與來源粒徑分布一致的非聚集狀微塑膠粒之氣膠化技術

Abstract

近年來，微塑膠在空氣中的廣泛檢出及其對人體健康潛在風險，逐漸在各界引起高度的關注。為了從最基礎的層面深入探討微塑膠吸入暴露對健康的影響，並推動相關採樣分析方法的開發與性能評估，亟需建立一套具備粒徑控制精準、濃度穩定且再現性高的微塑膠產生系統，作為後續研究的關鍵基礎。然而，目前文獻報導的微塑膠產生系統，無論在顆粒粒徑還原度或產出穩定性方面，仍存在改進空間，尤其在長時間穩定產生較大粒徑微塑膠氣膠環境時，更顯不足。

本研究以超音波霧化技術為核心，結合懸浮液輸送與控制系統，建構一套可調控微粒粒徑與濃度的微塑膠氣膠產生器，最大可產生直徑達10 µm的微粒，並系統性評估各項操作參數，包括：攪拌方式、針筒擺放角度、懸浮液濃度與粒徑、界面活性劑添加比例等，對微塑膠粒在氣膠化後的濃度與粒徑分布的影響。為確保懸浮液在產生過程中維持均勻分散，本研究針對攪拌子體積與磁石攪拌器轉速等條件進行探討，並以攪拌子體積與轉速的乘積為指標，針對不同針筒容量，提出可以維持長時間穩定輸出懸浮液的操作條件。

研究結果顯示，針筒垂直擺放並搭配持續磁力攪拌可有效減少沉降，確保長時間產出穩定濃度的微塑膠氣膠。當懸浮液的體積濃度越高時，雖然產生微塑膠氣膠的濃度也會越高，但由多個單顆粒所形成之氣膠微粒的比例也會跟著增加，以致於造成整體粒徑分布的偏移。因此，如果以產生單分散微塑膠為目的，懸浮液的體積濃度會有可操作的濃度上限，而且該上限值大小會隨著微塑膠顆粒的直徑減小而降低。以PMMA顆粒為例，當粒徑為0.8 µm時，懸浮液的體積濃度必須低於0.005%，才能避免由微粒氣動直徑分析儀(APS)觀測出明顯的粒徑分布偏移。相較之下，3 µm顆粒的可操作濃度上限，則可增加約0.1%。而5 µm PMMA的操作濃度上限則以不超過1%為原則。當懸浮液推進流率為0.1 ml/min時，5 µm PMMA的氣膠質量濃度最高約14.75 mg/m³，其中約有75%的氣膠數目是以單顆粒的狀態存在，而整個產生過程所造成的PMMA的質量損失約為5%。雖然，所產生的質量濃度可以進一步藉著增加懸浮液的推進流率來提升，但由於液滴無法完全乾燥的限制，現階段的推進流率上限設定為0.2 ml/min。除此之外，實驗結果顯示，界面活性劑對PMMA氣膠生成效率與長時間穩定性並未產生明顯的助益。於是在操作簡便性及成分單一性等因素的考量之下，不建議在本系統中使用。

整體而言，本研究成功建立一套可長時間穩定供應與微塑膠粉末粒徑分布相符合的氣膠產生系統，未來可應用於微塑膠暴露模擬、吸入毒理試驗以及相關氣膠研究。

In recent years, the widespread detection of microplastics in the atmosphere and their potential health risks to the human respiratory system have drawn increasing attention. To investigate the health impacts of inhaled microplastics from a fundamental perspective and to support the development and performance evaluation of sampling and analytical methods, it is essential to establish a microplastic aerosol generation system with precise particle size control, stable output concentration, and high reproducibility. However, current literature reveals that existing systems still face limitations in terms of size distribution fidelity and long-term output stability, particularly in generating stable aerosols containing larger-sized microplastic particles over extended durations.

This study developed a controllable microplastic aerosol generator based on ultrasonic nebulization technology, integrated with a suspension delivery and control system. The system is capable of producing dry and stable particles with aerodynamic diameters up to 10 µm. A comprehensive evaluation was conducted to examine the influence of various operational parameters—including stirring method, syringe orientation, suspension concentration and particle size, and surfactant addition—on the resulting aerosol particle size distribution and concentration. To ensure homogeneous dispersion of the suspension throughout the generation process, factors such as stir bar volume and magnetic stirrer speed were investigated. A dimensionless parameter (the product of stir bar volume and rotation speed) was used to determine suitable operating conditions for different syringe capacities to achieve stable and consistent suspension delivery.

Results demonstrated that vertical syringe placement combined with continuous magnetic stirring effectively minimized particle sedimentation, allowing stable aerosol output over a 13-hour test period. Higher suspension concentrations led to increased aerosol mass concentrations, but also raised the fraction of agglomerated particles, thereby shifting the overall size distribution. Consequently, when generating monodisperse aerosols, the suspension concentration must remain below a threshold, which decreases with smaller particle diameters. For example, PMMA particles with a diameter of 0.8 µm required a volume concentration below 0.005% to avoid significant distribution shifts observed by an Aerodynamic Particle Sizer (APS). In contrast, the operational limit increased to approximately 0.1% for 3 µm particles and up to 1% for 5 µm particles. Under a suspension feed rate of 0.1 mL/min, 5 µm PMMA particles yielded a maximum aerosol mass concentration of 14.75 mg/m³, with about 75% of particles remaining as singlets. The overall particle loss during generation was within 5%. Although higher aerosol concentrations could be achieved by increasing the feed rate, incomplete droplet drying imposed an upper limit of 0.2 mL/min under current conditions. Additionally, the use of surfactants did not significantly enhance aerosolization efficiency or long-term stability for PMMA particles; therefore, their use is not recommended to maintain operational simplicity and chemical consistency.

In summary, this study successfully established a microplastic aerosol generation system capable of long-term stable output and particle size distribution fidelity. The system provides a robust platform for future applications in microplastic exposure simulation, inhalation toxicology, and related aerosol research.