微粒分徑採樣器研究

Abstract

第一章:許多研究指出微粒的粒徑對健康有著不可忽視的重要性，因此微粒分徑採樣愈顯的重要。目前各國正努力監控大氣中細懸浮微粒濃度，目前最常見BGI所生產的VSCC (Very Sharp Cut Cyclone)旋風採樣器。已有研究報告指出，分徑採樣器會受微粒沈積效應而改變分徑效果，本研究針對微粒的負載特性做一系統性的探討，如微粒大小、分徑器大小、微粒種類、環境濕度並研析改善微粒負載造成的負面效應。 本研究以VSCC構型為基礎，做不同尺寸縮放，設計四款旋風分徑採樣器(主體幹直徑分別為13.0-35.6 mm，透過不同大小的旋風分徑器，觀察負載效應對其分徑性能的影響。本實驗的測試微粒為酒石酸鉀鈉（PST）、癸二酸二辛脂(DEHS)、氯化鈉(NaCl)水溶液，經由超音波霧化器產生微粒，接著通過輻射源經帶電中和處理。主要監測儀器為氣動微粒分析儀(APS)，分別量測分徑器入口處與出口處之微粒濃度與粒徑分布，並據以計算其微粒穿透率曲線。 測試結果顯示，在使用固態微粒PST做為測試粒徑時會有嚴重的負載效應；當等比例放大縮小分徑採樣器，對於負載效應的結果彼此間並無明顯差異。在負載測試開始20分鐘內2.5 μm穿透率由在採樣一開始時會由50%快速下降至30%。因此微粒的負載效應會造成低估採樣濃度，微粒負載是一極為複雜的過程，微粒粒徑分布、微粒表面特性、測試環境的溫濕度均會造成負載特性的改變。 第二章:大氣中空氣污染物進入的人體的主要途徑是透過呼吸運動。為了評估粒狀汙染物的健康危害，需要針對微粒進行分徑探討，因為不同氣動直徑的顆粒可能沉積在人體呼吸道的不同部位而造成不同程度的健康危害。研究表明，大多數用於職業衛生採樣的個人分徑器50 %截取粒徑於4 μm，但目前仍沒有採樣器能符合國際ACGIH / ISO / CEN /標準的斜率。同時市面上的採樣器都存著微粒負載效應，這會導致採樣器的分離效率曲線隨著採樣的進行而轉移到較小的粒徑。然而負載效應的解決方案之一是虛擬旋風分徑器，虛擬旋風分徑器是一構造簡單、輕便的分徑採樣器。微粒進入分徑器中常被歸類為形成競爭旋流（vortices）的反旋風器（anticyclone），是一種非直接接觸內壁或衝擊板的氣膠分徑裝置。目前已有研究將二維的氣膠運動特性流場模擬(Torczynski and Rader 1997)。但是針對其內部流場氣流三維的走向的研究仍不足。(Chen et al. 1999)等人的研究則將虛擬旋風分徑器設計使用於個人分徑採樣器，但是由過去的資料顯示，其分徑原理其對於較大粒徑微粒的捕集效率稍有不足，大微粒的穿透率明顯高於國際標準可呼吸性粉塵曲線，同時目前虛擬旋風分徑器多被使用在個人分徑採樣，仍無使用於大氣採樣之虛擬旋風分徑器。 實驗系統主要可分成微粒產生與微粒量測兩個部份。微粒的產生主要是利用注射泵浦（syringe pump）將特定濃度的酒石酸鉀納(PotassiumSodium Tartrate Tetrahydrate, PST, Wako PureChemicalIndustries,Ltd.）溶液輸送至超音波霧化噴嘴後，送入的液體經過超音波的震盪而破碎成許多微小的液滴，待稀釋、乾燥後，即為所需的測試用氣懸微粒。微粒特性之測量則利用氣動直徑分析儀(Aerodynamic Particle Counter, Model APS 3321, TSI Inc., USA) 進行量測。虛擬旋風器分徑性能的主要操作參數包括，曲率半徑、離心氣旋腔長度、寬度、高度、出入口高度R、L、W、H、w (mm)。 結果表明，當氣流通過虛擬旋風分徑器時，受到兩側邊界層的影響部分氣流的流速變慢大微粒的移動速度下降，降低了微粒慣性力的表現，因此而部分微粒會循著氣流現離開虛擬旋風分徑器。為了減少這種現象，我們設計了不同長度的VC。為觀察VC增加離心氣旋腔長度與穿透曲線的關係，當長度增加至20 mm時可以有效增加大微粒的捕集效率。虛擬旋風分徑器長度控制在20 mm，並且改變了VC的曲率半徑（R），高度（H）和寬度（W）。結果顯示高度與長度可縮減至10 mm，同時亦可符合ISO的可呼吸性粉塵曲線。基於以上結果最終構型長度高度寬度則是定於20、10、10 mm。最後為設計不同流量進出口高度設計為0.35〜1.2 mm，調節流量5.5〜21.5 L / min，性能相同。本研究設計了一系列可提供不同流率5.5到21.5 L/min提供選擇、並具有相同分徑效率、無負載效應可用於長時間採樣、同時可以符合國際標準曲線的虛擬旋風器。 關鍵字：虛擬旋風分徑器、個人分徑採樣器、可呼吸性粉塵 第三章: 職業衛生依照微粒沉積在呼吸道不同位置的分徑準則，以及環境分徑採用US-EPA訂定的PM10與PM2.5分徑標準曲線。理論上，PM2.5應該全數屬於PM10的一部份，但是嚴格檢視US-EPA兩者曲線的定義發現，當微粒粒徑小於1.6 μm，PM2.5會大於PM10，同時反觀美國環保署 (US-EPA) 雖然公告了PM2.5分徑曲線的數值，但目前仍沒有公認的公式能夠描述其曲線，因此，我們欲參照Soderholm在所提出的可吸入性粉塵公式SI(d)= 0.5(1+e-0.06d) %的方式，找出最佳解來模擬PM2.5的分徑曲線。相對地；同時由於美國環保署在制訂PM2.5的環境標準時，並不全然以健康效應為考量，有部分是根據量測結果發現，大氣中的微粒會依照不同的來源(產生方式)有不同的粒徑分布，根據文獻指出，構成粗粒峰的微粒大多是透過天然方式產生，如:地殼元素、海鹽、生物性微粒；相對地，含碳、重金屬、有機物等與人為活動相關的微粒成分大多集中在累積峰。換句話說，為針對不同的污染來源進行區分，將會根據上述的發展趨勢，提出PM1.0及PM0.1的分徑建議標準。因此，第三階段則是將以職業衛生分徑曲線模式(Soderholm, 1989)為基礎，並為US-EPA所公布PM10、PM2.5分徑曲線數據找到合適的數學模式，接著將更進一步嘗試根據實驗數據與數學模式提出實務可行的PM1.0或PM0.1的分徑建議。 關鍵字:虛擬旋風分徑器、旋風分徑器、國際標準曲線。

第一章:Increasing attention has been drawn to the adverse health effects of particulate matter less than 2.5 μm (PM2.5) over the past several decades. To obtain reliable PM2.5 measurements, it is critical to efficiently separate particulate matter less than 2.5 μm in the airstream from the beginning to the end of sampling. However, commonly used separators for PM2.5 monitoring, such as the BGI Very Sharp Cut Cyclone (VSCC), are usually subject to aerosol loading effects. This study investigates the loading effect on cyclone separation performance as a function of particle size, cyclone size, particle material, and air humidity. Based on the ratios of dimensions to the body diameter of the BGI VSCC, four cyclones with different body diameters (13-35.6 mm) are fabricated. An ultrasonic atomizer is employed to generate micrometer-sized potassium sodium tartrate (PST) particles and sodium chloride (NaCl) particles as solid challenge particles and di-ethyl-hexyl-sebacate (DEHS) particles as liquid ones. Aerosol particles are neutralized to the Boltzmann charge equilibrium. An aerodynamic particle sizer measures the aerosol distributions and number concentrations upstream and downstream of the cyclones. The experimental results show that solid particles such as PST with sizes close to the cyclone cut-point exhibit a significant loading effect. However, no significant difference is found on aerosol loading effect on for different-sized cyclones. The cyclone separation curve appears to shift toward smaller sizes due to aerosol loading. During the loading test, the aerosol penetration of 2.5-μm particles abruptly decreased, from 50%, at the first 20 minutes to a relatively stable level of 30%, an average decrease of 20%. Thus the performance of cyclone PM2.5 samplers with progressive aerosol loading might result in an underestimation of PM2.5, particularly for continuous monitoring of particulate matter Key words : cyclone, loading effect, penetration 第二章:Inhalation is the most significant route of entry for airborne pollutants in the atmosphere. To evaluate the health hazard of airborne particulates, size-selective sampling is obviously needed, as particles of different aerodynamic diameters might deposit on different parts of the human respiratory tract. Previous studies have shown that most of these samplers can meet the 50% cut-point by adjusting to the right sampling flow, but not the slope of the international ACGIH/ISO/CEN/ respirable convention. Most of the currently commercially available samplers suffer from aerosol loading effect, which causes the separation efficiency curve of the samplers to shift to smaller aerosol size as sampling proceeds. One of the solution to loading effect is the virtual cyclone, also referred to as anticyclone, which employs nonimpact aerosol separation, that offers several advantages over more traditional impact-based particle separation. An ultrasonic atomizer was used to generate micro-meter-sized PST (potassium sodium tar-trate tetrahydrate) particles as solid challenge aerosols. A syringe pump delivered the PST solution to the ultrasonic atomizer to generate challenge particle. A Am-241 radioactive source was used to neutralize the particles to the Boltzmann charge equilibrium. An aerodynamic particle sizer (APS, Model 3321, TSI Inc., St. Paul, MN, USA) was used to measure the particle size distributions and number concentrations upstream and downstream. The dimensions of the virtual cyclone were changed to sort out the best configurations that best fit to the ISO respirable convention. The major dimemsions varied included the width of inlet and outlet, the height of inlet and outlet, and the size of recirculation chamber. The defect of high aerosol penetration on the large particle size was eliminated by increasing the inlet width and at the same time, the outlet width. It was found that as the inlet width in-creased from the original 5 mm to 20 mm, the aerosol penetration curve lowered to match with the ISO respirable convention. The size of the recirculation chamber showed no effect on the aerosol penetration pattern. However, the aerosol loading capacity increased with recirculation chamber size, as expected. The final design of the virtual cyclone has an inlet width of 20 mm, in order to make the whole sampling train miniaturized and handy to use in the field. The sampling flow of the new virtual cyclone can be increased from 5.5 to 21.5 L/min, as the inlet and outlet height increased from 0.35 to 1.2 mm, with on shift on the overall aerosol penetration curves. A series of new virtual cyclone samplers are developed. These samplers have perfect match to the international ISO respirable convention, and show constant operation, i.e., no aerosol loading effect, because aerosol deposition was spread out to the whole recirculation chamber. Key words :Virtual cyclone, personal sampler, respirable convention

第三章:The collective efficiency of samplers and the deposition place were affected by the characteristics of particles and different sizes. The development of standards was inevitable and necessary trend in the future. There are two major categories of sampling standards which were occupational and environmental. Although the sizing and sampling criteria for occupational hygiene have a definite numerical model, this model does not incorporate Asian respiratory particle deposition data. On the other hand, the US-EPA's guidelines for the sizing of PM10 and PM2.5 are published, and there is still no recognized formula. Although US-EPA has relevant verification rules for the performance of the sizing sampler, it is based on experiments. In order to improve the standards of US-EPA PM2.5 which were higher than PM10 at small particle size, the model from Soderholm were used in this study. Depended on these criteria, the size-selective samplers were developed. There are three types of samplers based on different 50% cut off size were wildly used in occupational hygiene. The types which commonly used were respirable samplers. Virtual cyclone (VC) could fit the respirable criteria , and which also didn’t have loading effect. The next parts were environmental sampling curves which compared with the criteria, the model and the penetration curves of samplers. Each model were discussed about PM10, PM2.5, PM1.0, PM0.1, PM0.004.The corresponding samplers were developed .Except for VC each one had loading effect after a long time sampling.