| 摘要: | 本實驗旨在開發一套新的分析系統，整合自建的除水 (DW) 和熱脫附 (TD) 單元與氣相層析儀 (GC)，並透過三項創新優化提升對 VOCs 的捕集效率、分析物種的廣度、靈敏度與準確性。首先，為有效降低樣品中分子活性並提升分析準確性，本系統改善前濃縮核心模組的降溫能力，將樣品捕集溫度降至 -30 °C，進一步提升對輕碳分子的捕集效率。其次，本研究優化實驗室常用的四重床配置，改為二重床設計，選擇保留對輕碳物種具有良好吸附能力的 Carbosieve SIII 和對重碳物種具較強吸附力的 Carbontrap。在分析方面，本系統採用 Deans switch 切換閥件，實現 Heart-cut 分離技術，針對 C2 至 C12 範圍內，共 55 種光化前驅物進行高效分離，通過使用兩種不同固定相的層析管柱，較輕的 VOCs (C2-C6) 將被導入 PLOT 層析管柱進行分離，而較重的 VOCs (C6-C12) 則通過 TG-1MS 層析管柱分離，最後透過兩顆火焰離子偵測器 (FID) 進行檢測。系統分析重複性 (RSD)介於 0.305% 至 1.924%，檢量線線性 (R²) 皆高於 0.995，偵測極限 (MDL) 介於 0.014 至 0.095 ppb，展現出本系統的高精密度與穩定性。第三，為達成 VOCs 與氯氟碳化物 (CFCs) 同步分析的目標，本系統採用分流技術 (split flow)，將樣品同時導入第二台氣相層析儀 (GC)，搭配電子捕捉偵測器 (ECD)，用於分析 CFC-11、 CFC-12、CFC-113 和 CCl₄。此系統亦展現優異表現，R² 值介於 0.995 至 0.999，RSD 範圍為 0.118% 至 0.578%，充分證明整體分析流程具良好穩定性與高準確性，為數據的可行性提供了有力證據。
本系統已成功應用於基隆地區的無人機垂直採樣作業，完整獲得 55 種 VOCs 以及 CFCs 等氣體的三維濃度分布資訊。樣品採樣高度涵蓋 0、100、300 及 500 公尺共 4 個高度，結果顯示輕碳物種（如乙烷、乙烯）與芳香烴類濃度變化明顯，揭示大氣中 VOCs 在垂直方向具有顯著的不均勻分布，反映其受多重排放源與大氣傳輸機制的交互影響。相對地，CFC-12 與 CFC-113 濃度穩定、變化幅度極小，接近背景值，顯示其可作為內部標準物質，不僅有助於驗證數據品質，亦可作為 VOCs 垂直變化的參照依據，進一步提升資料解析的可信度。
此次無人機研究亦結合地面測站資料，將垂直採樣結果與北部高排放區的土城光化測站觀測組成進行比對，作為判斷氣團老化程度的參考，有助於解析垂直濃度變化的可能來源，比對結果也驗證本系統數據與現有光化監測資料具有良好的可比性。
;This study aimed to develop a novel analytical system integrating self-constructed dehydration (DW) and thermal desorption (TD) units with a gas chromatograph (GC). Three innovative optimizations were implemented to enhance the system’s efficiency in capturing volatile organic compounds (VOCs) and to improve analytical scope, sensitivity, and accuracy.
First, to reduce molecular activity in the samples and enhance analytical precision, the system′s core pre-concentration module was modified to improve its cooling capability, lowering the trapping temperature to -30 °C. This adjustment significantly enhanced the capture efficiency of light hydrocarbons. Second, the conventional four-bed sorbent configuration commonly used in laboratories was simplified to a two-bed design, retaining Carbosieve SIII for its strong adsorption capacity for light VOCs and Carbontrap for its efficacy with heavier compounds.
For compound separation, the system employed a Deans switch valve to implement heart-cutting techniques, enabling efficient analysis of 55 photochemical precursors ranging from C2 to C12. Two chromatographic columns with different stationary phases were used: lighter VOCs (C2-C6) were routed to a PLOT column, while heavier VOCs (C6–C12) were separated using a TG-1MS column. Detection was carried out using two flame ionization detectors (FID). The system demonstrated excellent performance, with relative standard deviations (RSD) ranging from 0.305% to 1.924%, calibration curve linearity (R²) exceeding 0.995, and method detection limits (MDL) between 0.014 and 0.095 ppb, reflecting its high precision and stability. Third, to enable simultaneous analysis of VOCs and chlorofluorocarbons (CFCs), the system utilized a split flow technique to direct part of the sample stream into a second GC equipped with an electron capture detector (ECD). This setup was used to analyze CFC-11, CFC-12, CFC-113, and carbon tetrachloride (CCl₄) with R² values between 0.995 and 0.999 and RSD ranging from 0.118% to 0.578%. This system was successfully applied to UAV-based vertical sampling operations in the Keelung area, where three-dimensional concentration distributions of 55 VOCs and CFCs were obtained. Samples were collected at four altitudes—0, 100, 300, and 500 meters. The results showed significant concentration variations for light hydrocarbons (e.g., ethane, ethylene) and aromatic compounds, indicating pronounced vertical heterogeneity of VOCs in the atmosphere. This pattern reflects the combined effects of multiple emission sources and atmospheric transport mechanisms. In contrast, the concentrations of CFC-12 and CFC-113 were stable, showing minimal variation and remaining close to background levels, demonstrating their suitability as internal standards. These compounds not only help validate data quality but also serve as reference indicators for interpreting VOCs vertical variation, thereby improving the credibility of data interpretation.
Additionally, this UAV-based study was integrated with data from a ground-based monitoring station. The vertical sampling results were compared with observations from the Tucheng Photochemical Monitoring Station, located in a high-emission area in northern Taiwan, to assess air mass aging. This comparison provided insights into the possible origins of vertical concentration variations and further confirmed the consistency between data produced by this system and existing photochemical monitoring data. |
