| Abstract: | 近地表臭氧成為近年來我國相當重視的議題。由於揮發性有機化合物(Volatile organic compounds, VOCs) 為產生臭氧的前驅物，若是要解決臭氧的問題，必須了解臭氧前驅物VOCs，而我國對VOCs的計量即以量測非甲烷總碳氫化合物 (Non-methane hydrocarbons, NMHC) 為主，且NMHC也為大氣中進行光化反應的主要物種，因此NMHC的監測非常重要，NMHC的計算方式為總碳氫化合物 (Total hydrocarbons, THC) 減去甲烷 (Methane)，其中甲烷雖然不是VOCs但也是重要的溫室氣體，因此甲烷的監測也有其必要性。
本研究主要依照環境檢驗所公告之標準方法NIEA A740.10C進行觸媒法總碳氫分析儀的開發，對於硬體及軟體進行改良使儀器的穩定度得到改善，並依照標準方法規範進行穩定性測試，測試結果零點偏移THC為0.06、CH4為0.07、NMHC為0.03ppm，全幅偏移THC為-0.32、CH4為-0.07、NMHC為-0.25ppm，反應時間為83秒，皆在規定範圍之內。測試完畢後也將開發之機台移至台北市環保局空氣品質監測測站中實際進行監測，監測期間發現到測站內採樣歧管加裝的過濾器中的濾紙因為吸附空氣中粒狀物使得阻抗變大會造成進入FID流量發生變化，由於在先前的儀器架構中並未針對流量進行控制，因此本研究嘗試使用質量流量控制器 (Mass flow controller, MFC) 控制進入FID的樣品流量以改善FID流量發生變化的問題，加裝MFC觸媒法機台後續也與實驗室根據NIEA A723.75B開發管柱層析逆吹法機台進行比測，兩者比測結果具有相同的趨勢，觸媒法展現出更高的穩定性。
光化測站萬華站乙烷測值常年偏高，推測排放源為天然氣洩漏，本研究藉由光化測站乙烷數據以及空品站中甲烷數據進行分析，在乙烷高值事件時也可同時觀察到甲烷的高值且兩者具有高度相關性，進一步證明萬華站的乙烷是來自天然氣而不是交通源，之後再使用後推軌跡嘗試尋找天然氣來源，經過比對後推測天然氣來自於西門町內之餐廳。
;Near-surface ozone has become a critical issue for Taiwan in recent years. Since volatile organic compounds (VOCs) are the precursors of ozone generation, we must understand the ozone precursors’ VOCs. Furthermore, the amount of VOCs in Taiwan is represented by the measurement of non-methane hydrocarbons (NMHC), which is also the main species for photochemical reactions in atmosphere, thus it’s crucial to monitor NMHC. NMHC is calculated as Total hydrocarbons (THC) minus methane, of which methane is not a VOC but is also an important greenhouse gas, so methane monitoring is also necessary.
The study followed the standard method NIEA A740.10C announced by the National Institute of Environmental Analysis to develop a catalytic total hydrocarbon analyzer. The instrument′s stability was improved by both hardware and software, and the stability test was carried out according to the standard method specification. Zero and full-scale drift test results THC is 0.06 and -0.32, CH4 is 0.07 and -0.07, NMHC is 0.03 and -0.25ppm, and the response time is 83 seconds, all within the specified range. After the completion of laboratory test, the developed machine was moved to Taipei City’s Air Quality Station (AQS) for field monitoring. During the monitoring period, it was found that the filter paper used in the station had changed the flow rate entering the FID due to the adsorption of particulate matter in the air, which makes the resistance more significant. Since the flow rate was not controlled in the previous instrument architecture, this study attempted to use mass flow controller (MFC) to control the sample flow into the FID which improved the problems of FID flow change. Comparing machine which installed the MFC catalyst with laboratory-developed back-flush GC method according to NIEA A723.75B, results showed that both trends were identical. Moreover, the MFC catalyst method showed higher stability than back-flush GC method.
The ethane measurement value of the Wanhua station’s photochemical assessment monitoring station (PAMS) is high year-round which was speculated that the emission source is natural gas leakage. By analyzing the ethane data of the PAMS and the methane data of the AQS, the high value of methane could also be observed at the same time in the event of ethane’s high value which showed highly correlated. Thus, this study proved that the ethane value of Wanhua station was came from natural gas instead of transportation source. Additionally, this study found out the source of natural gas by using the backward trajectory. After comparison, it is speculated that the natural gas comes from the restaurants in Ximending. |
