Abstract Two months (Oct.–Nov. 2015) of online elemental carbon (EC) and organic carbon (OC) measurements were performed by two field OC/EC Sunset Laboratory analysers working in parallel with an 8-h time resolution at a subarctic remote station in Finland. During such a time resolution, thermal OC and EC concentrations were usually close to or below the recent limits of detection for the analyser. Thus, this work highlights the possible issues to consider during the online measurements of OC/EC analysers working at the threshold of their analytical possibilities. A detailed analysis of the data showed that even though the OC concentrations were always above the detection limit of the analyser, up to 70% of the given concentration was due to the dynamic blank (gaseous phase). The majority of the OC aerosol was present in the less volatile fractions that evolved during steps at 300–450 °C and 450–650 °C. The main bias at low EC concentrations originated from the automatically determined split point between OC and EC. The results from the RTCalc526 software often led to an early determination of the OC-EC split point, resulting in an overestimation of the EC concentrations. However, the comparison of the results was performed after processing the OC/EC raw data in the different RTCalc software versions 526 and 703. The results showed that the EC values from the newer version of the RTCalc703 software were more consistent with the equivalent black carbon (eBC) results from optical instruments (aethalometer and MAAP) measured in parallel in comparison with results from the older RTCalc526 software. Equivalent BC data from the laser attenuation measurement of the Sunset Lab. analyser also provided better agreement with the newer version of the RTCalc software (RTCalc703).

中文翻译：

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亚北极远程站气溶胶中极低元素和有机碳浓度的在线测量

摘要 两个月（2015 年 10 月至 2015 年 11 月）的在线元素碳 (EC) 和有机碳 (OC) 测量由两台现场 OC/EC 日落实验室分析仪在亚北极偏远地区以 8 小时时间分辨率并行工作。芬兰站。在这样的时间分辨率期间，热 OC 和 EC 浓度通常接近或低于分析仪的最新检测限。因此，这项工作突出了在 OC/EC 分析仪在其分析可能性的阈值下工作的在线测量期间可能需要考虑的问题。数据的详细分析表明，即使 OC 浓度始终高于分析仪的检测限，高达 70% 的给定浓度是由于动态空白（气相）。大多数 OC 气溶胶存在于在 300–450 °C 和 450–650 °C 的步骤中产生的挥发性较低的部分。低 EC 浓度下的主要偏差源于 OC 和 EC 之间自动确定的分裂点。RTCalc526 软件的结果通常导致 OC-EC 分裂点的早期确定，从而导致 EC 浓度的高估。然而，结果的比较是在不同 RTCalc 软件版本 526 和 703 中处理 OC/EC 原始数据后进行的。 结果表明，来自较新版本的 RTCalc703 软件的 EC 值与等效黑碳更一致(eBC) 与旧版 RTCalc526 软件的结果相比，并行测量的光学仪器（测厚仪和 MAAP）的结果。来自日落实验室激光衰减测量的等效 BC 数据。分析器还提供了与较新版本的 RTCalc 软件 (RTCalc703) 更好的一致性。