Aging aerosol in a well-mixed continuous flow tank reactor: An introduction of the activation time distribution

Abstract. Simulating atmospheric aging processes in the laboratory under atmospheric conditions typically requires large aerosol chambers (several m3) in order to achieve extended observation times. We developed an experimental approach that enables long observation times in small chamber volumes by operating the aerosol chamber in a Continuous Flow Stirred Tank Reactor (CSTR) mode. We present a mathematical framework which allows the retrieval of data beyond calculating mean values using the newly introduced metric activation time (tact). This concept was developed and successfully tested to characterize the change in cloud condensation nuclei (CCN) activity of soot particles due to heterogeneous oxidation with ozone. We show that this concept can be applied to other systems investigating non-gradual transitions. The change in CCN-activity was parameterized with tact and agreed well with theoretical predictions. Furthermore we show how tact can be applied for the analysis of data originating from other oxidation flow reactors widely used in atmospheric sciences. This concept allows to explain discrepancies found in intercomparison of different chambers.

摘要。在实验室环境下模拟大气老化过程时，通常需要使用体积达数立方米的大型气溶胶室，以获取足够长的观测时长。我们开发了一种实验方法，通过将气溶胶室以连续流搅拌槽式反应器（Continuous Flow Stirred Tank Reactor, CSTR）模式运行，可在较小的腔室体积内实现较长的观测时间。我们提出了一套数学分析框架，借助新引入的度量指标活化时间（activation time, t_act），不仅可计算平均值，还能提取更多维度的有效数据。该概念已得到开发与验证，可用于表征臭氧非均相氧化作用下，烟尘颗粒云凝结核（cloud condensation nuclei, CCN）活性的变化。我们证实，该概念可推广应用于其他研究非渐进转变过程的实验系统。研究中，我们以活化时间为参数对云凝结核活性的变化进行参数化处理，结果与理论预测吻合良好。此外，我们还阐明了如何将活化时间应用于分析大气科学领域广泛使用的各类氧化流动反应器所产生的实验数据。该概念可用于解释不同气溶胶室相互比对实验中出现的结果不一致问题。