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Ion–Aerosol Flux Coefficients and the Steady-State Charge Distribution of Aerosols in a Bipolar Ion Environment

Lόpez-Yglesias, Xerxes and Flagan, Richard C. (2013) Ion–Aerosol Flux Coefficients and the Steady-State Charge Distribution of Aerosols in a Bipolar Ion Environment. Aerosol Science and Technology, 47 (6). pp. 688-704. ISSN 0278-6826. doi:10.1080/02786826.2013.783684.

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Fuchs’ theory, as corrected by Hoppel and Frick, is widely used to compute flux coefficients of ions to aerosol particles and the resultant charge distribution. We have identified approximations made in previous works that limit the theory’s accuracy. Hoppel and Frick used two characteristic speeds or kinetic energies to calculate the flux coefficients of ions to aerosol particles in lieu of an average of the flux coefficients over the Maxwell–Boltzmann distribution of ion speeds. In the present work, we show that this approximation artificially reduces the number of multiply charged particles. Ion capture may be enhanced by three-body trapping, a process wherein an ion has a collision with a neutral gas molecule and loses sufficient kinetic energy to be captured by the particle. The gas kinetic theory approach to three-body trapping has been refined to better account for the collision between the ion and a neutral gas molecule within the potential presented by the particle. Approximations to the calculation of energy losses and the probability of ion capture have been relaxed. The possibility that an image charge may be induced on the ion as well as on the particle is allowed. While the previous work was limited to electrically conductive particles, both the ion and the particle are allowed to have any dielectric constant in the present work, and the finite size of the ions is taken into account when calculating minimum capture radii for the ion–particle interactions. The resulting ion flux coefficients differ from previous results both in the low nanometer regime and in the continuum regime. We explore the influence of key parameters on the charge distribution, including dielectric constant, temperature, and pressure, to understand how operating conditions may affect the interpretation of differential mobility analyzer measurements of particle size distributions. Finally, an empirical expression for the new charge distribution is given to facilitate rapid calculations.

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Flagan, Richard C.0000-0001-5690-770X
Additional Information:© 2013 American Association for Aerosol Research. Received: 17 Jan 2012. Accepted: 08 Oct 2012. Accepted author version posted online: 12 Mar 2013. Published online: 08 Apr 2013. The authors thank Lindsay Yee for her time spent editing and discussing this manuscript. They would also like to thank an anonymous reviewer for doing an outstanding job; the reviewer raised interesting scientific points that go well beyond the scope of the current work. Finally, the authors thank the NASA Astrobiology Institute through the NAI Titan team managed at JPL under NASA Contract NAS7-03001 for the funding of this project, and the Ayrshire Foundation for their support in making computing resources available.
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Issue or Number:6
Record Number:CaltechAUTHORS:20130510-090712962
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Official Citation:Ion–Aerosol Flux Coefficients and the Steady-State Charge Distribution of Aerosols in a Bipolar Ion Environment Xerxes López-Yglesias & Richard C. Flagan pages 688-704
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38414
Deposited By: Ruth Sustaita
Deposited On:10 May 2013 16:26
Last Modified:09 Nov 2021 23:37

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