Transfer Functions and Penetrations of Five Differential Mobility Analyzers for Sub-2 nm Particle Classification
The transfer functions and penetrations of five differential mobility analyzers (DMAs) for sub-2 nm particle classification were evaluated in this study. These DMAs include the TSI nanoDMA, the Caltech radial DMA (RDMA) and nanoRDMA, the Grimm nanoDMA, and the Karlsruhe-Vienna DMA. Measurements were done using tetra-alkyl ammonium ion standards with mobility diameters of 1.16, 1.47, and 1.70 nm. These monomobile ions were generated by electrospray followed by high resolution mobility classification. Measurements were focused at an aerosol-to-sheath flow ratio of 0.1. A data inversion routine was developed to obtain the true transfer function for each test DMA, and these measured transfer functions were compared with theory. DMA penetration efficiencies were also measured. An approximate model for diffusional deposition, based on the modified Gormley and Kennedy equation using an effective length, is given for each test DMA. These results quantitatively characterize the performance of the test DMAs in classifying sub-2 nm particles and can be readily used for DMA data inversion.
Additional Information© 2011 American Association for Aerosol Research. Received 11 May 2010; accepted 4 August 2010. This work was partially supported by a grant from the US NSF (ATM-0506674) and US DOE (DE-FG-02-05ER63997). JJ thanks Dr. Kenjiro Iida for his help on the data inversion program. A NSF graduate fellowship to NAB is gratefully acknowledged. We thank the two anonymous reviewers for helping to improve the clarity of our article.
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