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都市林對大氣懸浮微粒的淨化效益及i-Tree模式的應用與展望

EFFECTS OF URBAN FORESTS ON PURIFICATION OF ATMOSPHERIC PARTICULATE MATTER AND THE APPLICATION AND PROSPECT OF I-TREE MODEL

摘要


空氣污染隨著都市的發展日益嚴重,而大氣中的懸浮微粒所帶來的危害也備受重視。都市中的樹木藉由植體表面截留微粒物質,普遍被認為具有淨化空氣的效果,然而在量化上由於資料具有高度的不確定性而相當困難。過去在探討懸浮微粒於不同樹種的葉面乾沉降通量上,發展出室內的風洞試驗,以及穿落水或葉片萃洗等現地測量的方法,再透過通量的測定與環境濃度資料的收集,可計算出不同粒徑懸浮微粒於葉面的乾沉降速度,作為未來乾沉降通量的推估或提供模式所需的相關參數。經由整合樹木資料、乾沉降速度、環境資料及經濟效益等發展出的乾沉降模式-i-Tree,是目前世界各國廣泛利用於都市林的生態系服務效益的模擬工具,並可計算出相關的經濟價值。然而,乾沉降模式資料多由國外樹種所建立,若應用於臺灣時,缺乏足夠的可信度,故參數的在地化修正,或現地懸浮微粒乾沉降通量的驗證等,在未來十分重要。透過樹木葉片的截留作用所量化的空氣品質淨化效益,主要經由整體混合層空間內的汙染削減進行計算,但無法定量樹木影響懸浮微粒在大氣中的延散所造成的濃度變化。未來若能整合多個模式,配合實測研究,針對都市林與懸浮微粒的交互作用進行探討,同時驗證都市林樹木對於懸浮微粒的截留,能否實際反映於汙染物濃度的降低,並對人為活動的熱點如公園、街道及遊憩區域等進行汙染物量化探討,可使得我們更瞭解都市林對空氣品質的淨化效益。

關鍵字

延散 乾沉降 截留作用 i-Tree模式 都市林

並列摘要


As the air pollution accompanied by urban development are worsen every year, the adverse effects of particulate matter (PM) on human health has attracted increasing attention. While urban forests are commonly perceived as having the abilities to purify air by intercepting PM with leaves and branches, it is difficult to quantify these purifying abilities due to the fact that factors affecting the interception process is highly variable. Indoor wind tunnel and field experiments, including throughfall or foliage extraction methods, has been developed to determine the dry deposition flux of PM on leaves. These data combined with data that collected PM concentration in the environmental allowed us to calculate local dry deposition velocity of PM, which in turns, were used to establish models of dry deposition. The i-Tree that developed by incorporating tree parameters, speed of dry deposition of PM, environmental conditions, and economic benefits, has been widely adopted to evaluate the benefits, in monetary terms, of ecosystem services of urban forests. However, most dry deposition data was based tree species not endemic to Taiwan, the results obtained by applying these models in Taiwan would not be credible. Therefore, creating and validating parameters sets base on the results of local tree species for i-Tree modeling is extremely important. The benefits of PM purification by urban forests quantified in i-Tree are analyzed based on PM removal through canopy interception within the mixing layer, it is not capable of quantifying the influence of trees on PM dispersion in urban areas. Hence, integrating laboratory investigations, field experiments and modeling of the interactions between urban forests and PM is necessary to better understand the role plants in air pollution control. We propose more research should be conducted to investigate the effect of urban forests in improving air quality in high human-use areas such as sidewalks, parks and recreation areas.

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