| dc.description.abstract | Biomass burning produces a great amount of greenhouse gases and aerosols, which cause not only local air pollution and regional acid rain but also affect the formation of clouds and thus regional radiation balance as well as global climate change.
Every spring season, biomass burning is frequently occurred in the Southeast Asia. Under the transport of an appropriate weather system, the air mass can carry the produced pollutants. This study chose Lu-lin Mountain (2,862 m a.s.l.) situated in central Taiwan for observation on aerosols from long-range transport. The observations include background periods in Autumn and December in 2004 and event period in April 2005. In addition, the experiment was conducted to sample aerosols near the burning source of rice straw and pine. The analyzed aerosol properties include mass concentration, water-soluble ion, carbonaceous content, monosacchride anhydrides, and dicarboxylic acids.
The results show that PM2.5 average in the period of long-range transport biomass burning was 15.4 μg m-3, which was clearly three times than that of the background observation. For water-soluble ions, the dominant species were ammonium and sulfate both in the background observation and in the the period of biomass burning. However, potassium ion observed in the biomass burning was three times more than that of the background. For carbonaceous content, volatility-corrected OC (OCpy) was increased significantly during the biomass burning event. The low temperature (EC1-OP) was dominant in elemental carbon (EC). Aerosol levoglucosan, which is considered as a cellulose burning tracer, was observed higher at an average of 46.5 ng m-3 during the biomass burning event. From the collection of cloud and fog aerosol, both sulfate ion and EC were found higher than background samples.
In the study of near source biomass burning, the results showed that the aerosol produced was predominant in the fine mode. Water-soluble ions were dominated by chloride and potassium ions. In terms of carbon fractions, high-temperature voltilized OC3 was the most important species and EC1-OP was the major species in EC. In addition, the results of different combustion phases showed that smoldering phase emitted more fine aerosols than flaming phase. However, the water-soluble ions were in greater amount for flaming phase than smoldering phase. As for carbonaceous fractions, the ratios of high-temperature voltilized OC4 and OCpy in OC for flaming phase were greater than those of smoldering phase. In contrast, smoldering phase had greater ratios of low-temperature voltilized OC2 and OC3 in OC than those of flaming phase.
For aerosol tracer study, potassium ion and carbons were found useful in comparing aerosols from near source and long-range transport. The K+/EC values for long-range transport and near source of biomass burning were 0.25 and 0.36, respectively. Meanwhile, the values of EC/TC for long-range transport and near source of biomass burning were 0.18 and 0.09, respectively. For OC/EC, the values were 4.58 and 9.13, respectively, for long-range transport and near source of biomass burning. Furthermore, the ratio of total dicarboxylic acids to levoglucosan was calculated at around 4.55. In using the ratio of levoglucosan to potassium ion as a reference for assessing different phases of biomass burning, the value was 0.023 for flaming phase and 0.044 for smoldering phase. In summary, this study demonstrates a contrast of aerosol properties from biomass burning between near source and long-range transport. | en_US |