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Published August 9, 2021 | Supplemental Material + Published
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The nano-scanning electrical mobility spectrometer (nSEMS) and its application to size distribution measurements of 1.5–25 nm particles


Particle size measurement in the low nanometer regime is of great importance to the study of cloud condensation nuclei formation and to better understand aerosol–cloud interactions. Here we present the design, modeling, and experimental characterization of the nano-scanning electrical mobility spectrometer (nSEMS), a recently developed instrument that probes particle physical properties in the 1.5–25 nm range. The nSEMS consists of a novel differential mobility analyzer and a two-stage condensation particle counter (CPC). The mobility analyzer, a radial opposed-migration ion and aerosol classifier (ROMIAC), can classify nanometer-sized particles with minimal degradation of its resolution and diffusional losses. The ROMIAC operates on a dual high-voltage supply with fast polarity-switching capability to minimize sensitivity to variations in the chemical nature of the ions used to charge the aerosol. Particles transmitted through the mobility analyzer are measured using a two-stage CPC. They are first activated in a fast-mixing diethylene glycol (DEG) stage before being counted by a second detection stage, an ADI MAGIC™ water-based CPC. The transfer function of the integrated instrument is derived from both finite-element modeling and experimental characterization. The nSEMS performance has been evaluated during measurement of transient nucleation and growth events in the CLOUD atmospheric chamber at CERN. We show that the nSEMS can provide high-time- and size-resolution measurement of nanoparticles and can capture the critical aerosol dynamics of newly formed atmospheric particles. Using a soft x-ray bipolar ion source in a compact housing designed to optimize both nanoparticle charging and transmission efficiency as a charge conditioner, the nSEMS has enabled measurement of the contributions of both neutral and ion-mediated nucleation to new particle formation.

Additional Information

© Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License. Received: 04 Mar 2021 – Discussion started: 11 Mar 2021 – Revised: 01 Jul 2021 – Accepted: 01 Jul 2021 – Published: 09 Aug 2021. The authors would like to thank the CLOUD experiment for providing the facility for instrument testing and operation. We gratefully acknowledge a generous gift from Christine and Dwight Landis to improve the data acquisition system of the instrument. This research has been supported by the National Science Foundation (grant nos. 1602086 and 1801329). Review statement: This paper was edited by Charles Brock and reviewed by Juan Fernandez de la Mora and one anonymous referee. Code and data availability: Data and code related to this article are available upon request to the corresponding author. Supplement: The supplement related to this article is available online at: https://doi.org/10.5194/amt-14-5429-2021-supplement. Author contributions: WK wrote the paper, analyzed the data, led the calibration of the instrument, and operated the instrument at CLOUD. SA led the construction the instrument as deployed to CLOUD, developed the data acquisition and control software, contributed to the calibration of the instrument, and contributed to the writing of the paper. HM built and conducted proof-of-concept experiments with the first prototype of the instrument and developed the finite-element simulation in developing the instrument response function. CK developed the soft x-ray charger used in the apparatus and did the initial construction of the two-stage condensation particle counter detector. BCS contributed to the construction and calibration of the instrument and operated it in CLOUD experiments. YH contributed to the development of the data analysis software and contributed to the writing of the paper. GSL developed the modified MAGIC CPC used as the second stage of the detector. SVH led the modifications of the MAGIC CPC for use in this instrument. JHS contributed to the analysis of the data and the writing of the paper. RCF led the project, development of the instrument, design of the experiments, and data analysis, along with contributing to the writing and editing of the paper. Competing interests: The California Institute of Technology has a patent pending for the nSEMS. Aerosol Dynamics Inc. has a patent on the MAGIC CPC. No other conflicts of interest were identified.

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Supplemental Material - amt-14-5429-2021-supplement.pdf


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August 20, 2023
October 20, 2023