‡Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
§Aerosol Dynamics Inc., 935 Grayson Street, Berkeley, California 94710, United States.
Environ Sci Technol. 2015 Aug 18;49(16):9768-77. doi: 10.1021/acs.est.5b02115. Epub 2015 Aug 4.
Traditional descriptions of gas-particle partitioning of organic aerosols (OA) rely solely on thermodynamic properties (e.g., volatility). Under realistic conditions where phase partitioning is dynamic rather than static, the transformation of OA involves the interplay of multiphase partitioning with oxidative aging. A key challenge remains in quantifying the fundamental time scales for evaporation and oxidation of semivolatile OA. In this paper, we use isomer-resolved product measurements of a series of normal-alkanes (C18, C20, C22, and C24) to distinguish between gas-phase and heterogeneous oxidation products formed by reaction with hydroxyl radicals (OH). The product isomer distributions when combined with kinetics measurements of evaporation and oxidation enable a quantitative description of the multiphase time scales to be simulated using a single-particle kinetic model. Multiphase partitioning and oxidative transformation of semivolatile normal-alkanes under laboratory conditions is largely controlled by the particle phase state, since the time scales of heterogeneous oxidation and evaporation are found to occur on competing time scales (on the order of 10(-1) h). This is in contrast to atmospheric conditions where heterogeneous oxidation time scales are expected to be much longer (on the order of 10(2) h), with gas-phase oxidation being the dominant process regardless of the evaporation kinetics. Our results demonstrate the dynamic nature of OA multiphase partitioning and oxidative aging and reveal that the fundamental time scales of these processes are crucial for reliably extending laboratory measurements of OA phase partitioning and aging to the atmosphere.
传统的有机气溶胶（OA）气粒分配描述仅依赖于热力学性质（例如挥发性）。在相分配是动态的而不是静态的实际条件下，OA 的转化涉及多相分配与氧化老化的相互作用。一个关键的挑战仍然是量化半挥发性 OA 的蒸发和氧化的基本时间尺度。在本文中，我们使用一系列正构烷烃（C18、C20、C22 和 C24）的异构体分辨产物测量来区分与羟基自由基（OH）反应形成的气相和非均相氧化产物。将产物异构体分布与蒸发和氧化动力学测量相结合，使我们能够使用单个颗粒动力学模型模拟多相时间尺度的定量描述。在实验室条件下，半挥发性正构烷烃的多相分配和氧化转化主要受颗粒相状态控制，因为发现非均相氧化和蒸发的时间尺度发生在竞争时间尺度上（约为 10(-1) h）。这与大气条件形成对比，在大气条件下，非均相氧化时间尺度预计要长得多（约为 10(2) h），无论蒸发动力学如何，气相氧化都是主要过程。我们的结果表明 OA 多相分配和氧化老化的动态性质，并揭示了这些过程的基本时间尺度对于可靠地将 OA 相分配和老化的实验室测量扩展到大气中至关重要。
