分析台灣都市地區粒狀污染物之氧化潛勢與其物化特性之關係

Abstract

近年來越來越多研究指出，顆粒物 (Particulate matter, PM)中的活性氧化物質 (Reactive oxygen species, ROS)為造成人體細胞損傷的主要原因，過多存在於人體中的ROS會導致體內氧化物質累積，進而造成氧化壓力 (Oxidative stress)的釋放。氧化潛勢(Oxidative potential, OP)常作為量化PM潛在毒性，以及研究PM與人體健康之相關性，其被廣泛定義為PM氧化目標分子之能力，亦可被視為產生ROS的能力。許多研究指出，不同的PM特性如排放源、物理特性、化學成分和其他大氣反應皆有可能會影響OP數值，換句話說，PM與健康之間的相關性僅部分取決於質量濃度，然而現今評估空氣品質標準還是以PM質量濃度為基準。為提供第一個較全面性之台灣都市地區OP與PM特性之間的相關性，本研究將監測站設置於主要道路及快速道路旁，進行為期約一個月的連續採集及監測研究，並同時利用影像辨識系統估算道路車流量及車種變化。有別於過往，本文使用新一代氣膠採樣器(Liquid spot sampler, LSS)取代傳統濾紙採樣，並結合dithiothreitol (DTT) 方法，提供早上(10:00-15:00 LT)及傍晚(16:00-21:00 LT)兩者之OP數值。LSS利用其內部三段充滿水之不同溫度生長管，製造出能使水蒸氣達到完全飽和狀態的區域，進入此區域內的PM會藉由不斷凝結至表面的水氣，使粒徑由奈米(nm)成長至微米(μm)等級最後被收集至下方水體中，對比傳統濾紙採樣，LSS不僅能收集水溶性和非水溶性之PM，也不需經過樣品前處理，能大幅降低樣本被污染之可能性亦可提高採樣之時間解析度。 研究結果顯示，單位體積的平均OP數值(Extrinsic OP, OPv)在早晚分別為0.46±0.27 nmol/min/m3 及0.48±0.26 nmol/min/m3，而單位質量的平均OP數值(Intrinsic OP, OPm)在早晚分別為41.3±13.8 pmol/min/μg及36.1±11.5 pmol/min/μg。由主成份分析法(Principal component analysis, PCA) 和線性迴歸結果可以得知OP的主要來源為汽機車污染。而與其它研究相比，本研究之OP數值略高於其他都市地區，這有可能歸因於測站設置在市中心之道路邊，大量地汽機車污染物如金屬、有機物等造成OP數值之提升。除此之外，在總觀測期間OPv與PM質量濃度及eBC兩者呈現良好的相關性，然而OPm的數值並未隨著PM 質量濃度的成長而提升，從此結果可以得知，質量濃度的高低並未能完全體現PM的毒性多寡。此外，根據褐炭(Brown carbon, BrC)的結果顯示，在本研究中有機物質可能為提升OPm的主要貢獻者之一，而值得注意的是，不同的天氣條件如日照強度、風速、濕度等皆有可能會造成OP數值的改變。

In recent years, the toxicological mechanisms of PM-related health effects are thought to involve the generation of reactive oxygen species (ROS) derived from particulate matter (PM), since it could induce oxidative stress and cause cellular damages. Oxidative potential (OP), defined as a measure of the capacity of particles to oxidize target molecules, can be viewed as the ability to generate ROS. Thus, OP is generally used as an indicator to quantify the potential toxicity of PM and to study the correlation between PM and human health. Several studies have shown that different PM characteristics such as emission sources, physical properties, chemical compositions and other atmospheric reactions could influence the OP. In other words, the health effect of PM is only partially determined by the mass concentration. In this study, to provide the first comprehensive relationship between OP and urban PM’s characteristics in Taiwan, a monitoring station was established and located next to a main street and expressway, the traffic flux was estimated in terms of analyzing camera videos simultaneously. PM samples were continuously collected by the Liquid Spot Sampler (LSS, AD series 110A), which is using a three-stage water condensational growth tube to directly collect all PM (including water-soluble and insoluble) into the working liquid, in two different periods of the day from December 24, 2019 to January 20, 2020. Sample’s OP is then determined by the dithiothreitol (DTT) assay. Compare with conventional filter collection, LSS can reduce the sample contamination and loss during the delivering and extraction process and increase the resolution of the sampling time. In this study, we provide two OP measurements per day by using LSS. Our results show that the average of the extrinsic OP (OPv) and intrinsic OP (OPm) are 0.46±0.27 nmol/min/m3 and 41.3±13.8 pmol/min/μg, respectively at period 1, while the average of the OPv and OPm are 0.48±0.26 nmol/min/m3 and 36.1±11.5 pmol/min/μg, respectively at period 2. The major source of OP in our sampling location is vehicle emission, confirmed by Principal Component Analysis (PCA) and linear regression results. Compared with other studies, our OP results are slightly higher than other urban areas, it might attribute to the high vehicular emissions, which contributed larger organic matters and trace metals especially as Mn, Fe, Pb and Cu. During the entire sampling period our result demonstrates that OPv followed a similar trend to PM mass concentration and has a reasonable correlation with equivalent black carbon (eBC) concentration, however, the OPm increases with the decreasing PM mass concentration, which should be noted that the currently regulation by using mass concentration might miscalculate the potency of particles’ toxicity. Based on the result of brown carbon (BrC), suggesting that the organic matters seem to be an important contributor to our OPm. The other notable finding is the photochemical reaction has a strong capability to have impacts on OPm, besides the meteorological conditions such as humidity, temperature or wind speed might also influence the OPv and OPm.