| 摘要: | 近年來，靜電集塵式氣液界面(ESP-ALI)暴露系統已逐漸發展為評估環境中及工業製程等來源之奈米微粒毒性的重要工具之一。一般而言，過去研究主要以球形微粒進行ESP-ALI暴露系統性能之研究。然而大氣中大部分微粒並非完美的球形，且文獻亦指出微粒構形可能影響其收集效率及細胞暴露毒性，例如板狀石墨烯奈米材料常以近乎垂直角度貫穿所暴露之細胞，可能對細胞骨架組織造成物理性傷害。本研究為探討微粒構形對ESP-ALI暴露系統性能之影響，分別以電移動度分析儀(Differential Mobility Analyzer, DMA)篩選出單粒徑之球形蔗糖微粒、非球形奈米黑碳微粒及奈米銀微粒進行ESP-ALI貫穿率實驗，並計算微粒於不同實驗操作條件下之貫穿率或收集效率。同時利用DMA-APM串聯系統即時量測微粒質量，並以碎形維度(Fractal dimension, Df)參數量化奈米氣膠微粒構形。結果顯示微粒通過ESP-ALI暴露系統的貫穿率隨著粒徑下降而下降，並隨施加電壓上升而下降。利用無因次速度比(Vc/Vavg,r)作為轉換參數，細懸浮微粒(dp= 100-250 nm)在不同操作條件下的貫穿率可轉換為高相關性的特徵指數遞減曲線。因此，只要已知微粒的轉換參數值，就可透過此特徵曲線獲得不同帶電量之微粒通過ESP-ALI暴露系統的貫穿率。不同構形之超細懸浮微粒(dp< 100 nm)在ESP-ALI暴露系統中性能相似，但此粒徑範圍下擴散所造成的損失不可忽略。而在細懸浮微的粒徑範圍下，奈米黑碳聚集體(Df= 2.29)的的收集效率高於球形蔗糖微粒。這可能是由於電場和流場分別引起的微粒對準效應於ESP-ALI暴露系統中同時影響不規則奈米黑碳聚集體之運動傳輸行為。此外，本研究進一步提出利用Deutsch理論模式及實驗數據進行擬合所得到的二次曲線，預測不同微粒構形及操作條件下ESP-AL暴露系統的性能。;The electrostatic precipitator air-liquid interface (ESP-ALI) exposure systems were recently developed for assessing the toxicity of atmospheric aerosols and air-borne engineered nanomaterials. Generally, the collection efficiency of ESP-ALI was studied for spherical aerosols. However, atmospheric aerosols are not always perfectly spherical and the particle morphology might affect the ESP-ALI collection efficiency as well as the cell toxicity. For instance, the plate-like graphene nanomaterials penetrate into the cell preferred nearly orthogonal and may physically disrupt the cytoskeletal organization of cells. In this study, to explore the effect of particle morphology on the performance of ESP-ALI, three types of monodisperse aerosols, including spherical sucrose particles, non-spherical soot aggregates and silver aggregates/agglomerates, were selected to evaluate the collection efficiency of ESP-ALI at a flow rate ranging from 0.3 to 1.5 LPM. To quantify particle morphology, the fractal dimension (Df) of testing nano-aerosols were characterized using a tandem system of Differential Mobility Analyzer (DMA, TSI 3081) and Aerosol Particle Mass Analyzer (APM, Kanomax 3601). Results show that at identical conditions, the particle penetrations in ESP-ALI decrease with decreasing particle size and increasing applied voltage. The penetration for fine particles (dp= 100-250 nm) under different operating conditions can be well correlated by a characteristic exponential curve using a dimensionless drift velocity (Vc/Vavg,r) as the scaling parameter. It suggests that the performance of the ESP-ALI can be predicted as long as the value of Vc/Vavg,r was known. For UFPs (dp< 100 nm) with different particle morphologies, the particle penetrations in ESP-ALI are similar, but their diffusion losses are not negligible. In contrast, for fine particles, the collection efficiency of soot nano-aggregates (Df= 2.29) is higher than that of spherical sucrose particles. This might be due to the simultaneous influences of the electric-field-induced alignment and the flow-field-induced alignment. Furthermore, based on the Zhibin and Guoquan (1994)’s Deutsch model [1], a quadratic equation was applied to fit the experimental data and be used to predict the performance of the ESP-ALI. |
