ABSTRACT A cavity ring-down spectrometer and condensation particle counter were used to investigate the limitations in the separation of singly and multiply charged aerosol particles by a tandem differential mobility analyzer (DMA) and aerosol particle mass analyzer (APM). The impact of particle polydispersity and morphology was investigated using three materials: nearly monodisperse polystyrene latex nanospheres (PSL); polydisperse, nearly spherical ammonium sulfate (AS), and polydisperse lacey fractal soot agglomerates. PSL and AS particles were easily resolved as a function of charge. For soot, the presence of multiply charged particles severely affects the isolation of the singly charged particles. In cases where the DMA–APM was unable to fully resolve the singly charged particles of interest, the peak mass deviated by up to 13% leading to errors in the mass specific extinction cross section of over 100%. For measurements of nonspherical particles, nonsymmetrical distributions of concentration as a function of mass were a sign of the presence of multiply charged particles. Under these conditions, the effects of multiply charged particles can be reduced by using a second charge neutralizer after the DMA and prior to the APM. Dilution of the aerosol stream serves to decrease the total number concentration of particles and does not remove the contributions of multiply charged particles.

中文翻译：

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串联微分迁移率分析仪-气溶胶颗粒质量分析仪分离气溶胶的实际局限性

摘要 使用空腔衰荡光谱仪和冷凝粒子计数器来研究串联差分迁移率分析仪 (DMA) 和气溶胶粒子质量分析仪 (APM) 分离单电荷和多电荷气溶胶粒子的局限性。使用三种材料研究了颗粒多分散性和形态的影响：几乎单分散的聚苯乙烯乳胶纳米球 (PSL)；多分散、近球形硫酸铵 (AS) 和多分散花边分形烟灰团聚体。PSL 和 AS 粒子很容易被解析为电荷的函数。对于烟尘，多带电粒子的存在严重影响单带电粒子的分离。在 DMA-APM 无法完全分辨目标单电荷粒子的情况下，峰值质量偏差高达 13%，导致质量比消光截面的误差超过 100%。对于非球形粒子的测量，作为质量函数的非对称浓度分布是多带电粒子存在的标志。在这些条件下，可以通过在 DMA 之后和 APM 之前使用第二个电荷中和剂来减少多带电粒子的影响。气溶胶流的稀释用于降低粒子的总数浓度并且不会去除多带电粒子的贡献。通过在 DMA 之后和 APM 之前使用第二个电荷中和器，可以减少多带电粒子的影响。气溶胶流的稀释用于降低粒子的总数浓度并且不会去除多带电粒子的贡献。通过在 DMA 之后和 APM 之前使用第二个电荷中和器，可以减少多带电粒子的影响。气溶胶流的稀释用于降低粒子的总数浓度并且不会消除多带电粒子的贡献。