近道路測站超細懸浮微粒和非尾氣排放中金屬對人體之健康風險評估

Abstract

許多流行病學研究指出，大氣中的粒狀污染物 (Particular Matter, PM) 跟人體的健康息息相關。其中，氣動粒徑小於100 奈米的PM0.1，又稱超細懸浮微粒(Ultrafine Particles, UFPs) 的排放在城市地區不斷增加。由於其較小的粒徑，UFPs能夠隨著氣流穿越人體之上呼吸道並到達下呼吸道的肺泡區域且沉積在此處。近年來UFPs 引起了很大的關注，長期或短期暴露於UFPs 可能導致呼吸道症狀、肺部炎症、心血管疾病、腦部疾病以及神經退化性疾病。 都市地區的UFPs 最大的來源之一為交通排放，當污染物由車輛排氣管排放時，這些污染物被稱為尾氣排放；而當通過其他來源排放，例如燃料蒸發、道路灰塵再懸浮、煞車和輪胎磨損時，則稱為非尾氣排放。由於載具電動化導致電動車比例增加，導致非尾氣排放更為嚴重。目前對於非尾氣排放的規範不夠完善，非尾氣排放預計將成為近道路大氣中PM 污染的最重要來源，而非尾氣污染中含有許多重金屬，長期暴露於這些微粒可能會導致負面健康效應。 有效密度是微粒很重要的物理特性之一，因為它會影響微粒在大氣和人體呼吸道中的運動以及沉降行為，它還可以將微粒的電移動度粒徑轉換為氣動粒徑，而後者可以用來預測大氣中微粒運動行為。有效密度與微粒成分密切相關，亦是用於計算微粒肺部沉積比例時的重要參數之一。 為了識別都市地區微粒來源貢獻並估算其對人體健康之影響，本研究於台灣大學環境工程學研究所旁之移動測站 (IMPACT) 進行長期觀測。藉由掃描式電移動度粒徑分析儀 (Scanning Mobility Particle Sizer, SMPS) 及氣動粒徑分析儀(Aerodynamic Particle Sizer, APS) 量測12.5 到1,000 奈米之間的微粒數目濃度粒徑濃度 (Particle Number Concentrations, PNCs)，並利用正矩陣因子法 (Positive Matrix Factorization, PMF) 對測站附近的UFPs 和金屬污染物進行源解析，以識別近道路交通之貢獻。再利用氣膠微粒質量分析儀 (Aerosol Particle Mass analyzer, APM) 獲得之真實有效密度並結合多途徑微粒沉積模型 (Multiple-Path Particle Dosimetry Model, MPPD) 計算得到UFPs 在人體內的沉積比例。最後，利用奈米級多階衝擊板採樣器 (Nano-Micro-Orifice Uniform-Deposit Impactor, Nano MOUDI) 收集UFPs樣本後，再利用感應耦合電漿質譜儀 (ICP-MS) 分析金屬成分，來準確估計測站周圍金屬的呼吸沉積劑量以及暴露於超細懸浮微粒中的金屬之健康風險。 結果顯示，台北地區大氣環境中的金屬對人體的危害皆在可接受的範圍內，然而，對人體非致癌風險最高的金屬分別為鎳、錳及六價鉻，而致癌風險最高的金屬分別為六價鉻、砷以及鎳。除了已知的大氣有害元素鎳以及砷之外，與非尾氣排放有關的金屬，例如六價鉻以及錳，對人體的危害並不亞於鎳和砷，尤其是六價鉻，其對人體的致癌風險居冠。未來，隨著汽機車電動化程度的越來越高，控制煞車和輪胎磨損微粒將變得更加重要。這項研究使人們對都市地區的金屬污染物之來源提供更全面的了解，並強調了非尾氣排放對空氣品質的重要性。

Many epidemiological studies have indicated a significant correlation between particulate matter (PM) in the atmosphere and human health. Ultrafine particles (UFPs), with an aerodynamic diameter smaller than 100 nanometers, have been continuously increasing in urban areas. UFPs, due to their smaller size and the diffusion deposition mechanism, can penetrate deep into the human respiratory tract and deposit within the lungs. In recent years, UFPs have gathered greater attention, as inhalation exposure to them may result in respiratory symptoms, pulmonary inflammation, cardiovascular diseases, brain diseases, and neurodegenerative diseases. In urban environments, traffic emissions are a primary source of UFPs. These emissions are categorized into exhaust emissions from vehicle exhaust pipes and nonexhaust emissions from fuel evaporation, road dust resuspension, and brake and tire wear. Non-exhaust emissions, which can contain heavy metals, pose health risks and are expected to increase with the rise of electric vehicles. Currently, understanding about nonexhaust emissions is not comprehensive enough. Particle effective density is an important physical property for aerosols because it influences the settling behavior of particles in the atmosphere and human respiratory tract. It is an essential parameter for converting particle electrical mobility diameter to aerodynamic diameter and predicting particle aerodynamic behaviors, such as particle deposition in the lung. To identify urban particle sources and estimate their impact on human health, a longterm observation was conducted at the IMPACT (Integrated Mobile Platform for Atmosphere Composition and Temperature) station near the Graduate Institute of Environmental Engineering at National Taiwan University. Particle number concentrations (PNCs) between 12.5 and 1,000 nanometers were measured using a Scanning Mobility Particle Sizer (SMPS) and an Aerodynamic Particle Sizer (APS). Positive matrix factorization (PMF) was used to apportion UFPs and metal pollutants near the station to identify contributions from nearby traffic. The real effective density obtained from an Aerosol Particle Mass analyzer (APM) was applied to the Multiple-Path Particle Dosimetry Model (MPPD) to determine the lung deposition fractions of UFPs. Finally, after collecting UFP samples using Nano-Micro-Orifice Uniform-Deposit Impactor (Nano MOUDI), the metal composition was analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to accurately estimate the respiratory deposition dose of metals around the station and assess the health risks associated with exposure to ultrafine particulate matter. The results indicate that the harmful metals in the atmosphere of Taipei was within acceptable limits. However, the metals with the highest non-carcinogenic risk to humans were Ni, Mn, and Cr (VI), while the metals with the highest carcinogenic risk were Cr (VI), As, and Ni. In addition to the well-known harmful atmospheric elements Ni and As, metals associated with non-exhaust emissions, such as Cr (VI) and Mn, pose risks to human health comparable to Ni and As. Particularly, Cr (VI) has the highest carcinogenic risk to humans. In the future, as the electrification of vehicles increases, controlling particulate matter from brake and tire wear will become increasingly important. This study provides a more comprehensive understanding of the sources of metal pollutants in urban areas and emphasizes the importance of non-exhaust emissions to air quality.