We introduce the CMC based Ionic Surfactant Activity model (CISA) to calculate activity coefficients in ternary aqueous solutions of an ionic surfactant and an inorganic salt. The surfactant can be either anionic or cationic and in the present development, the surfactant and inorganic salts share a common counterion. CISA incorporates micellization into the Pitzer–Debye–Hückel (PDH) framework for activities of mixed electrolyte solutions. To reduce computing requirements, a parametrization of the critical micelle concentration (CMC) is used to estimate the degree of micellization instead of explicit equilibrium calculations. For both binary and ternary systems, CISA only requires binary experimentally-based parameters to describe water–ion interactions and temperature–composition dependency of the CMC. The CISA model is intended in particular for atmospheric applications, where higher-order solution interaction parameters are typically not constrained by experiments and the description must be reliable across a wide range of compositions. We evaluate the model against experimental activity data for binary aqueous solutions of ionic surfactants sodium octanoate and sodium decanoate, as common components of atmospheric aerosols, and sodium dodecylsulfate, the most commonly used model compound for atmospheric surfactants. Capabilities of the CISA model to describe ternary systems are tested for the water–sodium decanoate–sodium chloride system, a common surrogate for marine background cloud condensation nuclei and to our knowledge the only atmospherically relevant system for which ternary activity data is available. For these systems, CISA is able to provide continuous predictions of activity coefficients both below and above CMC and in all cases gives an improved description of the water activity above the CMC, compared to the alternative model of Burchfield and Wolley [J. Phys. Chem., 88(10), 2149–2155 (1984)]. The water activity is a key parameter governing the formation and equilibrium growth of cloud droplets. The CISA model can be extended from the current form to include the effect of other inorganic salts with the existing database of binary PDH parameters and using appropriate mixing rules to account for ion specificity in the micellization process.

我们引入基于 CMC 的离子表面活性剂活度模型 (CISA)来计算离子表面活性剂和无机盐三元水溶液中的活度系数。表面活性剂可以是阴离子或阳离子的，并且在本发明中，表面活性剂和无机盐共享共同的抗衡离子。 CISA 将胶束化纳入混合电解质溶液活性的 Pitzer-Debye-Hückel (PDH) 框架中。为了减少计算要求，使用临界胶束浓度 (CMC) 的参数化来估计胶束化程度，而不是明确的平衡计算。对于二元和三元系统，CISA 仅需要基于实验的二元参数来描述 CMC 的水-离子相互作用和温度-成分依赖性。 CISA 模型特别适用于大气应用，其中高阶溶液相互作用参数通常不受实验限制，并且描述必须在各种成分中可靠。我们根据离子表面活性剂辛酸钠和癸酸钠（作为大气气溶胶的常见成分）和十二烷基硫酸钠（大气表面活性剂最常用的模型化合物）的二元水溶液的实验活性数据来评估模型。 CISA 模型描述三元系统的能力针对水-癸酸钠-氯化钠系统进行了测试，该系统是海洋背景云凝结核的常见替代品，并且据我们所知，这是唯一可获得三元活动数据的大气相关系统。对于这些系统，与 Burchfield 和Wolley的替代模型相比，CISA 能够提供低于和高于 CMC 的活度系数的连续预测，并且在所有情况下都能对高于 CMC 的水分活度进行改进的描述。化学。，88（10），2149-2155（1984）]。水活度是控制云滴形成和平衡生长的关键参数。 CISA 模型可以从当前形式扩展为包括其他无机盐与现有二元 PDH 参数数据库的影响，并使用适当的混合规则来解释胶束化过程中的离子特异性。