Hydrogen isotope analysis of benzene and toluene emitted from vehicles
Hydrogen isotope analysis of benzene and toluene emitted from vehicles
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DOI：
10.1016/j.atmosenv.2013.02.029
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发表时间：
2013-06
影响因子：
5
通讯作者：
Namiko Kikuchi;H. Kawashima
中科院分区：
文献类型：
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作者：
Namiko Kikuchi;H. Kawashima
大气挥发性有机化合物 (VOC) 的同位素分析，特别是氢同位素比 (δ2H)，有可能成为明确识别 VOC 来源的有效工具。然而，迄今为止，此类分析还很少。在这里，我们使用热解吸和色谱、热转换和同位素比质谱 (TD-GC/TC/IRMS) 分析了 VOC 的 δ2H 值。在确定高精度和准确分析所需的分析条件后，我们对低浓度样品采用最小峰面积阈值 10 Vs，对其他样品采用 15 Vs。我们还证实，样品吸附过程中的突破只会产生最小的影响。我们发现采集的样本至少可以保存7天。对于含有 58 种 VOC (C6–C11) 的标准气体中的 28 种标准化合物，获得了 1.1‰–5.3‰ (n = 7) 的精度。接下来，我们收集了五辆汽车在冷模式和热模式下产生的废气，并测量了δ2H值。对于苯，我们发现热模式车辆排放的δ2H值比冷模式轻19.3-104.7‰，而汽化汽油的δ2H值与冷模式接近0.7-25.2‰。因此，通过分析氢同位素比，应该可以区分冷模式车辆排放与热模式车辆排放。特别是对于苯，两种模式之间 δ2H 值的差异很重要，因为车辆通常会大量排放苯。此外，我们还测量了汽化汽油和路边空气中的挥发性有机化合物，并将结果与车辆排放的结果进行了比较。路边样品的特征主要是热模式。事实证明，如果假设大气中没有同位素分馏，热模式对路边 VOC 具有显着影响。结果表明，我们的方法可以通过测量更多目标化合物和来源的 δ2H 值，提高我们对大气 VOC 的起源和归宿的理解。
The isotopic analysis of atmospheric volatile organic compounds (VOCs), and in particular their hydrogen isotope ratio (δ2H), has the potential to be an effective tool for clearly identifying sources of VOCs. However, to date there have been very few such analyzes. Here, we have analyzed the δ2H values of VOCs using thermal desorption and chromatography, thermal conversion, and isotope ratio mass spectrometry (TD-GC/TC/IRMS). After determining the analytical conditions needed for high precision and accurate analysis, we adopted minimum peak area thresholds of 10 Vs for the low concentration samples and 15 Vs for other samples. We also confirmed that breakthrough during adsorption of samples would have only minimal effect. We found that the collected samples could be stored for at least 7 days. Precisions of 1.1‰–5.3‰ (n = 7) were obtained for 28 standard compounds in a standard gas containing 58 VOCs (C6–C11). Next, we collected the exhaust gas produced in cold mode and hot mode from five vehicles, and measured the δ2H values. For benzene, we found that the δ2H value for the hot mode vehicle emissions was 19.3–104.7‰ lighter than that for the cold mode, while the δ2H value of the vaporized gasoline was 0.7–25.2‰ close to that in the cold mode. It should, therefore, be possible to distinguish cold mode vehicle emissions from those of the hot mode by analyzing the hydrogen isotope ratio. For benzene, particularly, the difference in δ2H values between 2 modes is important since emitted in large quantity from vehicles generally. Additionally, we measured VOCs in vaporized gasoline and roadside air, and compared the results with those for vehicle emissions. The roadside samples were characterized mainly by the hot mode. It has been shown that the hot mode has a significant impact on roadside VOCs, if no isotopic fractionation in the atmosphere is assumed. The results suggest that our approach could improve our understanding of the origin and fate of atmospheric VOCs, by allowing measurement of the δ2H values of further target compounds and sources.