Department of Chemistry, University of British Columbia, Vancouver, BC V6T 1Z1, Canada.
Laboratory of Environmental Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland.
Proc Natl Acad Sci U S A. 2021 Apr 20;118(16). doi: 10.1073/pnas.2102512118.
Individual atmospheric particles can contain mixtures of primary organic aerosol (POA), secondary organic aerosol (SOA), and secondary inorganic aerosol (SIA). To predict the role of such complex multicomponent particles in air quality and climate, information on the number and types of phases present in the particles is needed. However, the phase behavior of such particles has not been studied in the laboratory, and as a result, remains poorly constrained. Here, we show that POA+SOA+SIA particles can contain three distinct liquid phases: a low-polarity organic-rich phase, a higher-polarity organic-rich phase, and an aqueous inorganic-rich phase. Based on our results, when the elemental oxygen-to-carbon (O:C) ratio of the SOA is less than 0.8, three liquid phases can coexist within the same particle over a wide relative humidity range. In contrast, when the O:C ratio of the SOA is greater than 0.8, three phases will not form. We also demonstrate, using thermodynamic and kinetic modeling, that the presence of three liquid phases in such particles impacts their equilibration timescale with the surrounding gas phase. Three phases will likely also impact their ability to act as nuclei for liquid cloud droplets, the reactivity of these particles, and the mechanism of SOA formation and growth in the atmosphere. These observations provide fundamental information necessary for improved predictions of air quality and aerosol indirect effects on climate.
单个大气粒子可以包含初级有机气溶胶 (POA)、二次有机气溶胶 (SOA) 和二次无机气溶胶 (SIA) 的混合物。为了预测此类复杂多组分粒子在空气质量和气候中的作用，需要了解粒子中存在的相的数量和类型的信息。然而，此类粒子的相行为尚未在实验室中进行研究，因此仍然受到很大限制。在这里，我们表明 POA+SOA+SIA 粒子可以包含三个不同的液相：低极性富有机相、较高极性富有机相和富无机水相。基于我们的结果，当 SOA 的元素氧-碳 (O:C) 比小于 0.8 时，在很宽的相对湿度范围内，同一粒子内可以共存三个液相。相比之下，当 SOA 的 O:C 比大于 0.8 时，三个相将不会形成。我们还通过热力学和动力学建模证明，此类粒子中存在三个液相会影响它们与周围气相达到平衡的时间尺度。三个相也可能会影响它们作为液滴核的能力、这些粒子的反应性以及大气中 SOA 形成和增长的机制。这些观察结果为改善空气质量和气溶胶对气候的间接影响的预测提供了必要的基本信息。
