Steiner G, Franchin A, Kangasluoma J, Kerminen V-M, Kulmala M, Petäjä T
Institute for Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria.
Faculty of Physics, University of Vienna, Wien, Austria.
Aerosol Sci Technol. 2017 Aug 3;51(8):946-955. doi: 10.1080/02786826.2017.1328103. Epub 2017 May 8.
Measuring aerosols and molecular clusters below the 3 nm size limit is essential to increase our understanding of new particle formation. Instruments for the detection of sub-3 nm aerosols and clusters exist and need to be carefully calibrated and characterized. So far calibrations and laboratory tests have been carried out using mainly electrically charged aerosols, as they are easier to handle experimentally. However, the charging state of the cluster is an important variable to take into account. Furthermore, instrument characterization performed with charged aerosols could be biased, preventing a correct interpretation of data when electrically neutral sub-3 nm aerosols are involved. This article presents the first steps to generate electrically neutral molecular clusters as standards for calibration. We show two methods: One based on the neutralization of well-known molecular clusters (mobility standards) by ions generated in a switchable aerosol neutralizer. The second is based on the controlled neutralization of mobility standards with mobility standards of opposite polarity in a recombination cell. We highlight the challenges of these two techniques and, where possible, point out solutions. In addition, we give an outlook on the next steps toward generating well-defined neutral molecular clusters with a known chemical composition and concentration. Published with license by American Association for Aerosol Research.
测量尺寸小于3纳米的气溶胶和分子团簇对于增进我们对新粒子形成的理解至关重要。用于检测亚3纳米气溶胶和团簇的仪器已经存在，并且需要仔细校准和表征。到目前为止，校准和实验室测试主要使用带电气溶胶进行，因为它们在实验上更易于操作。然而，团簇的带电状态是一个需要考虑的重要变量。此外，使用带电气溶胶进行的仪器表征可能存在偏差，当涉及电中性亚3纳米气溶胶时，会妨碍对数据的正确解读。本文介绍了生成电中性分子团簇作为校准标准的初步步骤。我们展示了两种方法：一种基于在可切换气溶胶中和器中产生的离子对知名分子团簇（迁移率标准）的中和。第二种基于在复合池中用相反极性的迁移率标准对迁移率标准进行受控中和。我们强调了这两种技术的挑战，并在可能的情况下指出解决方案。此外，我们展望了朝着生成具有已知化学成分和浓度的明确中性分子团簇的下一步进展。由美国气溶胶研究协会授权发布。
