The performance of an electrical ionizer as a bipolar aerosol charger for charging ultrafine particles

Abstract

We developed an aerosol charger that incorporated commercial ionizers to make the setup simple and easily replicated. The built-in high-voltage source for inducing corona discharge embedded in the developed charger (MHM charger) was modulated with pulses so the production of positive and negative ions could be independently regulated. We have studied several attempts to evaluate the performance of the MHM charger as a bipolar charger for charging ultrafine particles. We found that by adjusting the duty-cycle of the modulated pulses, positive and negative ion production is manageable, and the ion concentration depends on the flow rate of the intake air. We used a mini-cyDMA to measure the mobility distribution of positive and negative ions with an average of 1.09 and 1.67 cm2 V−1 s−1, respectively. By utilizing initially charged and neutral particles, we obtained the penetration ratio of both particles: 0.75 and 0.774, respectively. The issue of the MHM charger to generate new particles was also investigated. We found that, on average, the produced new particle concentration was only 5.2 cm−3. In this study, we evaluated the performance of the MHM charger to charge particles by measuring the neutral fraction and charging efficiency. The neutral fraction with particle loss correction follows the established model. The intrinsic and extrinsic charging efficiencies at 100 nm were up to 19% and 41%, respectively. We also assessed the application of the MHM charger in the monodisperse particle generator system. The results showed that the MHM charger could be utilized as an alternative aerosol charger. Copyright © 2021 American Association for Aerosol Research</p