| Summary: | 碩士 === 國立清華大學 === 分子醫學研究所 === 101 === ABSTRACT
Biomass is widely used as energy source in rural households in Asia. Biomass burning comprises the incineration of wood, charcoal and agricultural waste as household fuel or in form of the combustion of crop residues on farm fields. Smoke emissions from biomass burning have a significant impact on global atmospheric chemistry, as they constitute a large source of particulate matter as well as carbon monoxide, nitrogen oxides, and hydrocarbons, especially in the tropics and subtropical regions. Therefore, biomass burning has attracted the attention of the general public, scientists and policy makers globally due to its contribution to air pollution and the effects of these emissions on human health and climate. This thesis evaluates the chemical characteristics of biomass burning aerosol in Vietnam and in Taiwan and investigates the impact of post-harvest burning of rice fields on the air quality in Taiwan and in Vietnam in comparison. Concentrations of inorganic anions and cations, as well as selected organic compounds, including molecular tracers for biomass burning (anhydrosugars) and fungi (sugar alcohols), were measured in air samples (both ambient air and near-source samples) from the two countries. Ion concentrations in air samples from Vietnam were higher than those in the Taiwan air samples. An analytical method based on high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) was used to measure the isomeric anhydrosugars (levoglucosan, mannosan, and galactosan) as well as the fungal spore tracers (arabitol and mannitol) in the biomass combustion aerosol. Levoglucosan concentrations were observed during the biomass burning season in Vietnam at higher levels than in Taiwan air samples collected in the rice field burning season. In addition, the relatively high levoglucosan/mannosan ratios of 21.2 (Son La) and 20.6-45.2 (Da Nang) clearly indicated that rice straw was a major type of fuel that was burned in the biomass burning season in Vietnam. Likewise, organic carbon (OC) and elemental carbon (EC) concentrations in Vietnam were much higher than in Taiwan. However, the OC/EC ratios in Vietnam were relatively lower than those in Taiwan in the spring 2012 biomass burning season. A very high OC/EC ratio implies important influence from biogenic sources and/or biomass burning activities. The fungal tracer concentrations (arabitol and mannitol) in Vietnam were higher than those in Taiwan. In addition, statistically significant correlations were found between the simultaneously observed fungal tracers (arabitol and mannitol) and biomass burning tracers (levoglucosan and K+), suggesting that these species were emitted by co-located sources, and hence the elevated fungal tracers were likely associated with biomass burning activities at Son La, Vietnam. Furthermore, long-range transport of biomass burning smoke emissions from Southeast Asia (especially Vietnam) has been shown for the first time affecting downwind areas by smoke particle transport across the South China Sea to the sampling sites in Taiwan, under the influence of the prevalent monsoon winds, using molecular characteristics of the ambient aerosol particles in the source region and receptor sites.
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