Abstract Light-absorbing organic particulate matter (PM), or brown carbon (BrC), may constitute an important fraction of combustion PM. Here, we investigate the effect of combustion conditions on the molecular sizes of BrC, their light-absorption properties, and their cytotoxicity. We used toluene in a combustion reactor with highly controlled conditions to produce two different types of BrC under two conditions corresponding to smoldering and near-flaming combustion, with temperatures of 670 °C and 1035 °C, respectively. We performed online measurements of the size distributions and light-absorption properties of the BrC. The BrC produced at 1035 °C was more light absorbing, with an imaginary component of the refractive index at 532 nm (k532) an order of magnitude larger than that of the BrC produced at 670 °C. We also collected samples for offline chemical characterization using laser desorption ionization (LDI) mass spectrometry. The LDI mass spectra showed that the BrC produced at 1035 °C was composed of species with significantly larger molecular sizes than the BrC produced at 670 °C. Using human lung epithelial cells, we conducted in vitro cytotoxicity analysis on the two types of BrC with doses ranging from 3.5 to 136.0 μg of BrC/ml. After 24-h exposure, the viability of the cells was assessed using a WST-8 assay. The cytotoxicity analysis showed that, for both BrC samples, the cells exhibited a clear dose-dependent response with significant BrC cytotoxicity that plateaued at the higher doses. However, while the viability of cells exposed to the BrC produced at 1035 °C reached a minimum of around 65% at the highest dose, the BrC produced at 670 °C proved to be significantly more toxic, with the viability dropping asymptotically to 25%. The results presented here suggest that organic PM of smaller molecular sizes produced under lower temperature, smoldering combustion could be significantly more toxic than those of larger molecular sizes produced under higher temperature, flaming conditions. The use of a single-molecule fuel in a highly controlled combustion setup distinguishes this work from experiments that rely on real-life sources and combustion setups, where different combustion conditions could be occurring simultaneously and clouding the conclusions.

中文翻译：

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不同燃烧条件下褐碳的理化性质及细胞毒性

摘要 吸光有机颗粒物 (PM) 或褐碳 (BrC) 可能构成燃烧 PM 的重要组成部分。在这里，我们研究了燃烧条件对 BrC 的分子大小、它们的光吸收特性和它们的细胞毒性的影响。我们在燃烧反应器中使用甲苯，在高度受控的条件下，在对应于阴燃和近火焰燃烧的两种条件下，分别生产两种不同类型的 BrC，温度分别为 670 °C 和 1035 °C。我们对 BrC 的尺寸分布和光吸收特性进行了在线测量。在 1035 °C 下产生的 BrC 吸收更多光，在 532 nm (k532) 处的折射率的虚部比在 670 °C 下产生的 BrC 大一个数量级。我们还使用激光解吸电离 (LDI) 质谱法收集了用于离线化学表征的样品。LDI 质谱表明，在 1035 °C 下产生的 BrC 由比在 670 °C 下产生的 BrC 分子尺寸大得多的物质组成。使用人肺上皮细胞，我们对两种类型的 BrC 进行了体外细胞毒性分析，剂量范围为 3.5 至 136.0 μg BrC/ml。暴露 24 小时后，使用 WST-8 测定评估细胞的活力。细胞毒性分析表明，对于两种 BrC 样品，细胞表现出明显的剂量依赖性反应，具有显着的 BrC 细胞毒性，在较高剂量下趋于稳定。然而，虽然暴露于 1035°C 产生的 BrC 的细胞的活力在最高剂量下达到最低约 65%，事实证明，在 670 °C 下产生的 BrC 具有更高的毒性，其生存力逐渐下降至 25%。此处显示的结果表明，在较低温度、阴燃燃烧下产生的较小分子尺寸的有机 PM 可能比在较高温度、燃烧条件下产生的较大分子尺寸的有机 PM 毒性更大。在高度受控的燃烧设置中使用单分子燃料将这项工作与依赖于现实生活中的来源和燃烧设置的实验区分开来，在这些实验中，不同的燃烧条件可能同时发生并使结论变得模糊。阴燃燃烧可能比在较高温度、燃烧条件下产生的较大分子的燃烧毒性更大。在高度受控的燃烧设置中使用单分子燃料将这项工作与依赖于现实生活中的来源和燃烧设置的实验区分开来，在这些实验中，不同的燃烧条件可能同时发生并使结论变得模糊。阴燃燃烧可能比在较高温度、燃烧条件下产生的较大分子的燃烧毒性更大。在高度受控的燃烧设置中使用单分子燃料将这项工作与依赖于现实生活中的来源和燃烧设置的实验区分开来，在这些实验中，不同的燃烧条件可能同时发生并使结论变得模糊。