Abstract
Abstract. 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.
Highlights
Aerosol particles can either be emitted into the atmosphere directly from primary sources or generated through the nucleation of atmospheric condensable precursor vapors
In this work we show the development of a nano-scanning electrical mobility spectrometer that features a fast-scanning opposed-migration aerosol classifier (OMAC) and a two-stage condensation particle counter (CPC) to acquire fast and accurate particle size distributions in the range of 1.5– 25 nm
The polydisperse aerosols generated from the hot wire or the atomizer were size-selected by a radial opposedmigration ion and aerosol classifier (ROMIAC) or a cylindrical differential mobility analyzer (DMA) operating at constant voltage to provide a narrow-mobility-distribution sample for nano-scanning electrical mobility spectrometer (nSEMS) calibration
Summary
Aerosol particles can either be emitted into the atmosphere directly from primary sources or generated through the nucleation of atmospheric condensable precursor vapors. The operation of two activation and growth systems in series compounds another challenge to SEMS and SMPS measurements; the residence time within the CPC can distribute counts of particles that exit the DMA over many time bins (Russell et al, 1995; Collins et al, 2002), thereby degrading the resolution of the instrument This effect becomes increasingly important at scan rates that are fast relative to the response time of the CPC. A comparison of nSEMS data with measurements from other wellcalibrated particle sizing instruments at CLOUD confirms its capacity to provide reliable size distribution in the low nanometer size regime
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