- 學位論文
利用石英晶體微天秤監測氣膠相變化
Phase Transition of Aerosols Monitored by Quartz Crystal Microbalance
摘要
氣膠的相態在估算氣膠對於大氣的輻射收支平衡有很明顯的影響，本研究利用高敏感度(0.1 ng)的石英晶體微天平(quartz crystal microbalance, QCM)之共振頻率變化量來量測固態樣品的質量變化，可以觀測樣品潮解前與水之間的吸附作用以及水合物的形成，並利用QCM在液態樣品所造成的頻率變化量與固態樣品不一致，進而決定出樣品因吸濕而轉變相態所需的相對濕度。 本研究利用此技術量測四種單組分無機鹽類(硫酸銨、氯化鈉、氯化鎂，以及硝酸鈣)、兩種內部混和雙組分無機鹽類(氯化鈉-氯化鎂以及氯化鈉-硝酸鈣)、無機鹽類與有機酸類之混合物(硫酸銨-丁二酸)以及2015年4月12日於金門採樣的氣膠樣品之潮解點，並且利用熱力學模式AIOMFAC以及E-AIM Model III計算各個樣品在熱力平衡下之潮解點，並將計算的結果與石英晶體微天平的量測結果作比較。結果顯示單組分的無機鹽類皆呈現一個潮解點，且量測結果與熱力模式計算的結果相近。在雙組分的系統當中，氯化鈉-氯化鎂呈現兩階段的潮解，氯化鈉-硝酸鈣呈現一個階段的潮解，而硫酸銨-丁二酸混合物之潮解點相較於純硫酸銨有下降的趨勢，且潮解後的共振頻率上升比例較純硫酸銨小，說明會潮解的物質占系統中的比例與潮解後的共振頻率上升比例有關係。而金門氣膠樣品的測試結果主要呈現一個潮解點，而此潮解點隨著粒徑的改變與氣膠的組成成份有很大的關係。除此之外，本研究也利用相關的理論去解釋附有氣膠樣品之晶體共振頻率於吸濕過程當中的變化過程。除了能夠量測氣膠的潮解點，此技術也能夠比較氣膠樣品與標準鹽類之量測結果，判斷氣膠樣品當中可能含有的主要成份以及不易潮解的物質的相對多寡，並利用氣膠樣品進行離子層析的結果協助分析其相態變化的過程。 未來希望能利用此技術能夠量測固態樣品質量變化以及相變化的特性，將此技術繼續延伸發展，監測大氣當中的一些化學反應以及可能的物理化學性質。
並列摘要
The physical phase of aerosols can affect the impact of aerosols on the atmosphere radiation budget. A highly sensitive quartz crystal microbalance (QCM) with sensitivity of 0.1 ng was applied to monitor the mass change of solid samples due to the adsorption or desorption processes as the relative humidity (RH) was varied according to the variation of the oscillation frequency of the quartz crystal. With the energy dissipation in the liquid phase different from what happens at solid phase, QCM can also be applied to determine the required RH for the phase transition of the deposited chemical species. In this study, the deliquescence relative humidity, DRH of single-component systems ((NH4)2SO4, NaCl, MgCl2, and Ca(NO3)2), two-component systems (NaCl-MgCl2 , NaCl-Ca(NO3)2 and (NH4)2SO4-succinic acid mixture), and Kinmen aerosols sampled on April 12, 2015 was measured using a QCM. The determined DRHs were compared with the DRHs calculated by thermodynamic models, AIOMFAC and E-AIM. For the single-component inorganic salts, the measured DRHs are consistent with that from thermodynamic models. As to the two-component systems, NaCl-MgCl2 mixture showed two DRHs while NaCl-Ca(NO3)2 mixture had only one significant DRH. The results in (NH4)2SO4-succinic acid mixture showed only one DRH, slightly lower than that of pure (NH4)2SO4. The normalized change of oscillation frequency after deliquescence is associated with the fraction of soluble species ((NH4)2SO4 in this system). As to the field samples (Kinmen aerosols), only one DRH was observed at a given size range of samples. The observed DRH is size-dependent due to the composition variation with droplet size according to the analysis of ion chromatography. Furthermore, this technique may be utilized to monitor the chemical reactions and possible hygroscopic properties (e.g., liquid viscosity) happening in the atmosphere base on the response of QCM investigated in this study.