| 摘要: | I 氣膠含水特性在氣膠質量濃度量測、酸性沉降、雲霧形成機制、能見 度衰減、氣候變遷與人體健康的議題中皆佔有顯著的影響地位。本研究以 Lee and Hsu (1998)所發展的EA-TCD 氣膠含水量量測系統為基礎，使用氣 相層析儀(GC)搭配熱導電偵測器(TCD)量測收集氣膠含水量。 以GC-TCD法量測25℃下NaCl、Na2SO4、NH4NO3、(NH4)2SO4與NH4Cl 純鹽類氣膠在相對溼度介於20%至90%間的增濕與降濕狀態下的含水量， 本方法的精密度在±3%以內，此外GC-TCD 法與其他文獻量測結果的差異 百分比與平均誤差分別小於±6%與±5%，顯示本方法可適用於無機氣膠含水 特性的量測。在本文中， 以純鹽類氣膠含水特性量測結果評估 ISORROPIA、AIM2 與GFEMN 熱力平衡模式的含水特性推估結果，結果 顯示ISORROPIA 熱力平衡模式可準確推估大多數無機性純鹽類氣膠的含 水特性，最適合使用於混合氣膠含水特性的探討。各種混合莫耳比下的 NaCl-Na2SO4 與NH4NO3-NH4Cl 雙鹽類混合氣膠系統的共同潮解相對溼度 (MDRH) 分別為74% 與54% ； 本文對於NaCl-Na2SO4-NaNO3 與 NaCl-(NH4)2SO4-NH4NO3 三種鹽類混合氣膠的MDRH量測結果分別為70% 與50%；在混合氣膠系統中的完全潮解相對溼度量測結果則顯示出與原始 氣膠組成有關。NH4NO3 氣膠潮解相對溼度(DRH)與周圍溫度為反比的關 II 係，可由DRH 在15、25 與35℃下分別為68、62 與54%的量測結果加以 證實。 本文首次展現Na2CO3氣膠含水特性的量測數據，其DRH 與再結晶點 相對溼度分別為78%與39%。此外，NaCl-Na2SO4雙鹽類混合氣膠系統內的 eutonic 混合鹽組成，本文提出第一次的量測數據以說明eutonic 混合鹽組成 應逼近於含有90%的NaCl 與10%的Na2SO4。至目前為止，文獻對於氣膠 含水特性複雜的三種鹽類混合氣膠僅有非常稀少的量測數據，本文不僅可 以提供不同物種組成與混合比例的三種鹽類混合氣膠含水特性的量測結 果，並探討量測結果與模式推估結果的差異性，有助於瞭解此種混合氣膠 系統的含水特性。最後，本文應用GC-TCD 法量測大氣氣膠的含水特性， 顯示在相對溼度介於62 至77%之間，氣膠含水量在大氣細粒徑氣膠的質量 組成中約佔有19 至41%的比例。 III Abstract Hygroscopic aerosols play a significant role in atmospheric phenomena such as aerosol mass change, acidic precipitation, formation of clouds and fogs, changes in visibility, climate change, and human health assessment. This work presents a gas chromatographic method that uses a thermal conductivity detector (GC-TCD) to measure the liquid water mass (LWM) of collected aerosols. The method is a modification of the previously developed EA-TCD method (Lee and Hsu, 1998). The aerosol LWMs of NaCl, Na2SO4, NH4NO3, (NH4)2SO4 and NH4Cl were measured at 25℃ under relative humidities (RHs) varying between 20% and 90%, in both deliquescence and efflorescence conditions. The precision of this method is within ±3%. In addition, the deviation and average error of GC-TCD method compared with other literature’s data are within ±6% and ± 5%, respectively. In this work, the performance of the ISORROPIA, AIM2 and GFEMN thermodynamic models are compared with the measurements. The results indicate ISORROPIA model, a thermal equilibrium model for predicting the hygroscopic characteristics of most pure-salt inorganic aerosols, is the best and is adopted for investigating the hygroscopic characteristics of mixed aerosols. The mutual deliquescence relative humidity (MDRH) of various mixed fractions of NaCl-Na2SO4 and NH4NO3-NH4Cl binary-salt aerosol systems is found at 74% and 54%, respectively. In contrast, the MDRH of NaCl-Na2SO4-NaNO3 and NaCl-(NH4)2SO4-NH4NO3 tri-salt aerosol systems is 70% and 50%, respectively. The complete deliquescence relative humidity in these mixed aerosol systems is demonstrated to be dependent on the original aerosol composition. The deliquescence relative humidity (DRH) of NH4NO3 aerosol is shifted to higher value by decreasing the ambient temperature, as is evidenced by the DRH obtained at 54, 62, and 68% from the measurement at 35, 25, and 15℃, respectively. For the first time, the DRH and crystallization relative humidity of Na2CO3 aerosol presented by this method is 78% and 39%, respectively. Moreover, this work originally demonstrates the eutonic composition of NaCl-Na2SO4 binary aerosol is close to the composition of a solution with 90% NaCl and 10% Na2SO4. To date experimental data from complicated tri-salt aerosol systems have been very scarce. The data from this work and the comparison with model estimates facilitate the understanding of this aerosol system. Finally, an application of GC-TCD method to the measurement of LWM of atmospheric aerosol shows the fraction of aerosol water in PM2.5 can be ranged from 19 to 41% for ambient humid condition varying between 62 to 77% RH. |
