本研究利用ISCST3空品擴散模式對台灣地區周界大氣戴奧辛之擴散、傳輸及沉降之情形進行模擬，配合實際量測周界大氣戴奧辛之數據比對，了解ISCST3模式模擬台灣周界大氣戴奧辛濃度與沉降之適用性。研究結果顯示實際量測周界大氣戴奧辛濃度受大氣中PM10濃度及降雨量變化之影響，模擬周界大氣戴奧辛濃度同樣受大氣中PM10濃度及降雨量之影響。此外，模擬周界大氣戴奧辛濃度亦受混合層高度變化之影響，導致周界大氣戴奧辛濃度實際量測值及模擬值之間的差異。在沉降通量方面，不論是實際量測值或模擬值濕沉降通量都與降雨頻率趨勢呈負相關性變化。實際量測乾沉降通量趨勢受周界大氣戴奧辛濃度與沉降速度相互交叉影響，而模擬乾沉降通量僅受模擬周界大氣戴奧辛濃度值影響。實際量測總沉降通量受大氣中粒狀物粒徑分佈比率之影響，總沉降通量受乾、濕沉降通量交互變化之影響。模擬總沉降通量受ISCST3模式參數限制，無法任意隨大氣中粒徑分佈比率變化而更改模擬總沉降通量之趨勢，導致總沉降通量模擬值與實際量測值之間的差異。文獻指出隨著模擬範圍擴大，模式低估之情形越嚴重，本研究模擬範圍超出模式限制50 km，模擬濃度值雖有10~70倍不等之低估情況，但模擬值與實際量測值趨勢類似，表示以ISCST3模擬長期及長程周界大氣中戴奧辛之濃度及沉降有相當之可信度。最後，以ISCST3模擬北部空品區、中部空品區及雲嘉南空品區內主要貢獻汙染源，結果顯示北部空品區及中部空品區之主要貢獻源為鋼鐵廠，雲嘉南空品區之主要貢獻源為都市垃圾焚化爐。成為主要貢獻源之原因並非單純以排放量作判定，視汙染源是否位於該區域主要風向之上風處位置而定。 Industrial Source Complex Short Term (ISCST3) model has been used to simulate air pollutant concentrations and depositions in ambient air. In this study, long-term concentrations and depositions of dioxins are simulated and compared with the long-term measurement results. Measured and simulated dioxin concentrations are directly influenced by PM10 concentration. Additionally, simulated dioxin concentrations are also affected by mixing height. Therefore, simulated dioxin concentrations do not match well with measured dioxin concentrations in ambient air. As far as the deposition flux is concerned, both simulated and measured wet deposition fluxes are inversely correlated with precipitation frequency. Simulated dry deposition flux is mainly affected by ambient dioxin concentrations. In fact, dry deposition flux depends on ambient air concentration and settling velocity. Furthermore, the total dioxin deposition flux measured is affected by the particle size distribution of ambient particles. Simulated total dioxin deposition flux is limited by particle size distribution and it is difficult to separate the effect of dry and wet deposition flux individually. Simulated results tend to underestimate as the distance is increased. In this study, dioxin concentrations and depositions in ambient air are simulated for the range greater than the model limit. Although simulated values underestimate the measured values by 10 to 70 times, the simulation trends match well with measurement trends. It means ISCST3 model can simulate dioxin concentrations and depositions well. Finally, ISCST3 model is used to simulate the main contributing point sources in the area. Major contributing point sources are always located at upwind, but not necessary to be the ones with the largest emission rates.
