本研究開發一種線上自動氣相層析方法，線上分析大氣中輕質(C2-C3)揮發性有機化合物，即乙烷、丙烷、乙烯與丙烯的空氣背景濃度。此系統設計的發想是源於2014年高雄因丙烯輸送管線破裂導致氣爆。希望可在大型石化園區或是在住家周圍能早期偵測到乙烯、丙烯原料氣體或是天然氣、液化石油氣之洩漏，建立預警防災能力。 為達到長期線上自動監測目的，此系統將恆溫逆吹的功能加入氣相層析方法中，可將高沸點物質吹離管柱，以達到管柱自我清潔而不需高溫烘烤之功能，使管柱可長期連續使用，亦可大幅降低分析時間且增加設備之穩定性，可在數分鐘內得到單筆數據。 除了作為預防氣爆之目的外，本研究亦將此系統應用於監測境外氣團移入。在2016年11月1日至12月8日期間，位於台灣最北端的富貴角測站進行上述五種氣體背景濃度觀測，進而得到彼此物種間的比值，用以指示境外污染氣團移入。甲烷、乙烷、丙烷與乙烯、丙烯五種氣體彼此的生命期都相差甚大，故可以利用彼此間的濃度比值而得知是否為境外傳輸之氣團，並可辨別與本地氣團之差異。在監測過程中觀測到明顯境外傳入的特徵出現，所測得的ethane/ethylene比值和O3、NOx出現一致性的特徵，證實此方法可作為長程傳入污染監測之用。 本研究亦對於實地監測時所遇到的水氣問題進行探討，開發一種物理冷凍除水系統，與市售之除水設備Nafion dryer 相比，不需大量乾燥氣體，且可以觀測極性物質不受親水膜的影響，大幅度減少空間與人力的維護。 ;This study is aimed to develop an on-line automated gas chromatographic (GC) method to analyze highly volatile organic compounds (VOCs) at ambient level. These VOCs are ethane, propane, ethylene and propylene, which are widely used as fuel, raw materials, or reagent in industrial applications. In light of the catastrophic accidient occurred in Kaohsiung in 2014 due to propylene leakage from the underground pipelines, the original intention was to use the GC system to serve as an early warning tool to detect the very early stage of leakage.
In this system, the back-flush design is used to remove the higher boiling VOCs from the columns by reversing the carrier gas flow in the analytical column to shorten the analysis time and, at the same time, refresh the columns. Each analysis can be completed within a few minutes. This system was also used to monitor the background air by taking the advantage of its good sensitivity and stability. Because the four measured compounds have large different in their atmospheric lifetimes, the ratios of long to short can be used to indicate the arrivals of long-range transport (LRT) events. For instance, the ratio of ethane/ethylene increased coherently with ozone during a LRT event encountered at Cape Fuguei on 6 December 2016. NOx dropped significantly during the event because of its short atmospheric lifetime. By contrast, low ethane/ethylene and distinct diurnal cycle of ozone were observed on the days dominated by local emissions. To meet the needs of long-term operation, a water removal method was developed to avoid the use of a Nafion dryer. An empty glass tube is placed upstream of the sampling sorbent trap to condense water vapor at the temperature of -20°C on the same cooling device. During injection, the water trap is heated up to 300°C to backflush with nitrogen to remove water from the trap.
