Abstract. Thermal-optical measurement techniques are widely used for the monitoring of carbonaceous aerosols. Although results of different thermal-optical measurement techniques are comparable for total carbon, they can vary widely for values of elemental carbon especially in the presence of brown carbon. Charring of organic material during the inert heating phase of thermal-optical measurements was found to be a major confounder, but no literature about investigations of structural changes during this process in atmospheric aerosols is available. In a recent study we investigated these structural changes for combustion aerosol standard soot (CAST). Now we apply this approach to selected atmospheric aerosol filter samples and a subset of eight washed filter samples with low WSOCs loadings. To investigate structural changes, Raman spectra were obtained for samples heated to the corresponding temperature levels and gas atmospheres of the EUSAAR2 and NIOSH870 protocols. The temperature levels where changes in the Raman spectra occurred (i.e. changes in structure) varied for different samples. For the washed samples with low WSOC loadings and absence of other water soluble aerosol components such as inorganic salts, changes in structural ordering and darkening of the samples were not observed. For all samples, ion chromatography, integrating sphere measurements (yielding black and brown carbon data) and thermal-optical analyses were performed. We were able to show for the first time that the darkening of a sample (measured in terms of transmission laser signal) is not necessarily caused by an increase of structural ordering in the sample. Therefore we suggest that the widely used term charring should be used carefully when the darkening of a sample during thermal-optical measurement procedures is interpreted.

中文翻译：

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在两种热光学测量程序（EUSAAR2，NIOSH870）中研究大气气溶胶样品的结构变化

摘要。热光学测量技术被广泛用于碳质气溶胶的监测。尽管不同的热光学测量技术的结果对于总碳而言是可比的，但是对于元素碳的值，它们的变化可能很大，尤其是在存在棕色碳的情况下。人们发现，在热光学测量的惰性加热阶段，有机材料的炭化是一个主要的混杂因素，但是目前尚无有关在此过程中研究大气气溶胶中结构变化的文献。在最近的研究中，我们研究了燃烧气溶胶标准烟灰（CAST）的这些结构变化。现在，我们将这种方法应用于选定的大气气溶胶过滤器样本以及八个具有低WSOC负载的冲洗过的过滤器样本的子集。为了调查结构变化，对于加热到EUSAAR2和NIOSH870协议的相应温度水平和气体气氛的样品，获得了拉曼光谱。拉曼光谱发生变化（即结构变化）的温度水平因样品而异。对于洗涤后的WSOC含量低且不存在其他水溶性气溶胶成分（例如无机盐）的样品，未观察到结构有序变化和样品变黑。对于所有样品，均进行了离子色谱，积分球测量（获得黑色和棕色碳数据）和热光分析。我们能够首次证明，样品的变暗（根据透射激光信号测量）不一定是由于样品中结构顺序的增加所致。解释热光测量过程中样品变黑时，应小心使用炭化。