A novel high-resolution small ion spectrometer to study ion nucleation of aerosols in ambient indoor and outdoor air

AP Fews, NK Holden, PA Keitch, DL Henshaw

Research output: Contribution to journalArticle (Academic Journal)peer-review

17 Citations (Scopus)

Abstract

An electrically based ion spectrometer is described, capable of measuring particle sizes and mobilities from molecular ions (small ions) to aerosol particles across a size range of 0.4 to 30 nm in diameter. It consists of a single cylindrical capacitor divided into three electrically insulated sections. The current arriving at the central section is measured by an electrometer and represents the ion flux over a known range of mobilities determined by the applied voltage. The applied voltage is scanned in steps to measure the ion fluxes over a large number of overlapping mobility ranges. The recorded signal and the response function of the instrument are unfolded using a maximum entropy procedure to give a high-resolution measured mobility spectrum. The maximum entropy approach offers a considerable improvement over traditional aspiration collectors and can approach the resolution of a drift tube system. In this way, the spectrometer successfully overcomes the diffusion limit to small ion resolution. Illustrative spectra are shown, demonstrating for the first time the presence of some resolved structure within the small ion spectrum at the highest mobilities. It is demonstrated that the actual mobility spectrum of small ions falls in the range 0.8–2.0 × 10−4 m2 V−1 s−1. This represents a narrower range than that previously measured which is attributed to improved spectral resolution in the present work.
Translated title of the contributionA novel high-resolution small ion spectrometer to study ion nucleation of aerosols in ambient indoor and outdoor air
Original languageEnglish
Pages (from-to)29 - 48
Number of pages20
JournalAtmospheric Research
Volume76
Publication statusPublished - 2005

Bibliographical note

Publisher: Elsevier Science

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