- 學位論文
北台灣大氣環境中戴奧辛之 北台灣大氣環境中戴奧辛之乾、濕沈降特性研究
Evaluation of Dry/Wet Deposition of PCDD/Fs in Northern Taiwan via Automated and Traditional Samplers
摘要
燃燒程序排放至大氣中的戴奧辛於大氣擴散過程中會落至水體或民眾生活環境中，造成對人體健康之直接或間接影響。戴奧辛屬高沸點物質於環境中大量存在固相上，因此大氣中的粒狀物即成為戴奧辛自煙囪排放後的主要傳輸介質，所以監測落塵亦可間接得知戴奧辛影響水體環境及民眾健康的程度。 本研究利用新型落塵採樣器(Automated sampler)以北台灣地區為採樣背景，同時搭配傳統型落塵採樣器(Traditional sampler)進行大氣落塵採樣，一方面可精確得知沈降通量，另一方面也可瞭解傳統採樣器所存在的採樣問題及影響因素，並且探討不同沈降方式對戴奧辛沈降通量變化的影響。同時求出採樣期間戴奧辛沈降速度與雨除係數，藉以得知北台灣地區戴奧辛落至受體表面之速率以及降雨對於懸浮於大氣中的戴奧辛去除量。 傳統型落塵採樣器所得結果顯示戴奧辛沈降量為54-220 pg/m2-day (2.0-9.9 pg TEQ/m2-day)，而Automated sampler採樣所得之沈降量239-490 pg/m2-day (15.0-25.8 pg TEQ/m2-day)。有無即時收樣系統避免光解是兩種採樣器最大不同處，具有即時收樣系統的Automated sampler所得之沈降通量大於傳統沈降採樣器所得之沈降通量。將兩種採樣器所得之沈降通量做一差異百分比可得知，總差異百分比與大氣溫度變化成正相關性，物種差異則是PCDD/Fs鍵結氯數越低，差異百分比越大，由此可知新型落塵採樣器較傳統型落塵採樣器更能準確採集戴奧辛沈降通量。此外，本研究也進行乾、濕沈降對戴奧辛沈降通量變化之影響，將乾、濕沈降各別實際採樣時間、雨量與降雨時數加入探討時，每一月份濕沈降通量皆高於乾沈降通量，乾沈降通量約149-224 pg/m2-sunny day (11.1-16.5 pg I-TEQ/m2-sunny day)，濕沈降通量約690-10100 pg/m2-rainy day (36.8-228 pg I-TEQ/m2-rainy day)。另外，將乾、濕沈降通量與週界戴奧辛濃度經交叉計算後得平均沈降速度約0.26 cm/s，雨除係數則為1.4×105。
並列摘要
PCDD/Fs emitted to atmosphere may eventually fall to water body or environment during atmospheric diffusion and impact human health. Dioxin is a substance of high boiling point and is adsorbed enormously on the solid phase in environment and the particles become its main transportation media. Therefore, monitoring the atmospheric deposition of particles may provide the information regarding the extent of its PCDD/F effects on water body and people’s health. This study focuses on the understanding of the dry/wet deposition of PCDD/Fs in northern Taiwan via automated and traditional samplers. The main advantages of this method include: (1) obtaining more accurate data regarding deposition flux of PCDD/Fs from atmosphere to land; (2) the combination of two types of samplers can help to clarify the possible under-estimation of deposition flux achieved with the traditional samplers. In addition, the deposition velocity and scavenging ratio during sampling process are also calculated so that we may find out how efficient PCDD/Fs falls on to the surface receptor in northern Taiwan and the removal efficiency of PCDD/Fs while raining. The deposition flux of PCDD/Fs collected by traditional sampler ranged from 54- 220 pg/m2-day (2.0-9.9 pg TEQ/m2-day), while the deposition flux of PCDD/Fs collected by automated sampler was much higher, ranging from 239-490 pg/m2-day (15.0-25.8 pg TEQ/m2-day). Furthermore, the relative difference of PCDD/F deposition flux between the measurement of automated and traditional samplers increased with increasing atmospheric temperature. It is also interesting to find the relative difference of lowly chlorinated PCDD/Fs were higher than that of highly chlorinated PCDD/Fs. This study also investigates the influences of dry/wet deposition on sampling time and rainfall. The results indicate that wet deposition flux was higher than dry deposition flux. Dry deposition flux was measured as 149-224 pg/m2-sunny day (11.1-16.5 pg TEQ/m2-sunny day) while wet deposition flux was 690-10100 pg/m2-rainy day (36.8-228 pg TEQ/m2-rainy day). As indicated by this finding, wet deposition can remove PCDD/Fs in a more significant way than dry deposition. Furthermore, the average PCDD/Fs deposition velocity and scavenging ratio in northern Taiwan are calculated as 0.26 cm/s and is 1.4×105, respectively.
參考文獻
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