| Summary: | 博士 === 國立清華大學 === 化學系 === 91 === Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) are unwanted byproducts from various combustion processes and numerous chemical industrial processes. The toxic 2,3,7,8-substituted PCDD/Fs are lipophilic and tend to accumulate in carbon-rich matrices and in fatty tissues. PCDD/Fs have been detected in every environmental compartment owing to their chemical, physical and biological stability and long-range transport. Moreover, PCDD/Fs emissions from municipal solid waste incinerators (MSWIs) have become a globally environmental issue. Investigation of the relationship between PCDD/Fs level in stack emission from MSWIs and in ambient air, soil and vegetation provides the PCDD/Fs impact on environment from MSWI emissions.
There are six chapters in this thesis. Chapter 1 describes the research motive and purposes. Chapter 2 introduces the methods of PCDD/Fs sampling, PCDD/Fs analysis, ISCST3 model, PCA and HCA statistics. The title of chapter 3 is “Comparative study of monitored levels of PCDD/Fs in ambient air, soil and ISCST3 model predictions in the vicinity of a municipal solid waste incinerator in Hsinchu”. As a result of the newly construction of Hsinchu city MSWI, this study seized a wonderful opportunity to research how PCDD/Fs emission from a new MSWI equipped with modern APCDs could impact the ambient environment. This chapter presents the PCDD/Fs measured in ambient air and in soil around Hsinchu city MSWI during the trial burns in 2000 and compared to those measured in 2001 when it was fully operational. Concentration discrepancies between instrumental quantification and ISCST3 model prediction of ambient air were examined to test the precision and correlation among these two different types of method. Results of PCA, HCA and ISCST3 prediction reveal that Hsinchu city MSWI is not the major PCDD/Fs emission source to the ambient region. Human activities and unknown PCDD/Fs sources may fill up the gap among the model predictions and the instrument measurements. A systematic decrease of PCDD/Fs concentration in the ambient air from the northeast area to southwest was observed. This decreasing trend along the direction of wind is attributed to the heavy industrial activities on the northeast of Hsinchu city and wind flow towards southwest. Higher PCDD/Fs levels in the ambient air were found during spring and lower concentration was observed in summer. We recommend monitoring MSWI on a regional basis where the industrial and human activities are dense as in Taiwan.
The title of chapter 4 is “Distributions and principal sources of PCDD/Fs in ambient air, soil and vegetation in the vicinity of Taichung city and Chiayi city municipal solid waste incinerators together with an arc furnace in Kaohsiung”. Most related researches generally hypothesize a potential emission source at first, and measure the environmental PCDD/Fs levels in simply one or two kinds of matrices to evaluate the influences from targeted source. In this study, PCDD/Fs in four matrices including stack gas, ambient air, soil and vegetation were collected and analyzed from or in the vicinity of Taichung city MSWI, Chiayi city MSWI and one arc furnace in Kaohsiung city, respectively. The main purpose is to investigate the PCDD/Fs distributions in the three areas on the basis of regional viewpoint, and find out the major PCDD/Fs sources in the area. The determination of PCDD/Fs in leaves was carried out using modified and verified USEPA method 1613B. Different type of PCDD/Fs source in the respective investigation areas were proposed: 1. PCDD/Fs in the vicinity of Taichung city MSWI might because of the human activity like the case of Hsinchu MSWI; 2. medical waste incineration was probably the major PCDD/Fs source in the ambient environment of Chiayi city MSWI; 3. the arc furnace was considered one of the principal PCDD/Fs emission source to the surrounding environment in Kaohsiung Lin Hai industrial district. Furthermore, high PCDD/Fs amount occurred in soil resulting in positive correlation between TOC and PCDD/Fs content. It is suggested that banyan leaf could be selected as an atmospheric PCDD/Fs biomonitor in Taiwan.
The title of chapter 5 is “Nationwide PCDD/Fs levels in ambient air, soil and vegetation in Taiwan”. Reported data/results from the existing survey projects and our lab were collected and integrated into the first “Taiwan Environmental PCDD/Fs Database” based on the UNEP guidance document. Taiwan is a small island populated with twenty-two million people in the west living in an area of 36,179 km2. High population density leads different human lives and activities comparative to the continental countries. For the first time, PCDD/Fs levels in ambient air, vegetation and soil around 19 MSWIs and samples from urban areas in Taiwan are discussed and summarized to bring up a nationwide view of dioxin distributions. Typically, correlation between PCDD/Fs levels in ambient air, soil and vegetation was not observed. The MSWIs are therefore not the only or major dioxin emission source. The Mucha MSWI showed clear influence on ambient PCDD/Fs concentrations, i.e. when comparing the previous and currently improved APCDs. Due to short of data, conclusions can not be made between human activity (population or industrial park) distributions and dioxin level distributions in Taiwan. It is suggested regional (county) basis monitoring instead of the measurements simply surrounding MSWIs, and extended to a nationwide monitoring system in the long run.
The title of chapter 6 is “Investigation of meteorological factors influences on PCDD/Fs levels in ambient air using evidences from typhoons”. PCDD/Fs congener concentrations and profile in ambient air under stable weather condition have been proven readily altered by meteorological factors including temperature, wind, rain and air mass origin. However, little has been reported for the atmospheric PCDD/Fs condition right after severe weather variations. This is the first study aiming at the influences of meteorological factors on dioxin congener levels and distributions in ambient air exactly after typhoons. High rainfall and wind speed are both verified to reduce the PCDD/Fs level in ambient air, whereas rainfall influences the most. Relation between rain rate and reduced PCDD/Fs concentration in ambient air samples after typhoons was successfully correlated with an exponential growth curve. High wind speed eliminates the PCDD/Fs concentration in air immediately, but the affect of rain is usually reflected several hours later. PCDD/Fs levels in gaseous phase or particulate phase showed the same trend of variations. It is consequently suggested that both PCDDs and PCDFs in gaseous phase and in particular phase were persistently rose back to their original levels after the typhoon, but rainfall slow down the recovering speed in particulate phase. Severe meteorology factors altered the PCDDs to PCDFs ratio in ambient air, but not the profiles. Moreover, PCDD/Fs level in ambient air would revive in one or two days after the strict weather. These phenomena reveal that atmospheric PCDD/Fs level in Taiwan is not likely to become lower in summer or in autumn due to the prevalence of typhoon in these seasons. A long-term steady weather without heavy rain or high average wind speed is important during atmospheric PCDD/Fs measurement. If time and resources are permitted, chronic ambient air monitoring should be the best strategy to acquire faithful, representative and accurate data.
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