近年來國內的都市廢棄物焚化廠之戴奧辛排放問題受到大眾關切，為因應大型都市垃圾焚化爐戴奧辛法規的排放標準0.1ng TEQ/Nm3，各廠都進行改善與監測，成效皆相當不錯，因此未來數年大氣中的戴奧辛主要貢獻來源，可能從過去的都市垃圾焚化爐轉移到不確定污染源，如移動性污染源。本研究分別針對隧道內外大氣及汽車管末尾氣進行採樣。採樣分析結果顯示四次隧道內大氣戴奧辛平均濃度為0.49、1.47、0.61、及1.12 pg/m3，而本研究大氣採樣期間(2001年11月至2002年2月)適逢焚化爐停爐改善，四次隧道外大氣戴奧辛平均濃度為0.23、0.53、1.10及0.60 pg/m3，除第三次採樣(2002年1月)外，隧道內大氣戴奧辛平均濃度均高於隧道外測值2-3倍，顯示通過隧道之車輛所排放之戴奧辛濃度在半封閉系統內累積而被採樣器收集。柴油車尾氣採樣結果顯示無轉速(惰轉)與有轉速(40%)濃度測值分別為4.077與0.275 ng/m3，惰轉排放戴奧辛濃度較有轉速排放戴奧辛濃度高出15倍，原因與引擎燃燒效率有關。惰轉時引擎不完全燃燒情況較嚴重，定速運轉時車輛引擎穩定運轉，不完全燃燒現象相對較不明顯，戴奧辛排放濃度也較低，因此對於都市易塞車造成惰轉情況地區需特別注意。汽車排放對大氣戴奧辛濃貢獻量為0.47 g I-TEQ/yr。與其他戴奧辛污染源之貢獻量做比較，顯示汽車排放對大氣戴奧辛貢獻量佔不到1%，貢獻程度不顯著。 Emission of PCDD/Fs from municipal waste incinerators (MWIs) has become a public concern in Taiwan, and a stringent emission standard (0.1 ng-TEQ/ Nm3) of dioxins from large-scale municipal waste incinerators (MWIs) has been promulgated. Since 1998 large-scale MWIs in Taiwan has effectively reduced their dioxin emissions. Therefore, our focus will switch to the mobile sources in future. This study measured PCDD/F concentrations in vehicle exhaust and tunnel air. The PCDD/F concentrations in tunnel air were measured as 0.49、1.47 and 1.12 pg/Nm3, respectively while the PCDD/F concentrations of the air outside the tunnel were 0.23、0.53 and 0.6 pg/Nm3, respectively. The results obtained from these measurements indicated that the tunnel air had higher PCDD/F concentrations compared to the air outside the tunnel. This provides the evidence that PCDD/Fs will be emitted by the vehicles. The PCDD/Fs concentrations in the exhaust emitted from the diesel car used in this study are 4.077 and 0.275 ng/Nm3 when the diesel-engine is idled and operated at 40% of full loading, respectively. The results indicate that the vehicles might emit higher PCDD/Fs concentration in the rush hour during which time vehicles would move at a slower speed or even stand still. The average emission factors obtained from the tunnel study range from 0.0014 to 0.0142 ng I-TEQ/km. Considering the vehicles number and average mileage traveled in Taiwan, PCDD/F emissions ranging from 0.047-0.470 g I-TEQ/yr are obtained for Taiwan. This indicates the vehicles emissions contribute little to the annual total PCDD/F emissions about 180 g I-TEQ/yr in Taiwan. The results presented here are in agreement with the most recent studies.
