环境空气中挥发性有机物的稳定氢同位素组成研究

VOCs compounds are known as the precursors for photochemical reactions. It is of significant and scientific meaning to identify the source and transformation of the precursors. Because they are liable to react in the ambient air, the concentration analysis for the source and transformation is subject to uncertainty. In recent years, stable carbon isotope technology has been applied to the research into the source and transformation of the pollutants. However, there is little difference of carbon isotope in some of VOCs compounds. Hence, it is quite difficult to utilize the carbon isotope difference alone to research the source and transformation of the partial VOCs. Carbon and hydrogen are the main elements of VOCs. During the process of physics, chemistry or biology, there is the maximum relative mass difference and a higher level of isotope fractionation between protium and deuterium. The information embodied in stable hydrogen isotope is of special environmental meaning, thus providing a special insight into the research into the source and transformation of the pollutants. At present, there are few literatures and reports devoted to the stable hydrogen isotope composition of the partial VOCs emission sources. The research into the stable hydrogen isotope of VOCs in the ambient air is still lacking. By taking Taiyuan City as an example, this paper aims to research the VOCs composition in the main emission source and ambient air. The alkane and benzene that comprise a small portion of isotope fractionation are utilized to explore the possible source. The isotope fractionation effect of the olefin is utilized to research the chemical conversion under the condition of photo degradation. Hence, it can provide new insight and methods for the research into the source and transformation of VOCs in the ambient air.

挥发性有机物（VOCs）是光化学反应前体物，查明其来源转化具有重要的科学意义。由于其在环境空气中易发生反应，用浓度分析其来源转化存在不确定性。近年来稳定碳同位素技术正应用于污染物来源转化研究，但部分VOCs排放的部分化合物碳同位素值差别较小，单一利用碳同位素差异较难研究部分VOCs的来源转化。碳和氢是其两种主要元素，在物理、化学或生物过程中，氕与氘之间具有最大相对质量差及更大同位素分馏，氢同位素组成所蕴含的信息具有特定环境意义，对污染物来源转化研究具有独到之处。目前仅鲜少文献报道部分VOCs排放源氢同位素组成，还未见有环境空气中VOCs氢同位素组成研究。本项目以太原市为例，研究主要排放源和环境空气中VOCs氢同位素组成；利用氢同位素分馏较小的烷烃、苯等氢同位素组成探讨其可能来源；利用烯烃类氢同位素分馏效应研究其光降解及臭氧作用下化学转化，为环境空气中VOCs来源转化研究开辟新思路、新方法。

挥发性有机物（VOCs）是PM2.5和O3的前体物，查明其来源和转化具有重要的科学意义。近年来稳定碳同位素技术广泛应用于污染物来源转化研究，但部分VOCs排放的部分化合物碳同位素值差别较小，单一利用碳同位素差异较难研究部分VOCs的来源转化。氢是一种重要元素，本项目研究了燃煤源、机动车尾气源、汽油挥发源和溶剂使用源样品中挥发性芳香烃VOCs的稳定氢、碳同位素组成，分析组成特征，探讨其转化过程。以太原市为例，研究太原市不同点位环境空气中VOCs的浓度组分及同位素组分并探讨其来源。对于各排放源中挥发性芳香烃VOCs的碳、氢同位素研究结果显示：（1）与汽油挥发源中挥发性VOCs相比，机动车尾气中δ13C值显著富集13C，苯的富集程度最大，利用此特性可判断环境空气中机动车尾气来源。（2）机动车尾气中苯的δD值与汽油中苯的δD值相比显著贫D，机动车尾气中的苯可能为汽油中大分子热解生成的小分子不饱和烃生成。（3）燃煤源中挥发性芳香烃VOCs与机动车尾气源、汽油挥发源、溶剂挥发源相比富集13C、贫D。（4）太原市各采样点中，小店点位挥发性芳香烃类VOCs的δ13C与上兰和桃园点位相比富集13C。（5）基于正交矩阵因子分解法（PMF）分析环境空气中VOCs来源，结果显示太原市VOCs只要来自于燃煤源、机动车源和挥发源；基于碳、氢同位素分析的Isosource模型和质量平衡方程线性拟合结果显示燃煤源、机动车源是主要的挥发性芳香烃类VOCs的排放源。因此，减少煤炭的使用，控制机动车排放，是减少太原市环境空气中的VOCs污染的重要途径。