Abstract. Liquid water in cloud droplets and aqueous aerosols serves as an important reaction medium for the formation of secondary aerosol through aqueous-phase reactions (aqSA). Large uncertainties remain in estimates of the production and chemical evolution of aqSA in the dilute solutions found in cloud droplets and the concentrated solutions found in aerosol liquid water, which is partly due to the lack of available measurement tools and techniques. A new oxidation flow reactor (OFR), the Accelerated Production and Processing of Aerosols (APPA) reactor, was developed to measure secondary aerosol formed through gas- and aqueous-phase reactions, both for laboratory gas mixtures containing one or more precursors and for ambient air. For simulating in-cloud processes, droplets formed on monodisperse seed particles are introduced into the top of the reactor and the relative humidity (RH) inside it is controlled to 100 %. Similar measurements made with the RH in the reactor <100 % provide contrasts for aerosol formation with no liquid water and with varying amounts of aerosol liquid water. The reactor was characterized through a series of experiments and used to form secondary aerosol from known concentrations of an organic precursor and from ambient air. The transmission efficiency of O₃ and CO₂ for all RH and of SO₂ for low RH exceeds 90 %, while it falls to about 70 % for SO₂ at 100 % RH. Particle transmission efficiency increases with increasing particle diameter from 0.67 for 0.050 μm particles to 0.98 at 0.20 μm, while that of the ~3.3 μm droplets formed on seed particles is greater than 80 %. The residence time distributions of both gases and particles are narrow relative to other OFRs and lack the tails at long residence time expected with laminar flow. Initial cloud processing experiments focused on the well-studied oxidation of dissolved SO₂ by O₃, with observed growth of seed particles resulting from the added sulfuric acid agreeing well with estimates based on the relevant set of aqueous phase reactions. The OH exposure (OH_exp) for low RH, high RH, and in-cloud conditions was determined experimentally from the loss of SO₂ and benzene, and simulated from the KinSim chemical kinetics solver with inputs of measured 254 nm UV intensity profile through the reactor and loss of O₃ due to photolysis. The aerosol yield for benzene at high OH_exp ranged from 18 % at low RH with dry seed particles present in the reactor to 59 % with cloud droplets present. Measurement of the composition of the secondary aerosol formed from ambient air using an aerosol mass spectrometer showed that the oxygen to carbon ratio (O : C) of the organic component increased with increasing RH (and liquid water content).

中文翻译：

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用于模拟和加速气溶胶液态水和云滴中二次气溶胶形成的氧化流动反应器

摘要。云滴和水性气溶胶中的液态水是通过水相反应 (aqSA) 形成二次气溶胶的重要反应介质。在云滴中发现的稀溶液和气溶胶液态水中发现的浓溶液中，对 aqSA 的产生和化学演化的估计仍然存在很大的不确定性，这部分是由于缺乏可用的测量工具和技术。开发了一种新的氧化流动反应器 (OFR)，即气溶胶的加速生产和加工 (APPA) 反应器，用于测量通过气相和水相反应形成的二次气溶胶，适用于含有一种或多种前体的实验室气体混合物和环境空气。为了模拟云端流程，将单分散种子颗粒上形成的液滴引入反应器顶部，并将其内部的相对湿度 (RH) 控制在 100%。在反应器中 RH <100% 的情况下进行的类似测量提供了在没有液态水和不同量的气溶胶液态水的情况下形成气溶胶的对比。该反应器通过一系列实验进行了表征，并用于从已知浓度的有机前体和环境空气中形成二次气溶胶。O的传输效率 该反应器通过一系列实验进行了表征，并用于从已知浓度的有机前体和环境空气中形成二次气溶胶。O的传输效率 该反应器通过一系列实验进行了表征，并用于从已知浓度的有机前体和环境空气中形成二次气溶胶。O的传输效率_{所有 RH 的 CO 3}和 CO ₂以及低 RH的 SO ₂超过 90 %，而 SO ₂在 100 % RH 时下降到约 70 %。颗粒传输效率随着粒径的增加而增加，从 0.050 μm 颗粒的 0.67 增加到 0.20 μm 的 0.98，而在种子颗粒上形成的约 3.3 μm 液滴的传输效率大于 80%。相对于其他 OFR，气体和颗粒的停留时间分布都较窄，并且缺少层流预期的长停留时间的尾部。最初的云处理实验集中在经过充分研究的 O _{3对溶解的 SO 2的氧化}，观察到的由添加的硫酸引起的种子颗粒的生长与基于相关的水相反应组的估计非常吻合。低 RH、高 RH 和云中条件下的 OH 暴露 (OH _{exp ) 是通过 SO 2}和苯的损失实验确定的，并通过 KinSim 化学动力学求解器进行模拟，输入测量的 254 nm 紫外强度分布通过反应器和由于光解引起的O _3损失。高 OH _{exp下苯的气溶胶产量}范围从反应器中存在干种子颗粒的低相对湿度下的 18% 到存在云滴的 59%。使用气溶胶质谱仪测量由环境空气形成的二次气溶胶的组成表明，有机组分的氧碳比 (O: C) 随着 RH（和液态水含量）的增加而增加。