摘要
在環境與職業衛生領域，粒狀污染物 (Particulate Matter, PM) 漸受重視，且關注的粒狀汙染物粒徑由PM10 轉向粒徑較小的PM2.5，因微粒粒徑小，經濾紙採樣後質量輕，更顯現出微量質量分析精準度之重要。粒狀污染物之質量分析主要以濾紙捕集微粒後再使用天平進行微量分析，由於易受到環境溫溼度及靜電荷等因子干擾，使得微量分析結果產生偏差。其中最常被探討的就是相對溼度之影響，由於秤重環境之溼度控制相對不易，因此本研究建置一天平秤重艙，藉由氯化鎂飽和溶液維持固定蒸汽壓下，提供穩定相對溼度，溫度控制透過天平室內空調與秤重艙進行熱交換後達溫度平衡，此外將濾紙放置於天平秤盤上以Am241去除靜電使得濾紙趨近於電中性，可排除靜電荷對秤重結果精準度的影響。根據長時間對天平秤重艙的監測結果顯示，此一控制方式可使系統保持溫度為18–21℃及相對溼度為31–35%，顯示天平秤重艙是一有效且可行的設備。此外，秤重艙的使用者必須戴手套並調高系統內氣體流率，避免手部水氣破壞系統內穩定相對溼度。待調理濾紙需分裝於儲存盒後開蓋調理，亦或者選擇厚度較薄的濾紙，可加快調理時間。空白與負載微粒之濾紙，在調理與微量分析時暴露於高相對溼度環境 (RH: 75%) 下，空白MCE濾紙有0.5mg質量上升，倘若負載0.5 mg氯化鈉微粒，質量會高估1.2 mg。使用本研究之天平秤重艙控制秤重及調理環境相對溼度在31–35 %，並遵照建議之靜電消除方式，對於一般常用37-mm濾紙負載微粒之微量分析，其質量偵測極限可達到3μg以下。
並列摘要
A reliable gravimetric analysis of particulate matter filters is of great importance in exposure and risk assessment in industrial hygiene and/or environmental health, especially for those fine particles with light weight like PM2.5. Weighing bias may be caused by a number of environmental and operating factors. Among these factors, the humidity effect is the mostly addressed one. This study proposed a cost-effective weighing chamber with humidity control by the use of saturated magnesium chloride solution to meet the USEPA requirements for filter weighing. To exclude the interference of electrostatic charges, filter samples were treated with a radioactive source Am241 on the microbalance pan during weighing. Long term monitoring showed that the relative humidity inside the weighing chamber were between 31–35 % while the temperature were between 18–21 ℃. The air pressure inside the weighing chamber was kept slightly positive by adjusting the supply air of humidity control unit at 15 L/min during filter conditioning and 25 L/min during filter weighing to maintain a stable humidity condition and prevent aerosol contamination from outside. Moreover, the operator should wear gloves to prevent hand moisture evaporation. Filter samples were suggested to be stored and conditioned in the weighing chamber with the filter holder’s lid opened to expedite and enhance the filter conditioning. When a hygroscopic filter, such as MCE, was used to collect 0.5 mg hygroscopic NaCl particles, a mass increased of 0.5 mg was due to the filter, and additional 1.2 mg mass due to collected NaCl particles, which the weighing was performed under RH 75 %, rather than in the weighing chamber. With the use of the weighing chamber and the recommended practices, this study demonstrated an excellent weighing quality and the mass determination limits were below 3 μg for 37-mm particle-laden filter samples commonly encountered in practical situations.