Vepsäläinen Sampo, Prisle Nønne L
Nano and Molecular Systems Research Unit, University of Oulu, P.O. Box 3000, FI-90014 Oulu, Finland.
Center for Atmospheric Research, University of Oulu, P.O. Box 4500, FI-90014 Oulu, Finland.
Environ Sci Technol. 2025 Jul 22;59(28):14552-14563. doi: 10.1021/acs.est.4c11584. Epub 2025 Jul 10.
Surface active compounds (surfactants) have been found in atmospheric aerosols from many environments. In microscopic aqueous droplets, their presence may cause a variety of effects that are challenging to model comprehensively. In this work, we investigate the solute effects of atmospheric surfactant self-assembly to form micelles and small clusters in aqueous droplets. Several water activity models are employed in combination with Köhler theory to represent self-assembly phenomena within the droplet bulk while also accounting for surfactant bulk-surface partitioning. Our results show that surfactant self-assembly has only minor effects at the critical point of cloud droplet activation; however, very significant effects are observed during earlier stages of droplet growth at subsaturated ambient humidities. A major driver is the binding of free sodium counterions to the surfactant aggregates, strongly limiting the effect of dissolved sodium ions on droplet water activity. Variations in droplet equilibrium size at a given subsaturated humidity due to the presence of surfactant aggregates lead to different estimates of droplet water uptake and aerosol liquid water content. As a result, predictions of atmospheric processes involving surfactant aerosol could be highly sensitive to how surfactant self-assembly and related phenomena are taken into account.
在许多环境的大气气溶胶中都发现了表面活性化合物（表面活性剂）。在微小的水滴中，它们的存在可能会导致各种难以全面建模的效应。在这项工作中，我们研究了大气中表面活性剂自组装在水滴中形成胶束和小聚集体的溶质效应。几种水活度模型与科勒理论相结合，以表示液滴内部的自组装现象，同时也考虑了表面活性剂在本体 - 表面的分配。我们的结果表明，表面活性剂自组装在云滴活化的临界点只有轻微影响；然而，在亚饱和环境湿度下液滴生长的早期阶段观察到非常显著的影响。一个主要驱动因素是游离钠离子与表面活性剂聚集体的结合，这极大地限制了溶解的钠离子对液滴水活度的影响。由于表面活性剂聚集体的存在，在给定的亚饱和湿度下液滴平衡大小的变化导致对液滴吸水量和气溶胶液态水含量的不同估计。因此，涉及表面活性剂气溶胶的大气过程预测可能对如何考虑表面活性剂自组装及相关现象高度敏感。
