Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States.
Chemical Sciences Division, Lawrence Berkeley National Lab, Berkeley, California 94720, United States.
J Phys Chem A. 2022 Aug 4;126(30):4991-5010. doi: 10.1021/acs.jpca.2c03059. Epub 2022 Jul 21.
Chemical transformations in aerosols impact the lifetime of particle phase species, the fate of atmospheric pollutants, and both climate- and health-relevant aerosol properties. Timescales for multiphase reactions of ozone in atmospheric aqueous phases are governed by coupled kinetic processes between the gas phase, the particle interface, and its bulk, which respond dynamically to reactive consumption of O. However, models of atmospheric aerosol reactivity often do not account for the coupled nature of multiphase processes. To examine these dynamics, we use new and prior experimental observations of aqueous droplet reaction kinetics, including three systems with a range of surface affinities and ozonolysis rate coefficients (-aconitic acid (CHO), maleic acid (CHO), and sodium nitrite (NaNO)). Using literature rate coefficients and thermodynamic properties, we constrain a simple two-compartment stochastic kinetic model which resolves the interface from the particle bulk and represents O partitioning, diffusion, and reaction as a coupled kinetic system. Our kinetic model accurately predicts decay kinetics across all three systems, demonstrating that both the thermodynamic properties of O and the coupled kinetic and diffusion processes are key to making accurate predictions. An enhanced concentration of adsorbed O, compared to gas and bulk phases is rapidly maintained and remains constant even as O is consumed by reaction. Multiphase systems dynamically seek to achieve equilibrium in response to reactive O loss, but this is hampered at solute concentrations relevant to aqueous aerosol by the rate of O arrival in the bulk by diffusion. As a result, bulk-phase O becomes depleted from its Henry's law solubility. This bulk-phase O depletion limits reaction timescales for relatively slow-reacting organic solutes with low interfacial affinity (i.e., -aconitic and maleic acids, with ≈ 10-10 M s), which is in contrast to fast-reacting solutes with higher surface affinity (i.e., nitrite, with ≈ 10 M s) where surface reactions strongly impact the observed decay kinetics.
气溶胶中的化学转化会影响颗粒相物质的寿命、大气污染物的归宿，以及与气候和健康相关的气溶胶特性。在大气水相中的臭氧多相反应的时间尺度受气相、颗粒界面及其本体之间的耦合动力学过程控制，这些过程会对 O 的反应性消耗做出动态响应。然而，大气气溶胶反应性模型通常没有考虑多相过程的耦合性质。为了研究这些动力学，我们利用新的和先前的关于水相液滴反应动力学的实验观测结果，包括三个具有不同表面亲和力和臭氧分解速率系数（-巴豆酸（CHO）、马来酸（CHO）和亚硝酸钠（NaNO））的体系。我们使用文献中的速率系数和热力学性质来约束一个简单的两隔间随机动力学模型，该模型将界面与颗粒本体区分开来，并将 O 的分配、扩散和反应表示为一个耦合的动力学系统。我们的动力学模型准确地预测了所有三个体系的衰减动力学，这表明 O 的热力学性质以及耦合的动力学和扩散过程对于做出准确的预测都是关键的。与气相和本体相相比，吸附 O 的浓度迅速增加并保持恒定，即使 O 被反应消耗也是如此。多相体系会动态地寻求在 O 反应性损失的情况下达到平衡，但在与水相气溶胶相关的溶液浓度下，扩散导致 O 到达本体的速率限制了这种平衡的达成。结果，本体相中的 O 耗尽了其亨利定律溶解度。这种本体相 O 耗竭限制了与低界面亲和力的相对慢反应有机溶质（即，-巴豆酸和马来酸，其 ≈ 10-10 M s）的反应时间尺度，这与具有较高表面亲和力的快速反应溶质（即，亚硝酸盐，其 ≈ 10 M s）形成对比，在这种情况下，表面反应强烈影响观察到的衰减动力学。
