Exploring the hygroscopicity, water diffusivity, and viscosity of organic–inorganic aerosols – a case study on internally-mixed citric acid and ammonium sulfate particles
Exploring the hygroscopicity, water diffusivity, and viscosity of organic–inorganic aerosols – a case study on internally-mixed citric acid and ammonium sulfate particles
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探索有机-无机气溶胶的吸湿性、水扩散性和粘度——内部混合柠檬酸和硫酸铵颗粒的案例研究
DOI：
10.1039/d2ea00116k
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发表时间：
2023
期刊：
影响因子：
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通讯作者：
Davies, James F.
中科院分区：
文献类型：
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作者：
Sheldon, Craig S.;Choczynski, Jack M.;Morton, Katie;Palacios Diaz, Teresa;Davis, Ryan D.;Davies, James F.
含有有机分子和无机盐的内部混合气溶胶颗粒普遍存在于大气中，产生于直接排放(例如来自海洋)或有机蒸气与现有无机颗粒种子冷凝产生的间接产物。气溶胶粒子与水蒸气共存，在潮湿的条件下，将以稀水溶液粒子的形式存在，这可以用热力学模型很好地描述。在低湿度条件下，溶质浓度的增加会导致分子相互作用和显著的非理想性效应，这些效应会导致重要物理性质的变化，如粘度和相态，这是使用简单模型无法预测的。在这里，我们探索了一个包含硫酸铵(AS)和柠檬酸(CA)的模型体系。为了更好地了解有机-无机混合物对颗粒特性的影响，我们测量了各种RH条件和有机组分下颗粒的吸湿性、粘度和水分扩散速率。我们报道了这些性质与相对湿度的依赖关系，并探索了将它们联系在一起的常用方法的适用性，如斯托克斯-爱因斯坦关系和热力学模拟方法。结果表明，在较低的相对湿度下，AS的加入导致CA中水含量的减少，如在固定RH处的径向生长因子所示，同时观察到粘度在几个数量级上的增加。与粘度相反，只测量到水扩散的微小变化，用分数斯托克斯-爱因斯坦关系分析表明，由于AS的存在而导致的分子基质的变化可以解释观察到的现象。这项工作表明，少量添加电解质可以导致粒子性质的巨大变化，这意味着将影响环境影响和气溶胶粒子化学的化学反应性、寿命和粒子相。
Internally-mixed aerosol particles containing organic molecules and inorganic salts are prevalent in the atmosphere, arising from direct emission (e.g., from the ocean) or indirect production by condensation of organic vapors onto existing inorganic particle seeds. Aerosol particles co-exist with water vapor and, under humid conditions, will exist as dilute aqueous solution particles that can be well described by thermodynamic models. Under low humidity conditions, the increase in solute concentrations leads to molecular interactions and significant non-ideality effects that drive changes in important physical properties, such as viscosity and phase state, that are not predicted using simple models. Here, we explore a model system containing ammonium sulfate (AS) and citric acid (CA). We measure the hygroscopicity, viscosity, and rate of water diffusion in particles across a range of RH conditions and organic fractions to better understand the influence of organic–inorganic mixtures on particle properties. We report the RH dependence of these properties and explore the applicability of commonly used methods that connect them together, such as the Stokes–Einstein relationship and thermodynamic modelling methods. We show that at low RH, the addition of AS to CA leads to a reduction in the amount of water as indicated by the radial growth factor at a fixed RH, while observing an increase in the viscosity over several orders of magnitude. Contrary to the viscosity, only minor changes in water diffusion were measured, and analysis with the fractional Stokes–Einstein relationship indicates that changes in the molecular matrix due to the presence of AS could explain the observed phenomena. This work reveals that small additions of electrolytes can drive large changes in particle properties, with implications for chemical reactivity, lifetime, and particle phase that will influence the environmental impacts and chemistry of aerosol particles.