Gao Kunfeng, Koch Hans-Christian, Zhou Chong-Wen, Kanji Zamin A
School of Energy and Power Engineering, Beihang University, Beijing, China.
Shenyuan Honours College of Beihang University, Beihang University, Beijing, China.
Environ Sci Process Impacts. 2022 Nov 16;24(11):2043-2069. doi: 10.1039/d2em00158f.
Aviation soot can affect contrail and cirrus cloud formation and impact climate. A product of incomplete combustion, soot particles, are fractal and hydrophobic aggregates comprising carbonaceous spheres with complex physicochemical properties. In the cirrus cloud regime, the surface wettability and pore abundance of soot particles are important determinants for their ice nucleation ability pore condensation and freezing. In the atmosphere, soot particles can undergo various ageing processes which modify their surface chemistry and porosity, thus acting as ice nucleating particles with varying abilities as a function of ageing. In this study, size-selected soot particles were treated by thermal denuding at 573 K in a pure nitrogen (N) or synthetic air (N + O) flow and then exposed to varying relative humidity conditions at a fixed temperature in the range from 218 to 243 K, to investigate the role of volatile content in the ice nucleation ability. Both organic-lean and organic-rich propane (CH) flame soot particles, as well as two types of commercially available carbon black soot particles with high and low surface wettability, were tested. The size and mass distribution of soot aerosol were monitored during the ice nucleation experiments. Bulk soot samples also prepared in pure N or synthetic air environments at 573 K were characterised by thermogravimetric analysis, Fourier transform infrared spectroscopy and dynamic vapour sorption measurements, to reveal the relation between denuding volatile content, associated soot particle property modifications and the ice nucleation ability. Our study shows that thermal denuding induces a change in soot particle porosity playing a dominant role in regulating its ice nucleation the pore condensation and freezing mechanism. The enrichment in mesopore (2-50 nm) availability may enhance soot ice nucleation. The presence of O in the thermal denuding process may introduce new active sites on soot particles for water interaction and increase soot surface wettability. However, these active sites only facilitate soot ice nucleation when mesopore structures are available. We conclude that a change in volatile content modifies both morphological properties and surface chemistry for soot particles, but porosity change plays the dominant role in regulating soot particle ice nucleation ability.
航空烟尘会影响凝结尾迹和卷云的形成，并对气候产生影响。烟尘颗粒是不完全燃烧的产物，呈分形且具有疏水性，是由具有复杂物理化学性质的碳质球体组成的聚集体。在卷云区域，烟尘颗粒的表面润湿性和孔隙丰度是其冰核形成能力、孔隙凝结和冻结的重要决定因素。在大气中，烟尘颗粒会经历各种老化过程，这些过程会改变其表面化学性质和孔隙率，从而作为具有不同冰核形成能力的冰核颗粒，其能力随老化而变化。在本研究中，对尺寸选择的烟尘颗粒在纯氮（N）或合成空气（N + O）流中于573 K下进行热脱附处理，然后在218至243 K的固定温度下暴露于不同的相对湿度条件下，以研究挥发性成分在冰核形成能力中的作用。测试了贫有机和富有机的丙烷（CH）火焰烟尘颗粒，以及两种具有高和低表面润湿性的市售炭黑烟尘颗粒。在冰核形成实验期间监测烟尘气溶胶的尺寸和质量分布。还通过热重分析、傅里叶变换红外光谱和动态蒸汽吸附测量对在573 K的纯N或合成空气环境中制备的大量烟尘样品进行了表征，以揭示脱附挥发性成分、相关烟尘颗粒性质变化与冰核形成能力之间的关系。我们的研究表明，热脱附会引起烟尘颗粒孔隙率的变化，这在调节其冰核形成（孔隙凝结和冻结机制）中起主导作用。中孔（2 - 50 nm）可用性的增加可能会增强烟尘的冰核形成能力。热脱附过程中O的存在可能会在烟尘颗粒上引入新的与水相互作用的活性位点，并增加烟尘表面润湿性。然而，只有当中孔结构存在时，这些活性位点才会促进烟尘的冰核形成。我们得出结论，挥发性成分的变化会改变烟尘颗粒的形态性质和表面化学性质，但孔隙率变化在调节烟尘颗粒冰核形成能力中起主导作用。
