Abstract Primary organic aerosol (POA) in diesel exhaust is semi-volatile and partitions mass between the gas and particle phases. POA volatility is not well understood for alternative fuels, varying engine loads, and for engines that feature modern emissions controls. In this study, we performed filter-based measurements of diesel exhaust from a modern-day non-road diesel engine for two different fuels (conventional diesel and soy-based biodiesel), two different engine loads (idle and 50% load), and with and without an emissions control device. Filters were analyzed offline to determine the POA volatility in two different ways: positive artifact on quartz filters at varying dilution ratios and speciation of alkanes. The POA volatility determined from our data suggests that POA mass emissions from diesel exhaust may be reduced by a factor of five with dilution to atmospherically relevant concentrations. These results are generally consistent with previous literature on POA volatility from non-road diesel engines but not with that from on-road diesel vehicles. POA volatility may hence need to be treated separately for non- and on-road sources in atmospheric models. Surprisingly, the POA volatility did not appear to vary under different combinations of fuel, engine load, and emissions control experiments performed, suggesting that POA might be dominated by unburned lubricating oil and its oxidation products. The POA volatility estimated from the speciation of alkanes was found to agree well with that determined from the dilution experiments. A kinetic model was used to calculate the gas/particle partitioning of POA in the dilution system. The modeling suggests that residence times in the dilution tunnel need to be on the order of minutes to allow the POA in the diluted exhaust to achieve gas/particle equilibrium. The use of short residence times (less than tens of seconds), similar to those used in conventional dilution systems, may bias the measurement of POA mass emissions in such systems and is of particular concern for emissions from cleaner, more modern combustion sources. The precise magnitude and direction of the bias depends on the exhaust temperature before dilution, tailpipe seed concentrations, dilution ratio, and residence times in the dilution tunnel. We recommend that kinetic models such as those used in this work be used, instead of using equilibrium assumptions, to inform the design and operation of the dilution tunnels as well to interpret the POA volatility from measurements made with those dilution tunnels.

中文翻译：

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现代非道路柴油发动机的主要有机气溶胶挥发性的测量和建模

摘要 柴油机尾气中的初级有机气溶胶 (POA) 是半挥发性的，在气相和颗粒相之间分配质量。对于替代燃料、不同的发动机负载以及具有现代排放控制功能的发动机，POA 的波动性还不是很清楚。在这项研究中，我们对现代非道路柴油发动机的柴油废气进行了基于过滤器的测量，用于两种不同的燃料（传统柴油和大豆基生物柴油）、两种不同的发动机负载（怠速和 50% 负载）和带和不带排放控制装置。离线分析过滤器，以两种不同的方式确定 POA 的挥发性：在不同稀释比下石英过滤器上的正伪影和烷烃的形态。根据我们的数据确定的 POA 挥发性表明，柴油机尾气中的 POA 质量排放量可以通过稀释到大气相关浓度减少五倍。这些结果与之前关于非道路柴油发动机 POA 挥发性的文献基本一致，但与道路柴油车辆的 POA 挥发性不一致。因此，大气模型中的非道路源和道路源可能需要分别处理 POA 的波动性。令人惊讶的是，POA 挥发性在燃料、发动机负载和排放控制实验的不同组合下似乎没有变化，这表明 POA 可能由未燃烧的润滑油及其氧化产物主导。发现从烷烃的物种形成估计的 POA 挥发性与从稀释实验确定的非常吻合。动力学模型用于计算稀释系统中 POA 的气体/颗粒分配。建模表明，稀释隧道中的停留时间需要在几分钟的数量级，以允许稀释排气中的 POA 实现气体/颗粒平衡。使用较短的停留时间（少于几十秒），类似于传统稀释系统中使用的那些，可能会使此类系统中 POA 质量排放的测量产生偏差，并且特别关注来自更清洁、更现代的燃烧源的排放。偏差的精确大小和方向取决于稀释前的排气温度、尾管种子浓度、稀释比和在稀释隧道中的停留时间。我们建议使用本工作中使用的动力学模型，而不是使用平衡假设，