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標題: | 機車尾氣粒狀物PM2.5採樣與量測方法開發 A sampling and measurement system for motorcycle exhaust PM2.5 |
作者: | Ji-Ying Lai 賴吉盈 |
指導教授: | 陳志傑(Chih-Chieh Chen) |
關鍵字: | 移動污染源,PM2.5,粒狀污染物, Mobile sources,PM2.5,Particulate matter, |
出版年 : | 2015 |
學位: | 碩士 |
摘要: | 機車因具有高機動性、便捷、停車方便與經濟等特性,成為台灣地區最普遍之個人交通工具。然而目前台灣針對使用中機動車輛的檢驗項目以氣狀污染物為主,對於粒狀污染物則缺少質量濃度與粒徑分佈的相關分析資料。再加上許多的研究證據顯示,粒徑是影響環境及健康效應的重要參數。因此本研究的目的在於發展一套針對使用中機車引擎尾氣排放粒狀污染物的即時採樣與量測系統。
實驗系統包含採樣緩衝腔、除溼裝置、旋風分徑器與量測儀器等單元。首先利用125 c.c.四行程機車引擎搭配動力計系統產生穩定的尾氣排放條件,以建立尾氣中含水率、粒狀物粒徑濃度分布以及微粒之吸濕成長特性,作為分徑與除水裝置設計之依據。此外也評估採樣濾紙在不同溫溼度、溫度與調理時間所可能造成採樣偏差的可能原因。另外也測試VPR (Volatile Particle Remover)在350℃的溫度下造成微粒粒徑分布與沉積損失的影響程度,並分析其搭配不同型式CPC (Condensation Particle Counter)所可能產生的量測偏差。之後再以實車於惰轉狀態下,驗證與比較不同儀器組合的性能與限制。在除水裝置方面,有稀釋法、Nafion dryer以及冰浴法;分徑裝置則以旋風分徑器為主;而微粒濃度量測方面則有濾紙秤重、SMPS、FMPS、CPC、microAeth AE51黑碳計等方法。 量測結果顯示實驗室之四行程機車引擎動力計排氣中的粒狀污染物,在惰轉狀態(1750 rpm)之下CMD約為0.05μm、GSD為1.8、數目濃度則為104~105 #/cm3。而從微粒之吸濕成長特性曲線可知尾氣中的微粒即使在相對濕度約100%的環境之下,並沒有顯著的吸濕現象。因此,稀釋的目的主要是為系統降溫,並避免凝結水於採樣管路中形成。樣本氣體含水量在惰轉狀態下約為7%,並隨著轉速增加而增加。當轉速最高為4000rpm時,約為10%。因此,當稀釋器的稀釋倍率約10倍應可避免凝結水的產生,不過其缺點是會降低粒狀物的濃度。雖然平板型Nafion dryer可以克服微粒濃度被稀釋的問題,而且在3 L/min之下對於次微米微粒(30~750 nm)無微粒穿透損失且能達到除水效果,但高價格造成其在實務上的可行性降低。而冰浴法操作簡單又能達到除溼與降溫效果。在旋風分徑器實驗結果證實我們可以針對不同的流率需求設計出符合美國EPA PM2.5效能曲線的分徑器。根據實驗發現鐵氟龍濾紙適合應用在車輛排氣採樣,且採樣溫度越高,濾紙受到半揮發性物質的影響也就越少,所需要的調理時間也就越短。目前歐盟使用的VPR應用在車輛採樣時可能會受到CPC的偵測下限影響而造成誤差,由於加熱會使得大部分微粒粒徑低於23 nm,因此歐盟SPN方法將低估實際引擎排氣中粒狀汙染物的濃度,但是否會提升量測的穩定度則需要進一步檢視。另外在實車測試結果顯示,化油器引擎,其質量濃度與數目濃度分別為730.4 μg/m3、2x106 #/cm3;電子噴射引擎其質量濃度與數目濃度分別為139.6 μg/m3、1.2x105 #/cm3。由於機車排氣的微粒中含大部分的揮發性物質,造成濾紙上所收集之微粒重量會隨著調理時間的增加而減少。因此,本研究所用之濾紙樣本重量統一以調理後第24小時值為代表。進一步FMPS、SMPS、AE51、CPC與機車尾氣濾紙質量濃度分別比對結果發現,以AE51黑碳計所獲得之相關性最好(r = 0.950),其次分別為FMPS(r =0.828)、SMPS(r=0.761)、CPC(r=0.798),再加上AE51具有使用方便、價格便宜以及相關性高等優點,並且其讀值不會顯著地受到揮發性物質的干擾,因此使用AE51黑碳計進行機車尾氣粒狀物檢測之攔檢作業是目前最可行的作法。 Motorcycle was an important transportation tool in tropical and subtropical countries. It becomes even more popular nowadays because of convenience, mobility and economy. In 2014, Taiwan had more than 14 million motorcycles, accounting for 64.7% of all motor vehicles. Many studies have been conducted to measure the quantity of regulated air pollutants such as CO, HC and NOx from motorcycles .In addition to these regulated air pollutants, the unregulated constituents can be significant because of particulate matter formation in urban areas and their potential health effects on human. Hence, the main objective of the present study was to develop a sampling and measurement system for PM2.5 emission from motorcycles. The sampling and measurement system was designed to include a chamber adapter connecting to tailpipe, a dehumidifying unit, an aerosol size-selective device, and an appropriate measurement instrument. The test particles were generated by using a 125 cc four-stroke engine controlled by a dynamometer. The particle size distribution, hygroscopic properties, and water content of emissions were evaluated before choosing the particle separator and dehumidifier. The effects of temperature, humidity, condition time on the filter weighting were evaluated. The particle penetration of VPR in different temperature were measured by SMPS. Several real-time aerosol instruments (SMPS, FMPS, CPC, AE51) were employed to measure the aerosol number concentration and/or size distribution, mass concentration, or black carbon. These measurements were then compared with the mass of filter samplers. The results indicated that the engine emission at idle mode (1750 rpm) had a CMD of 0.05 μm, GSD of 1.8, and number concentration of 104~105 #/cm3. The particles generated from motorcycle engine did not growth even if the RH was up to 100 %. Hence, the purpose of dilution was to decrease the sample temperature and avoid the water condensed on the sampling line. The sample water content was ranging from 7 % to 10 %, depending on the speed. Therefore, the dilution ratio of 10 was sufficient to avoid water condensation, but the drawback was the resultant low particle concentration. The Nafion dryer had almost no particle loss for particles from 30 to 750 nm, and had excellent dehumidifying efficiency, but it was expensive. The ice bath was cheap and simple to operate. It efficiently decreased the temperature and humidity of the motorcycle exhaust. The cyclones showed the same separation efficiency curve with the US EPA PM2.5 sampling convention. The results indicated that the PTFE filter was the most appropriate media for sampling particulate matter. The mass decrease due to semi-volatile matter decreased with increasing temperature of the sampling filter holder. The VPR reduced the particle size and resulted in the underestimation of particle number concentration, probably due to some of the particles smaller than 2.5 nm, the lower detection limit of ultrafine condensation particle counter. The aerosol emission measurements from motorcycles indicated that the particle mode was around 50 nm. The mass and number concentrations of carburetor engines were 730.4 μg/m3 and 2×106 #/cm3, respectively. For electronic injection engines, the mass and number concentrations were 139.6 μg/m3 and 1.2×105 #/cm3, respectively. The regression analysis showed that the correlation coefficients of the filtered mass against FMPS, SMPS, CPC and AE51 measurements were 0.761, 0.828, 0.798 and 0.950, respectively. Therefore, the combination of an ice bath, a cyclone, and the black carbon aerosol monitor (AE51) appeared to be most ideal for motorcycle exhaust PM2.5 measurements. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/17881 |
全文授權: | 未授權 |
顯示於系所單位: | 職業醫學與工業衛生研究所 |
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