Modelling ultrafine particle growth in a flow tube reactor
Modelling ultrafine particle growth in a flow tube reactor
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DOI：
10.5194/amt-15-4663-2022
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发表时间：
2022-08
影响因子：
3.8
通讯作者：
Michael S. Taylor Jr.;Devon N. Higgins;M. Johnston
中科院分区：
文献类型：
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作者：
Michael S. Taylor Jr.;Devon N. Higgins;M. Johnston
抽象。流管反应器常用于研究气溶胶动力学。本研究的目的是探讨如何最好地代表复杂的生长动力学的超细颗粒在流管反应器中的化学过程引起的颗粒生长是未知的。在典型的流管实验中，测量入口和出口颗粒尺寸分布以给出生长的时间平均测量，如果生长动力学随着颗粒通过流管而改变，则这可能难以解释。在这项工作中，我们模拟颗粒生长的二次有机气溶胶（SOA）的形成，结合表面和体积有限的化学过程，以说明如何复杂的增长动力学内的流管可以出现。然后，我们开发和评估一种方法来解释复杂的生长动力学时，驱动动力学的化学过程是未知的。颗粒的直径增长由增长因子（GF）表示，增长因子（GF）定义为在特定时间段期间生长颗粒的来自挥发性有机化合物（VOC）前体的氧化的产物的分数。以这种方式定义，GF是冷凝生长颗粒的所有非挥发性产物加上一部分半挥发性分子的总和，所述半挥发性分子在所研究的时间范围内在颗粒上或颗粒中反应以产生保留在颗粒中的非挥发性产物。相对于流管测量，GF是独立的壁损失和冷凝槽，影响颗粒生长动力学，并可以从实验到实验。GF被示出为在流管内作为时间的函数而变化，并且对影响生长的因素敏感，所述因素例如是前体的气相混合比和在颗粒的表面上或体积中的气溶胶液态水（ALW）的存在。提出了一种从流管实验中的出口减去入口颗粒直径变化来计算GF的方法，并示出了从SOA形成的模拟来精确地匹配GF。
Abstract. Flow tube reactors are often used to study aerosol kinetics. The goal of this study is to investigate how to best represent complex growth kinetics of ultrafine particles within a flow tube reactor when the chemical processes causing particle growth are unknown. In a typical flow tube experiment, one measures the inlet and outlet particle size distributions to give a time-averaged measure of growth, which may be difficult to interpret if the growth kinetics change as particles transit through the flow tube. In this work, we simulate particle growth for secondary organic aerosol (SOA) formation that incorporates both surface- and volume-limited chemical processes to illustrate how complex growth kinetics inside a flow tube can arise. We then develop and assess a method to account for complex growth kinetics when the chemical processes driving the kinetics are not known. Diameter growth of particles is represented by a growth factor (GF), defined as the fraction of products from oxidation of the volatile organic compound (VOC) precursors that grow particles during a specific time period. Defined in this way, GF is the sum of all non-volatile products that condensationally grow particles plus a portion of semi-volatile molecules that react on or in the particle to give non-volatile products that remain in the particle over the investigated time frame. With respect to flow tube measurements, GF is independent of wall loss and condensation sink, which influence particle growth kinetics and can vary from experiment to experiment. GF is shown to change as a function of time within the flow tube and is sensitive to factors that affect growth such as gas-phase mixing ratios of the precursors and the presence of aerosol liquid water (ALW) on the surface or in the volume of the particle. A method to calculate GF from the outlet-minus-inlet particle diameter change in a flow tube experiment is presented and shown to accurately match GFs from simulations of SOA formation.