一個電子式多階衝擊器的開發

Abstract

多階衝擊器經常被應用於測量微粒的質量分佈，但是微粒濃度會隨著氣象及污染源的變化而改變。傳統的多階衝擊器皆為手動採樣，只能量測日平均濃度，無法有效地掌握污染物逐時的變化，因此若要有效的掌控汙染源的排放，勢必需要一套能夠即時偵測大氣或煙道質量濃度變化的設備。 本研究以交通大學微孔多階衝擊器(NCTU Micro-Orifice Cascade Impactor, NMCI)為基礎進行外殼上的改良，並在上端連接自製單極充電器 (unipolar charger)，將微粒帶電後進入衝擊器中，使得衝擊板所收集到的電流訊號可藉由微電流計量測，並經由公式轉換為數目濃度及質量濃度。此電子式微孔多階衝擊器在本研究中稱為EMCI (Electrical Micro-Orifice Cascade Impactor)。因配合單極充電器則將原先操作流量30 L/min調整為16.7 L/min，並量測其EMCI收集效率曲線其結果與NMCI相近。此外也針對終端濾紙階層進行改良，電流值在10-900 fA之間其EM-K讀值皆低於AE讀值，其低估值介於0-15%之間。接著量測微粒收集效率曲線並與MOUDI進行比對，由結果顯示微粒收集效率曲線其結果與MOUDI相當接近，使用EM-K時量測粒徑小於1 m其結果與MOUDI相當接近，但是量測大於1 m時其結果皆有高估的情形。最後利用SMPS比對EMCI及ELPI+，由結果發現數目中間粒徑的部分，SMPS與EMCI將當接近，ELPI則較為低估，數目濃度的部分在較低濃度(>2.0 x 105 #/cm3)的測量時其EMCI及ELPI+數目濃度皆與SMPS所量測的數目濃度相近，但是在較高濃度(3.0 x 106 #/cm3)時其EMCI及ELPI+所量測的數目濃度皆低於SMPS。

The micro-orifice cascade impactor is used to measure the mass distribution of the particulate matter (PM). The micro-orifice cascade impactor that is used to sample the PM is manual sampling for 24-h average concentration. The hourly concentration could not be measured effectively. In order to understand the sources emission, the real-time measured instrument must be developed in the future. In this study, the NCTU Micro-Orifice Cascade Impactor (NMCI) is used to modify. Base on the NCMI, the hand-made unipolar charge is put on the upper NCMI. The PM would be charged and flow into the impactor so that the current signal would be measured. The signal will be transform to numerical concentration and mass concentration by the equation. This impactor which is called Electrical Micro-Orifice Cascade Impactor (EMCI) in this study. The operation flowrate is changed from 30 L/min to 16.7 L/min and the collection efficiency curve is closed to NMCI. On the other hand, the after-filter was also modified. The EM-K value is less than AE value when the current value is between 10 and 900 fA, and the underestimate value is about 0-15 %. The collection efficiency curve is also compared to MOUDI. When the PM size < 1 μm, the result of the EM-K and MOUDI are similar. When the PM size > 1 μm, the result of the EM-K and MOUDI was overestimated. The comparison of the size between SMPS, EMCI and ELPI+, ELPI would be underestimated. The lower numerical concentration (>2.0 x 105 #/cm3), both of the EMCI and ELPI are similar with SMPS. When the higher numerical concentration (<3.0 x 105 #/cm3), both of EMCI and ELPI are less than SMPS.