New particle formation (NPF) produces about 50% of the global cloud condensation nuclei in the troposphere. As such, NPF plays a crucial role in climate. Despite advancements in instrumentation capable of measuring freshly formed aerosol particles down to ~ 1 nm in diameter, the mechanisms behind NPF remain understudied due to the complex composition and chemistry of the atmosphere. Nucleation is the first step of NPF and involves gaseous precursors reacting to form stable clusters; consequently, it is essential to understand the reaction kinetics behind nucleation reactions. Controlled laboratory experiments have previously been used to examine these reactions, which can occur at extremely low reactant concentrations (i.e., parts per quadrillion level, 10⁵ cm⁻³) or lower. Nucleation experiments require pristine conditions for the reactions to proceed without interference from unpredictable contaminants. Here, a low-cost flow reactor is presented that minimizes contamination and allows for nucleation kinetics to be observed. The layout and setup of an example reactor are presented with a brief discussion on how to operate the reactor to ensure cleanliness and repeatability. In addition, methods for quantifying nucleation reactants as well as analytical measurement techniques to adequately measure nucleation kinetics in this flow reactor system are described. This experimental protocol can be employed to characterize nucleation reactions that can ultimately be used to develop nucleation models important for predicting how aerosol particles influence climate.

新的粒子形成（NPF）产生了对流层约50％的全球云凝结核。因此，NPF在气候中起着至关重要的作用。尽管可以测量直径约1 nm以下的新鲜形成的气溶胶颗粒的仪器有所进步，但由于大气的复杂成分和化学性质，NPF背后的机理仍未得到充分研究。成核是NPF的第一步，涉及气态前体反应形成稳定的团簇。因此，了解成核反应背后的反应动力学至关重要。以前已经使用受控的实验室实验来检查这些反应，这些反应可以在极低的反应物浓度下发生（即，每个四氢呋喃含量为10 ⁵  cm ^{-3的部分）}）或更低。成核实验需要原始条件才能使反应进行，且不受不可预测的污染物的干扰。在这里，提出了一种低成本的流动反应器，其使污染最小化并且允许观察到成核动力学。介绍了示例反应器的布局和设置，并简要讨论了如何操作反应器以确保清洁度和可重复性。另外，描述了定量成核反应物的方法以及分析测量技术以充分测量该流动反应器系统中的成核动力学。该实验方案可用于表征成核反应，该反应最终可用于开发对预测气溶胶颗粒如何影响气候非常重要的成核模型。