Abstract Electrical mobility and mass of atmospheric ions are of great importance, since both properties jointly determine their charging states. In this work, different carrier gases of bottle N2, bottle air, and particle-free lab air were passed through a TSI® soft X-ray aerosol neutralizer to produce both positive and negative ions. The electrical mobilities and mass-to-charge ratios of these ions were measured with a high-resolution half-mini differential mobility analyzer (DMA) coupled to an atmospheric pressure interface time-of-flight (APi-TOF) mass spectrometer. The effects of carrier gas, sample flowrate, and relative humidity (RH) on the ion mobility and mass-to-charge ratio were evaluated. Most detected ions could be traced back to the impurities in the carrier gases, or the compounds used to manufacture the system components. However, severe fragmentation of DMA-classified clusters was observed, especially under high RH conditions, which likely occurred inside the APi-TOF and complicated the identification of the chemical composition of the DMA-classified clusters. The mobility spectra and ion identities were comparable when using bottle N2 and bottle air as the carrier gas, whereas different features on ion mobility and mass-to-charge ratio were found in the case of particle-free lab air. Residence time of the carrier gas inside the neutralizer as a function of the sample flowrate, when at the order of a few seconds, exerted a weak impact on the ion mobility spectra. The effect of RH on the electrical mobility was contingent on the polarity and chemical composition of ions. The presence of water vapor would grow the acid radical ions and hydronium ions to larger sizes by forming clusters, whereas the positively charged polydimethylsiloxanes in the case of particle-free lab air were marginally impacted. In addition, the concentration of neutral clusters formed through the ion-ion recombination or radiolysis was measured with a particle size magnifier (PSM). Compared with those in the case of bottle gases, the neutral cluster concentrations were significantly larger when particle-free lab air was used as the carrier gas. Higher concentrations of neutral clusters were observed in the high RH experiments, likely because high RH could either enhance the ion-ion recombination or the detection efficiency of PSM. Our work indicates that RH and the impurities in the carrier gas have a significant effect on the measured electrical mobilities and mass spectra for ions generated by a soft X-ray aerosol neutralizer.

中文翻译：

---

商用软 X 射线气溶胶中和器产生的离子的尺寸分辨化学成分分析

摘要 大气离子的电迁移率和质量非常重要，因为这两种特性共同决定了它们的充电状态。在这项工作中，瓶 N2、瓶空气和无颗粒实验室空气的不同载气通过 TSI® 软 X 射线气溶胶中和器以产生正离子和负离子。这些离子的电迁移率和质荷比是用高分辨率半微型微分迁移率分析仪 (DMA) 与大气压界面飞行时间 (APi-TOF) 质谱仪耦合测量的。评估了载气、样品流速和相对湿度 (RH) 对离子迁移率和质荷比的影响。大多数检测到的离子可以追溯到载气中的杂质，或用于制造系统组件的化合物。然而，观察到 DMA 分类簇的严重碎片，特别是在高 RH 条件下，这可能发生在 APi-TOF 内部，并使 DMA 分类簇的化学成分鉴定变得复杂。当使用瓶 N2 和瓶空气作为载气时，迁移谱和离子特性具有可比性，而在无颗粒实验室空气的情况下发现离子迁移率和质荷比的不同特征。载气在中和器内的停留时间作为样品流速的函数，当在几秒钟的数量级时，对离子迁移谱产生微弱的影响。RH 对电迁移率的影响取决于离子的极性和化学成分。水蒸气的存在会通过形成簇使酸根离子和水合氢离子增长到更大的尺寸，而在无颗粒实验室空气的情况下，带正电的聚二甲基硅氧烷受到的影响很小。此外，通过离子-离子复合或辐射分解形成的中性簇的浓度用粒度放大镜 (PSM) 测量。与瓶装气体相比，当使用无颗粒实验室空气作为载气时，中性簇浓度明显更高。在高 RH 实验中观察到更高浓度的中性簇，可能是因为高 RH 可以增强离子 - 离子重组或 PSM 的检测效率。