Han Yongming, Chen Antony, Cao Junji, Fung Kochy, Ho Fai, Yan Beizhan, Zhan Changlin, Liu Suixin, Wei Chong, An Zhisheng
Key Laboratory of Aerosol Science & Technology, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China ; Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, United States of America.
Key Laboratory of Aerosol Science & Technology, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China ; Desert Research Institute, Reno, Nevada, United States of America.
PLoS One. 2013 Dec 17;8(12):e83462. doi: 10.1371/journal.pone.0083462. eCollection 2013.
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.
由于地壳物质、盐分和有机物质的干扰，对地质样品中的元素碳（EC）含量进行定量分析具有挑战性。热/光分析结合酸预处理是一种可行的方法。然而，从未对这类样品的各种热/光分析方法的一致性进行过检验。在本研究中，对来自中国宝鸡的城市街道灰尘和土壤样品进行酸预处理，并采用四种热/光方法进行分析，以研究分析条件和光学校正如何影响EC测量。结果发现，与采用透过率校正（ECT）测量的EC值相比，采用反射率校正（ECR）测量的EC值总是更高，且对温度程序的敏感性更低。延长加热时间的高温方法（STN120）显示出最高的ECT/ECR比率（0.86），而根据样品加载量调整加热时间的低温方法（IMPROVE - 550）显示出最低的比率（0.53）。与气溶胶样品的结果相反，STN的ECT高于IMPROVE的ECT。更高的峰值惰性模式温度和延长的加热时间可以通过在微量氧气条件下促进热解有机碳（PyOC）相对于EC的去除，从而提高预处理地质样品的ECT/ECR比率。考虑到滤膜中的PyOC会增加ECR，同时降低实际EC水平下的ECT，同时进行ECR和ECT测量将限制EC负载范围，并提供方法性能信息。使用常见环境基质的标准参考物质进行的进一步测试支持了这些发现。可以使用IMPROVE方法进一步分离EC的炭和烟炱部分。街道灰尘中的炭/烟炱比率（平均为2.2）低于土壤中的比率（平均为5.2），这很可能反映了机动车排放。烟炱浓度与纯热方法CTO - 375测得的EC一致。
