Abstract
A recently developed Differential Mobility Analyzer (DMA) of high resolving power (50 for ions of mobility equivalent diameter~1 nm) has been used to measure the mobility distribution of laboratory air ions generated by 241Am and corona discharge. In the case of 241Am, it has been possible to follow the changes in mobility during the early stages of ion aging: within the time interval between 10 and 30 ms after ion formation, the mean reduced mobility of positive ions decreased from 1.30 to 1.15 cm^2/Vs, and that of negative ions from 2.0 to 1.75 cm^2/Vs. The mobility distribution of air ions at the outlet of a corona ionizer strongly depends on the corona voltage, mainly due to the mobility-dependent extent of electrostatic losses within the ionizer. The mean reduced mobility of corona ions ranged between 1.01 and 1.20 cm^2/Vs (positive) and 1.76 and 1.96 cm^2/Vs (negative).
Highlights
Particle charging is a process of great importance to the field of aerosol science and technology
We present the results of experimental measurements of mobility distributions of laboratory air ions generated by 241Am and corona discharge, which are among the typical ions usually employed in aerosol charging studies
As previously explained, aging times were estimated as the mean residence time spent by ions in the way between the radioactive source disks and the inlet slit of the Differential Mobility Analyzer (DMA)
Summary
Particle charging is a process of great importance to the field of aerosol science and technology. A different kind of application of particle charging is found in the measurement of the particle size distribution of submicron aerosols by differential mobility analysis. For the latter, one must be able to produce a known and stable charge distribution on the particles (Flagan, 2001). The mechanism of diffusion charging is always at work, even if there is an external electric field, especially in the case of ultrafine aerosol particles (Alguacil and Alonso, 2006)
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