The use of a weighing chamber

• Main Authors: Jen-Ying Chen, 陳人滎
• Other Authors: 陳志傑
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/12853356609758514228

碩士 === 國立臺灣大學 === 職業醫學與工業衛生研究所 === 101 === 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.