohols, PAHs, acids, water soluble ions, and trace elements. Gaseous particles resulted from BB carry with them sulphur oxides (SOx) and nitrogen oxides (NOx), volatile and semi volatile organic compounds. Each of these compounds and materials are known to have serious health and climate impacts. Numerous studies have used different devices and technologies to investigate the effect of fuel type and amount, and phase of burning and operational mode on different properties of fresh and aged smokes in case of small scale controlled or laboratory burns, massive natural wildfires, or air-forced cook stove gasifiers. In Australia, despite contributing to more than 7% of biomass burning emissions annually, there are quite a few exhaustive studies on the properties of bushfire particles. The importance of research redoubles considering the mega-fires taking place in Australia 2019-2020 which ravaged an estimate of 19 million hectares. This study is aimed to make a contribution in filling this gap and finding novel ideas in order to investigate different factors influencing Australian local vegetation fires which could potentially effect the environment and human health. Three journal articles are published based on this study, parts of which are used in different sections throughout this report. Citations are made in the beginning of the main relevant chapters. Abstract summaries are presented briefly here: First paper: Under controlled laboratory settings and small scale fires of vegetation collected from Toohey forest, it was found that leaves classification burn with flaming dominant phases producing intense black smoke which is consisted of larger particles as opposed to more smouldering-dominant burning of the branch and grass classifications releasing white smoke emissions which contain finer particles. Elemental analysis detected nine main elements in all three classifications and in three size fractions of smoke particulate matter samples (from 14.1μm to below 2.5μm). Potassium, a biomarker, was the most prevalent element among the samples followed by sulphur. Less abundant elements were found to be Na, Al, Mg, Zn, Si, Ca, and Fe. Second paper: Particle size distribution in biomass smoke was observed for different burning phases, including flaming and smouldering, during the combustion of nine common South Queensland Australian vegetation representatives. Smoke particles generated during smouldering phase of combustions were found to be coarser as compared to flaming aerosols for all hard species. In contrast, for leafy species this trend was inversed. In addition, the combustion process was investigated over the entire duration of burning by acquiring every second data for all nine species. Particles were separately characterised in two categories: fine particles (diameter below 200nm), and course particles with the diameter larger than 200nm. It was found that fine particles contribute to more than 90 percent of the total fresh smoke particles for all investigated species. Third paper: smoke samples were collected during prescribed fire burns conducted between May 2018 and August 2019across different regions in Toohey forest, Queensland, Australia. Particle size/mass distribution as well as size-segregated elemental content were measured and the results were compared against the values obtained from the combustion of similar vegetation mixture under controlled laboratory settings. It was found that the concentration levels of coarse particles (sizes above 1 μm) were higher during field burn events, whereas the contributions of PM1 (smaller than 1 μm) was higher in case of laboratory burns. Following elemental analysis of different size classes of smoke particles (&lt;0.96μm, 0.96-2.5μm, and &gt;2.5μm) confirmed the presence of eight elements in both laboratory and field cases (Na, K, Mg, Ca, Zn, Al, Fe, S), however, levels of Ca, Mg, Al, and S were noticeably higher in prescribed fire results. Observed discrepancies between field and laboratory data could be attributed to the effect of top soil and duff layers present in prescribed fires/natural wildfires and absence thereof in the laboratory burns, which reveals the influential role of the aforementioned layers on the overall air quality status across bushfires-affected areas.