Nonideal molecular interactions in aerosol particles influence the partitioning of semivolatile organic compounds (SVOCs). However, few direct measurements exist that determine activity coefficients (γ), which quantify nonideality, for individual organic compounds in different atmospheric mixtures. By measuring the isothermal evaporation of SOA formed from multifunctional SVOCs in an environmental chamber, this study determines the mole-fraction-based γ of the bulk SOA in a variety of pre-existing chemically complex particles, approximated as if the bulk SOA behaved like a single SVOC. These multicomponent mixtures contain molecular structures commonly found in the atmosphere. When treated as a single liquid phase, γ of the bulk SOA tends to increase from ∼1 to ∼5 as the organic seeds and the SOA have more differing polarities. A high computed γ value of 74 for a wet ammonium sulfate-SOA system indicates phase separation. The γ for some individual species was also quantified based on gas-phase measurements and AIOMFAC model predictions. However, the bulk SOA γ cannot be explained by the simplified speciated SVOC–seed interactions, suggesting incomplete compositional understanding of the bulk SOA. These results demonstrate a method to quantify nonideal behavior and show that it can occur in multicomponent mixtures and therefore influence OA formation, evolution, and lifetimes.

中文翻译：

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通过实验室室内的等温蒸发确定SOA的活性系数

气溶胶颗粒中的非理想分子相互作用会影响半挥发性有机化合物（SVOC）的分配。但是，很少有直接测量方法可以确定不同大气混合物中单个有机化合物的活性系数（γ），该系数可量化非理想性。通过测量在环境室中由多功能SVOC形成的SOA的等温蒸发，本研究确定了各种预先存在的化学复杂粒子中，本体SOA的基于摩尔分数的γ，近似于本体SOA的行为类似于单一SVOC。这些多组分混合物包含通常在大气中发现的分子结构。当作为单一液相处理时，块状SOA的γ倾向于从〜1增加到〜5，这是因为有机晶种和SOA具有更多不同的极性。湿硫酸铵-SOA系统的高γ计算值74表示相分离。还根据气相测量和AIOMFAC模型预测对某些单个物种的γ进行了定量。但是，大量的SOAγ不能通过简化的指定SVOC-种子相互作用来解释，这表明对大量SOA的成分了解不完整。这些结果证明了一种量化非理想行为的方法，并表明它可以在多组分混合物中发生，因此影响OA的形成，演化和寿命。表示对批量SOA的组成了解不完整。这些结果证明了一种量化非理想行为的方法，并表明它可以在多组分混合物中发生，因此影响OA的形成，演化和寿命。表示对批量SOA的组成了解不完整。这些结果证明了一种量化非理想行为的方法，并表明它可以在多组分混合物中发生，因此影响OA的形成，演化和寿命。