John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA.
Department of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada.
Nat Commun. 2018 Oct 4;9(1):4076. doi: 10.1038/s41467-018-06622-2.
Hygroscopic growth and cloud condensation nuclei activation are key processes for accurately modeling the climate impacts of organic particulate matter. Nevertheless, the microphysical mechanisms of these processes remain unresolved. Here we report complex thermodynamic behaviors, including humidity-dependent hygroscopicity, diameter-dependent cloud condensation nuclei activity, and liquid-liquid phase separation in the laboratory for biogenically derived secondary organic material representative of similar atmospheric organic particulate matter. These behaviors can be explained by the non-ideal mixing of water with hydrophobic and hydrophilic organic components. The non-ideality-driven liquid-liquid phase separation further enhances water uptake and induces lowered surface tension at high relative humidity, which result in a lower barrier to cloud condensation nuclei activation. By comparison, secondary organic material representing anthropogenic sources does not exhibit complex thermodynamic behavior. The combined results highlight the importance of detailed thermodynamic representations of the hygroscopicity and cloud condensation nuclei activity in models of the Earth's climate system.
吸湿性增长和云凝结核（CCN）激活是准确模拟有机颗粒物气候影响的关键过程。然而，这些过程的微观物理机制仍未得到解决。在这里，我们报告了在实验室中具有复杂热力学行为的生物源次生有机物质，包括湿度依赖性吸湿性、直径依赖性 CCN 活性和液-液相分离。这些行为可以用与疏水性和亲水性有机成分非理想混合的水来解释。非理想混合驱动的液-液相分离进一步增强了水分吸收，并在高相对湿度下诱导表面张力降低，从而降低了 CCN 激活的障碍。相比之下，代表人为来源的次生有机物质则没有表现出复杂的热力学行为。综合结果强调了在地球气候系统模型中对吸湿性和 CCN 活性进行详细热力学描述的重要性。
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