Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States.
Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 76100, Israel.
Environ Sci Technol. 2024 Apr 30;58(17):7493-7504. doi: 10.1021/acs.est.3c10184. Epub 2024 Apr 18.
Samples of brown carbon (BrC) material were collected from smoke emissions originating from wood pyrolysis experiments, serving as a proxy for BrC representative of biomass burning emissions. The acquired samples, referred to as "pyrolysis oil (PO)," underwent subsequent processing by thermal evaporation of their volatile compounds, resulting in a set of three additional samples with volume reduction factors of 1.33, 2, and 3, denoted as PO, PO, and PO. The chemical compositions of these PO samples and their BrC chromophore features were analyzed using a high-performance liquid chromatography instrument coupled with a photodiode array detector and a high-resolution mass spectrometer. The investigation revealed a noteworthy twofold enhancement of BrC light absorption observed for the progression of PO to PO samples, assessed across the spectral range of 300-500 nm. Concurrently, a decrease in the absorption Ångstrom exponent (AAE) from 11 to 7 was observed, indicating a weaker spectral dependence. The relative enhancement of BrC absorption at longer wavelengths was more significant, as exemplified by the increased mass absorption coefficient (MAC) measured at 405 nm from 0.1 to 0.5 m/g. Molecular characterization further supports this darkening trend, manifesting as a depletion of small oxygenated, less absorbing monoaromatic compounds and the retention of relatively large, less polar, more absorbing constituents. Noteworthy alterations of the PO to PO mixtures included a reduction in the saturation vapor pressure of their components and an increase in viscosity. These changes were quantified by the mean values shifting from approximately 1.8 × 10 μg/m to 2.3 μg/m and from ∼10 Pa·s to ∼10 Pa·s, respectively. These results provide quantitative insights into the extent of BrC aerosol darkening during atmospheric aging through nonreactive evaporation. This new understanding will inform the refinement of atmospheric and chemical transport models.
从木材热解实验产生的烟雾排放中采集了棕色碳（BrC）物质样本，作为代表生物质燃烧排放的 BrC 的代表。获得的样本称为“热解油（PO）”，随后通过其挥发性化合物的热蒸发进行后续处理，得到三个额外的样本，体积缩减因子分别为 1.33、2 和 3，分别表示为 PO、PO 和 PO。使用高效液相色谱仪与光电二极管阵列检测器和高分辨率质谱仪分析了这些 PO 样本的化学组成及其 BrC 发色团特征。研究表明，随着 PO 向 PO 样本的进展，观察到 BrC 光吸收增加了两倍，在 300-500nm 的光谱范围内进行评估。同时，观察到吸收 Ångstrom 指数（AAE）从 11 降低到 7，表明光谱依赖性减弱。在较长波长处 BrC 吸收的相对增强更为显著，例如在 405nm 处测量的质量吸收系数（MAC）从 0.1 增加到 0.5m/g。分子特征进一步支持了这种变暗趋势，表现为较小的含氧、吸收性较弱的单芳烃化合物的耗尽以及相对较大、非极性、吸收性较强的成分的保留。PO 向 PO 混合物的显著变化包括其成分的饱和蒸气压降低和粘度增加。这些变化通过平均值从大约 1.8×10μg/m 转移到 2.3μg/m 和从大约 10Pa·s 转移到大约 10Pa·s 来量化。这些结果通过非反应性蒸发提供了对大气老化过程中 BrC 气溶胶变暗程度的定量见解。这种新的理解将为大气和化学输送模型的改进提供信息。
