High-Resolution Mobility and Mass Spectrometry of Negative Ions Produced in a ^sup 241^Am Aerosol Charger

This work concentrates on the simultaneous mobility and mass measurement of negative ions generated by the ionizing radiation in a ^sup 241^Am aerosol charger in N^sub 2^ (5.0), a 1:1-mixture of N^sub 2^ and synthetic air, pure synthetic air (5.0), and filtered laboratory air at ...30% relative humi...

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Bibliographic Details
Published in:Aerosol science and technology 2014-03, Vol.48 (3), p.261
Main Authors: Steiner, Gerhard, Jokinen, Tuija, Junninen, Heikki, Sipilä, Mikko, Petäjä, Tuukka, Worsnop, Douglas, Reischl, Georg P, Kulmala, Markku
Format: Article
Language:English
Subjects:
Aerosols
Humidity
Ions
Mass spectrometry
Measurement
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Summary:This work concentrates on the simultaneous mobility and mass measurement of negative ions generated by the ionizing radiation in a ^sup 241^Am aerosol charger in N^sub 2^ (5.0), a 1:1-mixture of N^sub 2^ and synthetic air, pure synthetic air (5.0), and filtered laboratory air at ...30% relative humidity. Therefore, a high-resolution mobility analyzer (UDMA) and an atmospheric pressure interface time-of-flight mass spectrometer (APi-TOF) were operated in series. Experiments with N2 as carrier gas showed a dominating signal at an electrical mobility of 2.09 cm^sup 2^/Vs with 90% of the ions being nitrate based. The ion composition was altered after a baking-out to a spectrum with three strong mobility-peaks at Z^sub 1^ = 2.34 cm^sup 2^/Vs, Z^sub 2^ = 1.42 cm^sub 2^/Vs, Z^sup 3^ = 1.08 cm^sup 2^/Vs and a higher diversity of ions in the corresponding mass spectra. The carrier gas was gradually changed from N^sub 2^ (5.0) to a 1:1-mixture of N^sub 2^ with synthetic air and pure synthetic air (5.0), having only a minor effect on the overall pattern of the ion spectrum. Using room air leads to a domination of the nitrate based ions. The mobility-dependent transmission efficiency of the UDMA was modeled using an empirical, laminar diffusion deposition model. The data were further compared to an empirical mass-mobility relationship to evaluate the fragmentation of the ion clusters in the inlet of the mass spectrometer. This study suggests that the nitrate ion, NO^sub 3^ -, is found to be the dominant ion species produced in an aerosol charger, and that it may be mostly responsible for the charging of aerosol particles in negative polarity. (ProQuest: ... denotes formulae/symbols omitted.)
ISSN:0278-6826
1521-7388