We present measurements of the isothermal evaporation of α-pinene ozonolysis secondary organic aerosol (SOA). Using a novel, filter-based method, we reproduce literature observations of the time-dependent evaporation of SOA particles. We apply two detailed physical models to interpret the evaporative behavior of both the bulk SOA and individual components. Both models find that a combination of effectively nonvolatile products, together with reversibly formed oligomers (or otherwise reactive monomers) having a decomposition lifetime of 9 to 28 h, best explains the evolution of composition and volatility as particles age in the absence of both organic vapors and oxidants, even under an assumption of relatively viscous (soft wax-like with a minimum diffusion coefficient of 1 × 10^–15 cm² s^–1) particles. We find that the residence time in the SOA formation chamber and time spent undergoing isothermal evaporation, both indicative of the physical age of the aerosol, are the most important experimental parameters determining the evaporation rate. The evolution of volatility observed in these experiments is compared to field measurements in a boreal forest site. The ambient monoterpene-dominated SOA volatility is only reproduced in the laboratory after 24 h of extended aging in a dilute, dark, oxidant-free environment.

中文翻译：

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α-P烯臭氧分解SOA的等温蒸发：挥发性，相态和低聚物组成

我们目前对α-pine烯臭氧分解二次有机气溶胶（SOA）的等温蒸发进行测量。使用基于过滤器的新颖方法，我们再现了SOA颗粒随时间变化的蒸发的文献观察。我们应用两个详细的物理模型来解释大容量SOA和单个组件的蒸发行为。两种模型都发现，有效的非挥发性产物与可逆形成的低聚物（或反应性单体）的分解寿命为9至28小时的组合，可以最好地解释在不存在两种有机蒸气的情况下，随着颗粒老化而形成的组成和挥发性和氧化剂，即使在相对粘性的假设下（软蜡状，最小扩散系数为1×10 ^–15 cm ²s ^–1）粒子。我们发现，在SOA形成室中的停留时间和经历等温蒸发所花费的时间，均指示了气溶胶的物理年龄，是决定蒸发速率的最重要的实验参数。将这些实验中观察到的挥发性演变与北方森林地带的实地测量进行了比较。仅在稀，黑暗，无氧化剂的环境中长时间老化24小时后，才能在实验室中再现环境单萜为主的SOA挥发性。