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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/5961


    Title: 空氣中有機污染物自動分析技術之開發研究;壹?碳沸石多重床與中孔徑矽沸石之氣體吸附特性研究 貳?有機污染物垂直探空光化研究 Atmosphere volatile organic pollutants automatic analyzed system development research
    Authors: 吳季融;Ji-Rung Wu
    Contributors: 化學研究所
    Keywords: 揮發性有機物;中孔洞分子篩;臭氧前驅物;VOCs;mesoporous molecular sieves;ozone precusor
    Date: 2003-07-07
    Issue Date: 2009-09-22 10:11:05 (UTC+8)
    Publisher: 國立中央大學圖書館
    Abstract: 摘 要 本論文主要探討不同種類與孔徑的分子篩吸附劑對於空氣中揮發性有機物的選擇性與吸附能力;吸附劑共包含了四種不同的商業化碳分子篩吸附劑與兩種自行合成的矽分子篩吸附劑,製備單一吸附劑吸附管或組合式吸附管,搭配本實驗室自行開發之前濃縮系統,針對揮發性有機物進行量測。利用一已知濃度且包含56個物種分別為C2-C12之混合氣體做為樣品來源,研究各吸附管之吸附能力與選擇性。由於無法找到一吸附劑對於C3-C12物種皆具有良好的捕捉能力,故組合數種吸附劑形成一多重床吸附管,多重床吸附管則對於C3-C12物種皆具有一致的捕捉效率。 此外本研究也測試了兩種自行合成之矽分子篩吸附劑與商業化吸附劑作為比較,所合成之矽分子篩吸附劑分別為MCM-41與MCM-48,其孔洞大小各自為2.5 nm與2.8 nm,而商業化吸附劑孔洞則小於1.5 nm。其結果正如同所預測的,大孔洞的分子篩對分子小於C8-C10範圍的VOCs捕捉能力較差。相對地大孔洞的矽分子篩吸附劑則對大分子的物種有較佳的捕捉能力,大致上對於C8以上的物種,具有優良的捕捉能力。由以上結果可推論分子篩的孔洞大小決定了其吸附能力與選擇性。 本論文的第二部份則是針對台灣中部地區VOCs垂直濃度分佈之結果作討論;過去中部地區常發生季節性高臭氧問題,而高臭氧的來源可能是來自於上風處都會區所排放的VOCs與NOx經過傳輸後在下風處產生高臭氧的問題。量測過程中每一個垂直剖面是由7個繫掛於滯空氣球的Tedlar採樣袋所組成,採樣高度最高可達到距離地面1公里的高空。我們利用長生命期物種與短生命期物種之比值,作為氣團老化的證據。由數個垂直探空的結果中可以發現,VOC的濃度呈現極度不均勻的結果。一般而言靠近地表的VOC呈現較高的濃度且為較新鮮的氣團。而高層的氣團,則呈現VOC經過光化學反應後氣團老化的結果,其老化的現象對應了高臭氧的結果,驗證了高臭氧的來源是來自於上風都會區排放,經過遠距傳輸在下風處產生高臭氧的結果。 Abstract This study investigated the sorption selectivity of volatile organic compounds by various types of molecular sieve materials of different pores sizes, which consisted of 4 types of commercially available carbon based sorbents as well as two types of self synthesized silicon based mesoporous materials. These sorbents were packed either individually or in combination into a 9cm 1/8” O.D. s.s. tube to form enrichment traps used in a VOC analytical system. A standard gas mixture containing 56 C2-C12 species with known mixing ratios was analyzed by the traps for testing the enrichment efficiency and selectivity for these sorbents. While no single carbon sorbent can performed wide enough range of VOC sorption from C3-C12, the combination of several sorbents to form two multi-beds with one packed with carbosieve SIII, carboxen 1000 for the PLOT column, and the other packed with carbonxen 1000, 1003, and carbotrap, in this order, for the DB-1 column, however provided a uniform sorption efficiency across C3-C12. We also tested the sorption characteristics of two types of self-synthesized silicon based molecular sieves, which fall into the categories of MCM-41 and MCM-48 with pore sizes of 2.5 nm and 2.8 nm, respectively, significantly larger than those of carbon sorbents with pore size smaller than 1.5 nm in general. As expected, when using silicon molecular sieves poor sorption efficiencies were observed for VOCs smaller than C8-C10 region. Conversely, for molecules larger than C8-C10 region excellent trapping efficiency can be obtained, suggesting sorption selectivity and efficiency is largely controlled by the pore size. The second part of the thesis discusses the results from a field campaign in an attempt to obtain vertical distributions of VOC concentrations in central Taiwan where seasonal high ozone regularly plagues this area. It was postulated that the transport of VOCs and NOx from urban areas to the downwind rural areas causes maximum ozone formation. As a result, vertical profiles of VOCs mixing ratios were performed in a mountainous downwind area in an attempt to shed light to the transport theory. Each vertical profile was obtained from 7 air samples in Tedlar bags fastened along the string of a balloon elevated up to 1km. We used ratios of VOC pairs of longer lifetime species to short lifetime species to suggest the age of air masses. Based on several vertical measurements it was found that the VOC mixing ratios were highly inhomogeneous vertically and exhibited dramatic layer structure. While the layer near the surface usually showed higher VOC mixing ratios in general, the age of air masses in this elevation was significantly younger than those in the upper layer where aged air mass correlating with elevated O3 suggested long-range transport from upwind VOC source areas.
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