Air Quality Research Center, University of California Davis, Davis, California, USA.
J Air Waste Manag Assoc. 2022 Nov;72(11):1316-1325. doi: 10.1080/10962247.2022.2119306. Epub 2022 Sep 23.
Thermal-optical analysis (TOA) has long been used to quantify organic carbon (OC) and elemental carbon (EC) on quartz-fiber filter samples collected in national ambient air monitoring networks. In the routine analysis of samples from the Chemical Speciation Network (CSN), we observed a considerable fraction of filter punches that remain gray or black in color after TOA was completed, suggesting the presence of EC that was not fully evolved at the highest temperature specified by the IMPROVE_A protocol (840°C). In this work, we explored the operational conditions necessary to evolve and quantify such residual EC. First, four heavily loaded CSN samples were analyzed to evaluate modifications to the IMPROVE_A protocol. We found that adding a higher temperature step at 930°C more effectively evolved the residual EC than did lengthening the duration of the 840°C step. Compared with the standard IMPROVE_A results, the modified protocol evolved additional EC of 1.08 to 4.45 µg cm in mass, or 0.12 to 0.50 µg m in concentration. This excess EC accounts for 27.1% to 45.3% of the total EC and 7.6% to 25.1% of the total carbon by standard IMPROVE_A. We then analyzed over 2600 samples from CSN using the extended IMPROVE_A protocol with higher maximum temperature (930°C). A total of 168 samples (6.4% of the total samples analyzed) contained measurable EC at the 930°C step. The average fraction of the evolvable residual EC mass in total EC is 5.7%, and up to 28% for samples with high total EC mass loading (i.e., 95th percentile and above). Our results suggest that CSN EC measured by the standard IMPROVE_A protocol should be considered a lower limit, and that a higher maximum heating temperature can be used to better quantify EC from CSN sites impacted by fresh urban emissions.
热光学分析（TOA）长期以来一直被用于量化国家环境空气监测网络中石英纤维滤膜样品上的有机碳（OC）和元素碳（EC）。在化学物质形态网络（CSN）的样品常规分析中，我们观察到相当一部分滤膜在 TOA 完成后仍然呈现灰色或黑色，这表明存在未在 IMPROVE_A 协议（840°C）规定的最高温度下完全演化的 EC。在这项工作中，我们探索了实现这种残留 EC 演化和量化的操作条件。首先，分析了四个负载较重的 CSN 样品，以评估对 IMPROVE_A 协议的修改。我们发现，在 930°C 增加一个更高的温度步比延长 840°C 温度步更有效地演化残留 EC。与标准 IMPROVE_A 结果相比，修改后的协议在质量上演化了额外的 1.08 至 4.45 µg cm 的 EC，或在浓度上演化了额外的 0.12 至 0.50 µg m 的 EC。这种过量 EC 占总 EC 的 27.1%至 45.3%，占总碳的 7.6%至 25.1%，按标准 IMPROVE_A 计算。然后，我们使用扩展的 IMPROVE_A 协议（最高温度 930°C）分析了来自 CSN 的 2600 多个以上的样品。共有 168 个样品（分析的总样品的 6.4%）在 930°C 温度步下含有可测量的 EC。可演化残留 EC 质量在总 EC 中的平均分数为 5.7%，对于总 EC 质量负荷较高（即第 95 百分位及以上）的样品高达 28%。我们的结果表明，标准 IMPROVE_A 协议测量的 CSN EC 应被视为下限，并且可以使用更高的最高加热温度来更好地量化受新鲜城市排放影响的 CSN 站点的 EC。
