专栏名称: Carbon Research

An international multidisciplinary platform for communicating advances in fundamental and applied research on carbon.

ES&T | 大气棕碳的气粒分配与粘性研究新视角

Carbon Research · 公众号 · 化学 · 2024-11-03 00:00

正文

大气棕碳的气粒分配与粘性研究新视角

Molecular Insights into Gas–Particle Partitioning and Viscosity of Atmospheric Brown Carbon

来源

索引

Molecular Insights into Gas–Particle Partitioning and Viscosity of Atmospheric Brown Carbon, Environ. Sci. Technol. 2024, 58, 41, 18284–18294

下载PDF文件（仅供学术交流）

Molecular Insights into Gas–Particle Partitioning and Viscosity of Atmospheric Brown Carbon.pdf

文章摘要

近日美国普渡大学化学系与地球大气行星科学系的一项研究揭示，生物质燃烧产生的有机气溶胶（BBOA），包含棕色碳发色团，在大气化学和气候强迫中起着关键作用。然而，不同环境条件下蒸发对BBOA挥发性和粘度的影响仍未被充分理解。美国的研究团队通过木材热解排放实验生成了实验室BBOA模型，并对这些模型进行了深入的分子表征。研究人员对初始的“热解油（PO1）”进行了逐步蒸发，得到浓度逐渐升高的混合物（PO1.33、PO2和PO3），相应的体积减少系数为1.33、2和3。研究团队结合温度程序解吸（TPD）、实时直接离子化分析和高分辨率质谱（DART-HRMS），对这些不同状态下的化学组分和挥发性特征进行了详细分析。该创新性方法量化了各个组分的饱和蒸气压和焓值，构建了挥发性基础分布，并量化了气-粒分配情况。通过“针刺流动实验”验证的粘度估算表明，随着蒸发的进行，粘度显著增加，导致粒子相扩散速度减慢，平衡时间延长。研究结果表明，老化的生物质燃烧排放中，高粘度的“焦油球”粒子形成是由于半挥发性成分的蒸发。这项研究强调了蒸发过程在塑造BBOA性质中的重要性，指出了在大气模型中纳入这些因素的必要性，以更好地预测BBOA的老化及其环境影响。

要点图例

Figure 1 (a, b) Progression of (−)DART-HRMS spectra of PO1 (a) and PO3 (b) samples averaged over annotated temperature ranges of the TPD experiment. The temperature profile (red line) is shown along the second y-axis of the plot. The relative abundances of the individual peaks are arbitrarily scaled to the cubic root of the corresponding MS peak relative intensities to facilitate the comparison. (c, d) Arrhenius plots of ln(IT – IT0) versus 1/T (K–1) of three selected species of C6H8O3, C11H12O4, and C16H18O4. Orange symbols denote linear regions used to fit (red dashed lines) the data using Clausius–Clapeyron equation and calculate the apparent enthalpies of solid-to-gas transitions, shown in legends. The color scale reflects viscosity values calculated for each species as a function of temperature during the TPD run.

Figure 2 (a–c) Volatility basis set (VBS) distributions for components of the PO1 mixture considering an atmospheric cooling down process of biomass burning emissions exemplified by decreasing temperatures (473, 373, and 298 K) and constant organic mass (tOM) loadings of 1000 μg m–3. (d–f) VBS distributions for components of the PO1 sample mixture considering atmospheric dilution exemplified by decreasing values of tOM loadings (1000, 100, and 10 μg m–3) and a temperature of 298 K. Light colors denote the portions of PO1 components capable of gas-phase partitioning under these conditions. Pie charts depict the estimated mass fraction percent of gas-phase and particle-phase species summed across all VBS bins.

Figure 3 Particle-phase mass fractions calculated for the aerosolized PO1 components using the constructed VBS distributions and considering broad ranges of ambient temperatures and total organic mass (tOM) loadings. Dash lines showcase the rapid cooling trajectory (blue line) versus gradual cooling trajectory (red line).

Figure 4 (a, b) Comparison of the VBS distributions constructed for PO1 and PO3 mixtures under conditions of T = 298 K and tOM = 100 μg m–3. Pie charts depict the estimated mass fraction percent of total gas- and particle-phase species summed across all VBS bins. (c, d) The same VBS distributions as shown above, incorporating information on viscosity values calculated for individual components identified in the mixtures. The viscosity values of individual components are segmented into a series of groups with viscosity ranges that differ by a factor of 10. Each bin in the VBS distributions is color-coded to represent contributions of components with varying viscosity ranges. The color bar denotes the viscosity ranges, with reference materials indicated on the left.

Figure 5 (a) Comparison of viscosity values computed for POx mixtures based on the constructed VBS distributions and Tg(ωorg) values derived from elemental formulas and VTF equation, (32,33) those derived from C* values, (38) and experimental viscosity values derived from the poke-flow measurements conducted at room temperature. The dashed line in the plot indicates a polynomial fit of the computed POx viscosity values, parametrized as log(η) = 1.39x2 + 8.56x – 3.90 (R2 = 0.99). (b) Viscosity and e-folding times computed for 200 nm particles composed of POx mixtures and water content equilibrated at different levels of RH at room temperature.

文章结论

研究人员通过实验数据构建了不同温度下的挥发性基础集（VBS）分布，分析了生物质燃烧有机气溶胶（BBOA）在大气冷却和稀释过程中的气-颗粒分配特性。研究发现，在冷却过程中，BBOA的低挥发性成分更多地转入颗粒相，而在大气稀释过程中，部分颗粒成分会逐渐转移至气相，这种转变对BBOA的老化和粘度变化产生了重要影响。研究表明，大气温度和有机物负荷等环境条件显著影响了BBOA的气-颗粒分配及其光学特性。进一步了解这些挥发性和物理性质变化对大气化学和气候的影响，将有助于预测BBOA的环境行为及其对全球辐射强迫的贡献。。