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Thermal/Optical Methods for Elemental Carbon Quantification in Soils and Urban Dusts: Equivalence of Different Analysis Protocols

机译：土壤和城市尘埃中元素碳定量的热/光学方法：不同分析规程的等效性

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摘要

Quantifying elemental carbon (EC) content in geological samples is challenging due to interferences of crustal, salt, and organic material. Thermal/optical analysis, combined with acid pretreatment, represents a feasible approach. However, the consistency of various thermal/optical analysis protocols for this type of samples has never been examined. In this study, urban street dust and soil samples from Baoji, China were pretreated with acids and analyzed with four thermal/optical protocols to investigate how analytical conditions and optical correction affect EC measurement. The EC values measured with reflectance correction (ECR) were found always higher and less sensitive to temperature program than the EC values measured with transmittance correction (ECT). A high-temperature method with extended heating times (STN120) showed the highest ECT/ECR ratio (0.86) while a low-temperature protocol (IMPROVE-550), with heating time adjusted for sample loading, showed the lowest (0.53). STN ECT was higher than IMPROVE ECT, in contrast to results from aerosol samples. A higher peak inert-mode temperature and extended heating times can elevate ECT/ECR ratios for pretreated geological samples by promoting pyrolyzed organic carbon (PyOC) removal over EC under trace levels of oxygen. Considering that PyOC within filter increases ECR while decreases ECT from the actual EC levels, simultaneous ECR and ECT measurements would constrain the range of EC loading and provide information on method performance. Further testing with standard reference materials of common environmental matrices supports the findings. Char and soot fractions of EC can be further separated using the IMPROVE protocol. The char/soot ratio was lower in street dusts (2.2 on average) than in soils (5.2 on average), most likely reflecting motor vehicle emissions. The soot concentrations agreed with EC from CTO-375, a pure thermal method.
机译：由于地壳，盐和有机物质的干扰，对地质样品中的元素碳（EC）含量进行量化具有挑战性。热/光学分析结合酸预处理代表了一种可行的方法。然而，从未检查过用于这种类型样品的各种热/光学分析方案的一致性。在这项研究中，对来自中国宝鸡的城市街道灰尘和土壤样品进行了酸预处理，并通过四种热/光学方案进行了分析，以研究分析条件和光学校正如何影响EC测量。发现用反射率校正（ECR）测量的EC值总是比用透射率校正（ECT）测量的EC值更高，对温度程序的敏感性更低。延长加热时间的高温方法（STN120）显示最高的ECT / ECR比（0.86），而低温协议（IMPROVE-550）的加热时间根据样品上样进行调整，则显示最低（0.53）。与气溶胶样品的结果相反，STN ECT高于IMPROVE ECT。较高的惰性模式峰值温度和延长的加热时间，可通过在痕量氧气下促进EC上的热解有机碳（PyOC）去除，从而提高预处理地质样品的ECT / ECR比。考虑到过滤器内的PyOC会增加ECR，而与实际EC水平相比会降低ECT，因此同时进行ECR和ECT测量会限制EC的负载范围，并提供有关方法性能的信息。使用常见环境基质的标准参考材料进行的进一步测试支持了这一发现。可以使用IMPROVE协议进一步分离EC的炭黑和烟灰部分。街道灰尘中的煤烟比（平均为2.2）低于土壤（平均为5.2），最有可能反映了机动车的排放。烟尘浓度与纯热法CTO-375的EC一致。

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