| 摘要: | 台灣環境保護署為了即時掌握臭氧前驅物的排放來源與了解物種與臭氧生成的關係，而增設光化學評估監測站 (Photochemical Assessment Monitoring Stations, PAMS)，每小時針對特定的54種揮發性有機化合物 (Volatile Organic Compound, VOCs) 進行連續性監測，其對應標準方法為NIEA A505.12B。除了PAMS，台灣環境保護署也對有害空氣污染物 (Hazardous Air Pollutants, HAPs) 列表中的VOCs進行環境濃度排放的監控。這些受管制的VOCs在一般空氣中濃度通常介於sub-ppb (v/v) 甚至到ppt (v/v) 等級，因此需要開發低偵測下限的分析技術以利於後續的HAPS連續監測。
為了監測VOCs的排放濃度，最有效的方法為連續監測技術，因此本研究為台塑企業建立連續監測技術，可根據六輕工業區 (Sixth Naphtha Cracker special industrial area, FPC) 的需求，針對特定12種目標化合物進行連續性的監測。一套完善的線上GC/MS系統，包括自製的除水裝置 (Dewater, DW) 及自製的濃縮系統 (Thermal Desorption, TD) 並與商業型的GC/MS/FID儀器串聯成DW-TD-GC/MS/FID與PAMS系統完全不同。PAMS系統是使用Nafion Dryer進行除水並搭配Perkin Elmer的氣相層析儀，由於GC/MS系統對於除水的條件比PAMS系統較為嚴苛，除了擔心會遺失掉極性物種外，殘留的水氣會使MS離子源受損，水氣在MS中會導致在其他GC偵測器中更嚴重的問題。在這項研究中，DW經測試後具有70%的除水效率，DW-TD設備可以與任何主流的商業型GC/MS串聯並用於連續性的監測。一套完善的DW-TD-GC/MS/FID線上系統還兼具警報功能，包括樣品管線壓力、溫度、流量和洩漏壓力計，若是數值未到達設定值，則會啟動警報功能。該設備部屬於FPC，採用NIEA A715.16B及NIEA A505.12B的方法，利用線上監測的方式以每小時量測VOCs和PAMS物種。12種目標化合物通過單一DB-1管柱利用分流的方式分別流至MS及FID，前者用於對12種目標化合物及未知化合物的物種定性，後者則針對12種目標物種進行定性及定量。台塑企業對於品保品管的標準提出要求，如線性 (R2) 需大於0.990，每日回收率需在85%~115%範圍內，各物種偵測下線 (MDL) 需低於1ppb。經過一年多的連續運行，事實證明自製的DW-TD與GC/MS/FID串聯其具有高穩定性及堅固性，至今仍依照計畫持續監測中。
;In order to understand the instantaneous mixing ratios of ozone precursors and the relationship between precursors and ozone production, Taiwan EPA has established the numerous Photochemical Assessment Monitoring Stations (PAMS) on the island to obtain hourly mixing ratios of 54 speciated VOCs based on the NIEA A505.12B method. In addition to the PAMS program, Taiwan EPA also announced several toxic VOCs as part of the Hazardous Air Pollutants (HAPs) to be regulated with the upper limits of emissions and ambient concentrations. The ambient limits of these regulated toxic VOCs are usually at sub-ppb (v/v) or even ppt (v/v) level, which calls for the need to develop measurement techniques with sufficiently low detection limits to facilitate online measurement.
In order to detect concentration spikes of toxic VOCs, the most effective way is the online approach. Therefore, this study established an online monitoring technique for the Formosa Plastics Corporation, which can perform continuous monitoring of 12 targeted compounds in accordance with the needs of the Sixth Naphtha Cracker special industrial area (FPC). An online GC/MS system that involves a self-built water removal unit, called dewater (DW), and a thermal desorption unit (TD) to couple with a commercial GC/MS/FID instrument to form DW-TD-GC/MS/FID. Different from the PAMS system that uses PerkinElmer′s gas chromatography with a Nafion dryer to remove water vapor in the sample, the GC/MS based system has a much more stringent dehydration requirement than the PAMS system due to the concern of loss of polar compounds. Moisture will cause more severe problems in MS than other GC detectors due to insufficient
vacuum from evaporation of residual water.
In this study, the DW was tested to have 70% water removal efficiency. The DW-TD device can couple with any major brand of GC/MS for online monitoring. The complete DW-TD-GC/MS/FID online system is also equipped with alarm mechanism to include sensors for the pipeline pressure, temperature, flow rate, and leak detection. If the set points are not reached, the corresponding alarm functions will be activated. This instrument was deployed at FPC by adopting the methods of NIEA A715.16B and NIEA A505.12B in an online mode to measure both toxic VOCs and PAMS species with hourly data resolution. The 12 target compounds were analyzed by a single column DB-1 and split at the end to both FID and MS. The MS is for the purpose of chemical identification of the 12 target compounds and the unknowns, whereas the FID for quantification of the 12 target compounds. Quality control criteria were set to require the linearity (as denoted by R-square) greater than 0.990, the daily recoveries within 85%~115%, and the detection limits less than 1 ppb. After more than a year of continuous operation, it has been proven that the self-made DW-TD with GC/MS/FID has demonstrated high stability and robustness, and it is still performing online monitoring as designed till this day. |
