Ingram Stephen, Cai Chen, Song Young-Chul, Glowacki David R, Topping David O, O'Meara Simon, Reid Jonathan P
School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK.
Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China.
Phys Chem Chem Phys. 2017 Dec 6;19(47):31634-31646. doi: 10.1039/c7cp05172g.
The physicochemical changes experienced by organic aerosol particles undergoing dehydration into the surrounding gas phase can be drastic, forcing rapid vitrification of the particle and suppressing internal diffusion. Until recently, experimental studies have concentrated on quantifying diffusional mixing of either water or non-volatile components, while relatively little attention has been paid to the role of semivolatile organic component (SVOC) diffusion and volatilisation in maintaining the equilibrium between the gas and particle phases. Here we present methods to simultaneously investigate diffusivities and volatilities in studies of evolving single ternary aerosol particle size and composition. Analysing particles of ternary composition must account for the multiple chemical species that volatilise in response to a step change in gas phase water activity. In addition, treatments of diffusion in multicomponent mixtures are necessary to represent evolving heterogeneities in particle composition. We find that the contributions to observed size behaviour from volatilisation of water and a SVOC can be decoupled and treated separately. Employing Fickian diffusion modelling, we extract the compositional dependence of the diffusion constant of water and compare the results to recently published parametrisations in binary aerosol particles. The treatment of ideality and activity in each case is discussed, with reference to use in multicomponent core shell models. Meanwhile, the evaporation of an SVOC into an unsaturated gas flow may be treated by Maxwell's equation, with slow diffusional transport manifesting as a suppression in the extracted vapour pressure.
经历脱水进入周围气相的有机气溶胶颗粒所经历的物理化学变化可能非常剧烈，迫使颗粒迅速玻璃化并抑制内部扩散。直到最近，实验研究主要集中在量化水或非挥发性成分的扩散混合，而对半挥发性有机成分（SVOC）扩散和挥发在维持气-粒相平衡中的作用关注相对较少。在此，我们展示了在研究不断演变的单个三元气溶胶颗粒大小和组成时同时研究扩散率和挥发性的方法。分析三元组成的颗粒必须考虑到响应气相水活度的阶跃变化而挥发的多种化学物质。此外，处理多组分混合物中的扩散对于描述颗粒组成中不断演变的不均匀性是必要的。我们发现，水和SVOC挥发对观察到的颗粒大小行为的贡献可以解耦并分别处理。采用菲克扩散模型，我们提取了水的扩散常数的组成依赖性，并将结果与最近发表的二元气溶胶颗粒参数化结果进行比较。讨论了每种情况下理想性和活度的处理方法，并参考了其在多组分核壳模型中的应用。同时，SVOC向不饱和气流中的蒸发可以用麦克斯韦方程处理，缓慢的扩散传输表现为提取的蒸气压受到抑制。
