Schmidt-Ott Fabian, Maisser Anne, Biskos George
Climate and Atmosphere Research Centre, The Cyprus Institute, Nicosia 2121, Cyprus.
Institute for Atmospheric and Earth System Research, University of Helsinki, Helsinki 00014, Finland.
Anal Chem. 2024 Sep 10;96(36):14405-14412. doi: 10.1021/acs.analchem.4c01796. Epub 2024 Aug 26.
Positive and negative ions produced by radioactive sources and corona discharges in gases find a number of applications, including charging aerosol particles prior to their measurement by electrical and/or electrical mobility techniques. The degree to which these ions can charge aerosol particles depends on their mobility and mass; properties that are strongly affected by the composition of the carrier gas and the impurities that it contains. We show that when the purity of the carrier gas is increased, the mobility of both positive and negative ions increases by more than 50%, whereas the respective masses reduce by more than 50%. In most cases, the dominant positive species is N, whereas NO and NO prevail for the negative polarity. Differences in ion mobility and mass resulting from the two ionization methods (i.e., radioactive source and corona discharges) remain limited. When volatile methyl siloxanes (VMS) are introduced deliberately to the gas, the mobility of the cations decreases by 39% and their mass increases by 385%, while the dominant mobility and mass peaks of the negative ions remains almost unaffected. Interestingly, introduction of VMS also leads to consistent and reproducible positive ion properties across all variations of the experiments, which can be especially relevant for charging aerosol particles in a reproducible manner. Taken together, the new measurements we report in this paper corroborate prior knowledge that the composition and purity of the carrier gas strongly influence the properties of positive and negative ions generated in aerosol neutralizers, and provide new evidence regarding their evolution in the presence of impurities.
由放射性源和气体中的电晕放电产生的正离子和负离子有许多应用，包括在通过电学和/或电迁移率技术测量气溶胶颗粒之前对其进行充电。这些离子对气溶胶颗粒充电的程度取决于它们的迁移率和质量；这些特性会受到载气成分及其所含杂质的强烈影响。我们表明，当载气纯度提高时，正离子和负离子的迁移率均增加超过50%，而各自的质量减少超过50%。在大多数情况下，主要的正离子种类是N⁺，而对于负极性，NO⁻和NO₂⁻占主导。两种电离方法（即放射性源和电晕放电）导致的离子迁移率和质量差异仍然有限。当故意将挥发性甲基硅氧烷（VMS）引入气体中时，阳离子的迁移率降低39%，其质量增加385%，而负离子的主要迁移率和质量峰值几乎不受影响。有趣的是，引入VMS还会在所有实验变化中导致一致且可重复的正离子特性，这对于以可重复的方式对气溶胶颗粒充电可能特别重要。综上所述，我们在本文中报告的新测量结果证实了先前的知识，即载气的成分和纯度会强烈影响气溶胶中和器中产生的正离子和负离子的特性，并提供了关于它们在存在杂质时演变的新证据。
