Ohno Paul E, Brandão Lilliana, Rainone Elizabeth M, Aruffo Eleonora, Wang Junfeng, Qin Yiming, Martin Scot T
School of Engineering and Applied Sciences & Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, United States.
Harvard University Center for the Environment, Cambridge, Massachusetts 02138, United States.
J Phys Chem A. 2023 Apr 6;127(13):2967-2974. doi: 10.1021/acs.jpca.2c08224. Epub 2023 Mar 22.
Liquid-liquid phase separation (LLPS) of atmospheric particles impacts a range of atmospheric processes. Driven by thermodynamics, LLPS occurs in mixed organic-inorganic particles when high inorganic salt concentrations exclude organic compounds, which develop into a separate phase. The effect of particle size on the thermodynamic and kinetic drivers of LLPS, however, remains incompletely understood. Here, the size dependence was studied for the separation relative humidity (SRH) of LLPS. Submicron organic-inorganic aerosol particles of ammonium sulfate mixed with 1,2,6-hexanetriol and polyethylene glycol (PEG) were studied. In a flow configuration, upstream size selection was coupled to a downstream fluorescence aerosol flow tube (F-AFT) at 293 ± 1 K. For both mixed particle types, the SRH values for submicron particle diameters of 260-410 nm agreed with previous measurements reported in the literature for supermicron particles. For smaller particles, the SRH values decreased by approximately 5% RH for diameters of 130-260 nm for PEG-sulfate particles and of 70-190 nm for hexanetriol-sulfate particles. From these observations, the nucleation rate in the hexanetriol-sulfate system was constrained, implying an activation barrier to nucleation of +1.4 to +2.0 × 10 J at 70% RH and 293 K. Quantifying the activation barrier is an approach for predicting size-dependent LLPS in the atmosphere.
大气颗粒物的液-液相分离（LLPS）影响一系列大气过程。在热力学驱动下，当高无机盐浓度排斥有机化合物时，LLPS会在有机-无机混合颗粒中发生，这些有机化合物会形成一个单独的相。然而，颗粒大小对LLPS的热力学和动力学驱动因素的影响仍未完全理解。在此，研究了LLPS的分离相对湿度（SRH）对颗粒大小的依赖性。研究了与1,2,6-己三醇和聚乙二醇（PEG）混合的硫酸铵亚微米有机-无机气溶胶颗粒。在流动配置中，上游尺寸选择与293±1 K下的下游荧光气溶胶流管（F-AFT）相连。对于两种混合颗粒类型，260-410 nm亚微米颗粒直径的SRH值与文献中报道的超微米颗粒的先前测量值一致。对于较小的颗粒，PEG-硫酸盐颗粒直径为130-260 nm时，SRH值降低了约5%RH，己三醇-硫酸盐颗粒直径为70-190 nm时，SRH值也降低了约5%RH。根据这些观察结果，限制了己三醇-硫酸盐系统中的成核速率，这意味着在70%RH和293 K下成核的活化能垒为 +1.4至 +2.0 × 10 J。量化活化能垒是预测大气中与尺寸相关的LLPS的一种方法。
