环境空气颗粒物中异构烷烃类物质的碳同位素组成研究

Isotoparaffin is an important biomarker among the organic contaminants associated with ambient air particulates, which constituent was very complicate, and its sources apportionment is hardly performed by the concentration feature. The researches on carbon isotopic composition of isoparaffin performed primarily in the geoscience field have reveal the sources and sedimentary environment of organic compounds. There have been some researches to reveal the sources by carbon isotopic composition of organic compounds based on the results from previous researches, which have showed the diversity of carbon isotopic compositions of organic compounds in various emission sources and the smaller isotopic fractionation during transportation and transfermation processes. However, there is no application of isotopic composition of isoparaffin to environmental field because of its constituent complicacy, so our research intends to trace the sources in atmospheric environment by constituent and carbon isotopic composition features of isoparaffin. For Taiyuan city, the contents of our research are as follows: researching the composition characteristics of isoparaffin derived from ambient air particulates and the suspected emission sources; establishing the carbon isotopic composition profile of isoparaffin derived from ambient air particulates and the suspected emission sources; revealing the carbon isotopic fractionation feature of isoparaffin during the attenuation processes; tracing the primary sources of isoparaffin by their composition and carbon isotopic composition features. Such results are crucial significance in tracing the source of isoparaffin in ambient air, what's more, it breaks a new cross-disciplinary field in the application of isotopic composition of isoparaffin to environmental science.

环境空气颗粒物中异构烷烃类有机污染物是一类重要的分子标志物，成分极其复杂，较难利用浓度特征解析来源。异构烷烃类物质的碳同位素研究主要用于地学领域，揭示有机物的来源和沉积环境。资料表明不同排放源有机物碳同位素有差异，在迁移转化过程中碳同位素分馏较小，已有利用其同位素组成研究来源的报道，但异构烷烃成分复杂，还未见异构烷烃类物质的同位素组成在环境领域的应用，故本题拟通过异构烷烃类物质的组分和碳同位素特征揭示其在环境空气中的来源。以太原市为例，研究环境空气颗粒物和主要排放源中异构烷烃类物质的组分特征；建立环境空气颗粒物和主要排放源中异构烷烃类物质的碳同位素组成成分谱；揭示降解过程中异构烷烃类物质碳同位素分馏特征；利用异构烷烃类物质组分和碳同位素特征示踪其来源。研究结果对示踪环境空气中异构烷烃类物质的来源具有重要的意义，更重要的是为异构烷烃的同位素组成在环境科学中的应用开辟了一条跨科学领域的新思路。

环境空气中颗粒物上异构烷烃可以提供污染源方面极其关键的信息，因其对指示大气颗粒物的来源具有重要作用而得到广泛关注。本项目实施过程中，以太原市为例，选取了7个具有代表性采样点采集了PM10样品，并由气相色谱质谱联用分析了异构烷烃化合物含量，利用气相色谱-同位素比值质谱仪技术测定了异构烷烃化合物的碳同位素（δ13C）组成，研究了环境空气和排放源颗粒物中典型异构烷烃的组成和碳同位素组成，分析了环境空气中的典型异构烷烃的来源，主要结论如下：.①环境空气和排放源颗粒物中典型异构烷烃（藿烷类化合物）的主要成分均为17A(H),21B(H)-藿烷 (C30AB)和17A(H),21B(H)-30-降藿烷 (C29AB)。无论是机动车和燃煤尘中，C30AB的含量均是C29AB的两到三倍。藿烷浓度不仅表现出明显的季节性差异（冬季为45.54–108.29 ng/m3，夏季为2.59–28.26 ng/m3），并且呈现出显著的市中心较高的空间差异。C30AB和C29AB的分析表明，在夏季汽车尾气为主要的藿烷类化合物的主要来源，燃煤贡献在冬季较夏季升高。.②汽油车尾气尘和柴油车尾气尘中检测出的典型异构烷烃（藿烷和甾烷）的碳同位素δ13C平均值分别为-28.6‰和-28.3‰，煤烟尘中颗粒物检测到的异构烷烃的δ13C平均值为-26.5‰；结果显示不同化合物之间的同位素差异适合通过同位素方法研究不同来源的藿烷和甾烷排放情况。太原市采暖季和非采暖季环境空气中PM10上δ13C平均值分别为-28.0‰和-28.3‰，采暖季比非采暖季略富13C。使用同位素质量平衡方程计算可知，在采暖季机动车排放的异构烷烃贡献值达75.92%，其中汽油车和柴油车排放贡献为47.21%和28.71%，燃煤贡献平均值为24.08%；在非采暖季，机动车排放的异构烷烃贡献平均值为89.60%，其中汽油车和柴油车排放贡献为67.50%和22.10%，燃煤贡献平均值为10.40%。.③本项目研究表明，随着城镇化的加快，环境空气中的颗粒物的组成发生了变化，颗粒物主要来源变为煤烟尘和机动车尘并重。分析显示，通过降低散煤燃烧来控制燃煤排放是城市控制颗粒物污染的基础，控制机动车排放是减少空气颗粒物污染、持续改善环境空气质量的重点。