Abundance and Group Reactivity of Intermediate Volatility Organic Compounds (IVOCs) in Urban Air Measured by TD-PTR-MS

这项建议的主要目标是开发一种方法来量化城市空气中中挥发性有机化合物(IVOCs)的丰度。这些化合物含有12到18个碳原子，在柴油发动机尾气中排放，被认为是活性有机化合物的重要来源，有助于形成二次有机气溶胶(SOA)。对IVOCs的丰度和大气化学知之甚少。这一建议将建立一种热解吸采样与质子转移反应质谱仪(TD-PTR-MS)联用来定量空气中IVOCs的新方法。用这种方法将测量IVOC烷烃的总丰度。该方法将通过将IVOC物种归类为官能团(即烷烃、环烷烃)或按其相对分子质量(即单环芳烃、萘)对IVOC碳库进行更全面的量化。该方法将用于为期四周的野外采样活动，将IVOC丰度与PTR-MS和GC-MS测量的挥发性有机化合物(VOC)丰度进行比较，以检验IVOC光氧化是城市SOA的主要来源这一命题。使用光反应反应室的实验室实验将用于对柴油和柴油机废气进行光化学老化，以建立IVOC基团与羟基自由基的反应。这些实验将有助于对现场数据的解释，并加强目前对化学输运模拟所需的IVOC寿命的稀疏了解。建立一种定量空气中IVOCs丰度的测量方法，解决了城市空气光化学和SOA形成方面的知识空白。这项研究将支持和培训两名研究生和一名本科生对有机痕量气体的分析和解释。使用的结果和仪器将被纳入本科生课程和高级空气质量实验室课程。研究成果将通过会议和同行评议的期刊传播。这一结果将加深我们对大气中有机化合物的性质和来源的了解。公众的利益将是对城市空气中柴油发动机废气的水平和影响有更多的量化了解。

The primary objective of this proposal is to develop a method to quantify the abundance of intermediate volatility organic compounds (IVOCs) in urban air. These compounds contain 12 to 18 carbon atoms, are emitted in diesel engine exhaust, and are thought to be a significant source of reactive organic compounds that contribute to the formation of secondary organic aerosol (SOA). The abundance and atmospheric chemistry of IVOCs is very poorly understood. This proposal will establish a novel method for quantifying IVOCs in air by using thermal desorption sampling coupled to proton transfer reaction mass spectrometry (TD-PTR-MS). With this approach the total abundance of IVOC alkanes will be measured. The approach will allow a more comprehensive quantification of the IVOC carbon pool by lumping IVOC species into functional groups (i.e., alkanes, cyclic alkanes) or by their molecular weight (i.e. monocyclic aromatics, naphthalenes). The method will be used in a four week field sampling campaign to compare IVOC abundance to volatile organic compound (VOC) abundance measured by PTR-MS and gas chromatography mass spectrometry (GC-MS) to test the proposition that IVOC photooxidation is a major source of urban SOA. Laboratory experiments using a photoreaction reaction chamber will be used to photochemically age diesel fuel and diesel engine exhaust to establish IVOC group reactivity with hydroxyl radical. These experiments will aid the interpretation of field data and enhance the currently sparse knowledge of IVOC lifetimes required for chemical transport modeling. Establishing a measurement method to quantity the abundance of IVOCs in air addresses a critical gap in knowledge of urban air photochemistry and SOA formation.The research will support and train two graduate students and one undergraduate student in analysis and interpretation of organic trace gas. Results and instrumentation used will be incorporated into undergraduate classes and a senior level air quality laboratory class. Research results will be disseminated through conferences and peer reviewed journals. The results will enhance our understanding of the nature and origin of organic compounds in the atmosphere. The public benefit will be a more quantitative understanding of the levels and impacts of diesel engine exhaust in urban air.