- 學位論文
揮發性有機物之光化反應消耗對於台北萬華地區臭氧與二次有機氣膠生成潛勢之來源解析的影響
The effects of photochemical loss of volatile organic compounds (VOCs) on source apportionment of ozone and secondary organic aerosol formation potential in Wanhua, Taipei.
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摘要
鑒於近年來臭氧(O3)與二次有機氣膠 (Secondary Organic Aerosol, SOA)對於人體健康、氣候的嚴重影響，降低此二次污染物的危害已成為近年的重要議題。揮發性有機化合物(Volatile organic compounds, VOCs)為O3與SOA之重要前驅物，因此有必要對其排放來源管控。然而，由於VOCs在空氣中會被氧化劑快速消耗，導致其排放源之濃度與監測濃度有較大差異。為了瞭解VOCs排放源對於O3與SOA之影響，本研究對環保署的臺北市萬華光化測站之VOCs物種的小時值資料進行分析，其分析的資料時間段為2020年三月至2021年二月。在本研究中，VOCs在排放源之濃度(initial mixing ratio of VOCs, VOCsini) 計算為監測濃度 (observed mixing ratio of VOCs, VOCsobs)與反應消耗濃度(consumed VOCs, VOCscons)之總和，其考量了OH自由基與揮發性有機物在空氣中的反應消耗量。為了分析不同排放源對於O3與SOA生成之影響，臭氧生成潛勢 (Ozone Formation Potential, OFP) 與二次有機氣膠生成潛勢 (Secondary Organic Aerosol Formation Potential, SOAFP)皆以VOCsini進行計算。 本研究發現由VOCsini計算之臭氧生成潛勢(OFPini) 與監測之O3濃度(observed mixing ratios of O3)有具有高度相關性 (R2 = 0.82)，顯示OFPini為判定VOCs對O3生成貢獻之重要指標。在監測的VOCs中，烯類與芳香族為OFPini之重要貢獻者，而isoprene, toluene與m,p-xylene為其中最重要的OFPini貢獻物種。在SOAFPini中，芳香族佔據了大部分比例，而toluene與ethylbenzene為主要SOAFPini貢獻物種。台北萬華地區之VOCs排放來源經由正矩陣因子受體模式進行分析，鑑定出的排放來源包括生物排放源、石化工業源、家庭排放源、柴油排放源、工業溶劑源與汽油排放源，其中生物排放源、工業溶劑源與家庭排放源為重要的OFPini貢獻源，而工業溶劑源與家庭排放源為重要的SOAFPini貢獻源。本研究探討了VOCs與OH自由基反應消耗的重要性，在分析VOCs排放來源對於O3與SOA之生成貢獻時，需考量光化反應消耗並以VOCsini進行計算。此外，本研究解析了台北萬華地區之O3與SOA主要貢獻物種與排放來源，有利於未來針對該兩二次污染物減量策略的制定。
並列摘要
In recent decades, the pollution of ozone (O3) and secondary organic aerosol (SOA) has raised worldwide concerns due to their detrimental impacts on human health, air quality, and climate. To mitigate these problems, volatile organic compounds (VOCs), which play crucial roles as precursors for the formation of O3 and SOA, require regulation on their emission sources. However, the rapid oxidation of VOC species due to the oxidants in the atmosphere makes it difficult for assessing their mixing ratios at their sources, and thus impacts of VOC emission sources on O3 and SOA formation. To address this issue, a study was conducted in an urban area of Taipei, Taiwan, and the hourly data of 54 VOC species detected by Photochemical Assessment Monitoring Station (PAMS) from March 2020 to February 2021 was analyzed. The estimation of initial mixing ratios of VOCs (VOCsini), which means the mixing ratios from emission sources, was calculated by adding the observed VOCs (VOCsobs) to consumed VOCs (VOCscons), considering the kinetic reactions between VOCs and OH radicals. In addition, Ozone Formation Potential (OFP) and Secondary Organic Aerosol Formation Potential (SOAFP) were also estimated based on VOCsini, to find the contribution of VOC species to O3 and SOA formation. In this study, it was found that the OFP calculated based on VOCsini (OFPini) had high correlations with observed O3 mixing ratios (R2=0.82), implying that OFPini is a significant indicator when investigating the contribution of VOCs to O3 formation. Alkenes and aromatics were found as the dominant contributors to OFPini over the year, and isoprene, toluene and m,p-xylene were the top three contributor species. Aromatics predominate the total SOAFPini , and toluene and m,p-xylene were the most important contributor species. The analysis of emission sources of VOC species is based on positive matrix factorization (PMF), and the sources were identified as biogenic emissions, petrochemical emissions, consumer/household, diesel vehicle exhaust, industrial solvents and gasoline vehicle exhaust. Among these sources, biogenic sources, consumer/household and industrial solvents were found to be the dominant contributors to OFPini, while consumer/household and industrial solvents comprised the largest proportions in SOAFPini. This study highlights the significance of taking photochemical reactions between VOCs and OH radicals into account when estimating the contribution of VOCs emission sources to O3 and SOA formation. In addition, this study provides a reference for targeted reduction on dominant OFP and SOAFP contributors, and it is beneficial for mitigation of O3 and SOA pollution.
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