Unipolar Air Ions Research Articles

Anti-agglomeration of spark discharge-generated aerosols via unipolar air ions

This paper reports the effect of air ions on the reduction of the agglomeration of metal aerosol particles generated from a homogeneous spark discharge. A carbon fiber ionizer was used to generate air ions near the spark channel formed between two metal electrodes. Once the air ions were generated, particles mixed with ions from the ionizer became charged by random collisions resulting from Brownian motion of the ions. Under the experimental conditions, the particle size right after the spark generation was about 4nm. Then, the size increased to 50nm, 1m downstream (residence time of 1.76s) of the spark channel due to Brownian agglomeration when there were no air ions injected. However, with the injection of air ions (ion concentration: particle concentration=10:1), the size of the particles was reduced to be around 10nm due to the repulsive force between unipolar charged particles with an average charge number of 0.39. In this study, the classical Brownian agglomeration theory for unipolar charged particles was combined with the moment method to predict the particle size distribution as a function of time. The theoretically determined particle size distribution was in good agreement with the size distribution measured using a scanning mobility particle sizer (SMPS) system.

Removal of submicron aerosol particles and bioaerosols using carbon fiber ionizer assisted fibrous medium filter media

This paper reports the installation of a carbon fiber ionizer in front of a fibrous medium filter to enhance the removal of submicron aerosol particles and bioaerosols. Test particles (KCl) were classified with a size range of 50–600 nm using a differential mobility analyzer (DMA). The number concentration of the test particles was measured using a condensation particle counter (CPC). The average charge per particle was estimated by current measurements using an aerosol electrometer. At the face velocity of 0.5 m/s, the particle removal efficiency was 31.4% (for dp=100 nm) when the ionizers were not operating but increased to 35.7% and 46.9% at 1.6×1011ions/s and 6.4×1012ions/s with the ionizers, respectively. For the antibacterial tests, the test bioaerosols (E. coli) were aerosolized using a nebulizer and were deposited on the filter media for 5 minutes. After the deposited bioaerosols were exposed to unipolar air ions, they were incubated for 12 hours. The survival efficiency of E. coli was measured using a colony counting method. The survival fractions of E. coli exposed to positive air ions for 1, 5 and 10 minutes were 61.7%, 45.4% and 25.2%, respectively.

Removal of viable bioaerosol particles with a low-efficiency HVAC filter enhanced by continuous emission of unipolar air ions

Continuous emission of unipolar ions has been shown to improve the performance of respirators and stationary filters challenged with non-biological particles. In this study, we investigated the ion-induced enhancement effect while challenging a low-efficiency heating, ventilation and air-conditioning (HVAC) filter with viable bacterial cells, bacterial and fungal spores, and viruses. The aerosol concentration was measured in real time. Samples were also collected with a bioaerosol sampler for viable microbial analysis. The removal efficiency of the filter was determined, respectively, with and without an ion emitter. The ionization was found to significantly enhance the filter efficiency in removing viable biological particles from the airflow. For example, when challenged with viable bacteria, the filter efficiency increased as much as four- to fivefold. For viable fungal spores, the ion-induced enhancement improved the efficiency by a factor of approximately 2. When testing with virus-carrying liquid droplets, the original removal efficiency provided by the filter was rather low: 9.09 +/- 4.84%. While the ion emission increased collection about fourfold, the efficiency did not reach 75-100% observed with bacteria and fungi. These findings, together with our previously published results for non-biological particles, demonstrate the feasibility of a new approach for reducing aerosol particles in HVAC systems used for indoor air quality control. Recirculated air in HVAC systems used for indoor air quality control in buildings often contains considerable number of viable bioaerosol particles because of limited efficiency of the filters installed in these systems. In the present study, we investigated - using aerosolized bacterial cells, bacterial and fungal spores, and virus-carrying particles - a novel idea of enhancing the performance of a low-efficiency HVAC filter utilizing continuous emission of unipolar ions in the filter vicinity. The findings described in this paper, together with our previously published results for non-biological particles, demonstrate the feasibility of the newly developed approach.

Evaluation of ionic air purifiers for reducing aerosol exposure in confined indoor spaces

Numerous techniques have been developed over the years for reducing aerosol exposure in indoor air environments. Among indoor air purifiers of different types, ionic emitters have gained increasing attention and are presently used for removing dust particles, aeroallergens and airborne microorganisms from indoor air. In this study, five ionic air purifiers (two wearable and three stationary) that produce unipolar air ions were evaluated with respect to their ability to reduce aerosol exposure in confined indoor spaces. The concentration decay of respirable particles of different properties was monitored in real time inside the breathing zone of a human manikin, which was placed in a relatively small (2.6 m3) walk-in chamber during the operation of an ionic air purifier in calm air and under mixing air condition. The particle removal efficiency as a function of particle size was determined using the data collected with a size-selective optical particle counter. The removal efficiency of the more powerful of the two wearable ionic purifiers reached about 50% after 15 min and almost 100% after 1.5 h of continuous operation in the chamber under calm air conditions. In the absence of external ventilation, air mixing, especially vigorous one (900 CFM), enhanced the air cleaning effect. Similar results were obtained when the manikin was placed inside a partial enclosure that simulated an aircraft seating configuration. All three stationary ionic air purifiers tested in this study were found capable of reducing the aerosol concentration in a confined indoor space. The most powerful stationary unit demonstrated an extremely high particle removal efficiency that increased sharply to almost 90% within 5-6 min, reaching about 100% within 10-12 min for all particle sizes (0.3-3 microm) tested in the chamber. For the units of the same emission rate, the data suggest that the ion polarity per se (negative vs. positive) does not affect the performance but the ion emission rate does. The effects of particle size (within the tested range) and properties (NaCl, PSL, Pseudomonas fluorescens bacteria) as well as the effects of the manikin's body temperature and its breathing on the ionic purifier performance were either small or insignificant. The data suggest that the unipolar ionic air purifiers are particularly efficient in reducing aerosol exposure in the breathing zone when used inside confined spaces with a relatively high surface-to-volume ratio. Ionic air purifiers have become increasingly popular for removing dust particles, aeroallergens and airborne microorganisms from indoor air in various settings. While the indoor air cleaning effect, resulting from unipolar and bipolar ion emission, has been tested by several investigators, there are still controversial claims (favorable and unfavorable) about the performance of commercially available ionic air purifiers. Among the five tested ionic air purifiers (two wearable and three stationary) producing unipolar air ions, the units with a higher ion emission rate provided higher particle removal efficiency. The ion polarity (negative vs. positive), the particle size (0.3-3 microm) and properties (NaCl, PSL, Pseudomonas fluorescens bacteria), as well as the body temperature and breathing did not considerable affected the ionization-driven particle removal. The data suggest that the unipolar ionic air purifiers are particularly efficient in reducing aerosol exposure in the breathing zone when they are used inside confined spaces with a relatively high surface-to-volume ratio (such as automobile cabins, aircraft seating areas, bathrooms, cellular offices, small residential rooms, and animal confinements). Based on our experiments, we proposed that purifiers with a very high ion emission rate be operated in an intermittent mode if used indoors for extended time periods. As the particles migrate to and deposit on indoor surfaces during the operation of ionic air purifiers, some excessive surface contamination may occur, which introduces the need of periodic cleaning these surfaces.

Filtering Efficiency of N95- and R95-Type Facepiece Respirators, Dust-Mist Facepiece Respirators, and Surgical Masks Operating in Unipolarly Ionized Indoor Air Environments

The emission of unipolar air ions in the vicinity of a filtering facepiece respirator has been recently shown to considerably enhance its respiratory protection efficiency. The effect is driven by the electric repelling forces that develop between the unipolarly charged mask and the aerosol particles, thus creating a shield for the incoming particles and consequently decreasing the penetration efficiency through the filter. The manikin-based preliminary evaluation of this concept has been performed with a very limited number of variables. In this study, four types of half-mask facepiece filtering devices (N95, R95, and dust-mist respirators, as well as surgical masks), operating at two different breathing flow rates, were tested with unipolar air ion emitters exhibiting different emission rates and polarities. The particle penetration efficiency through the facepiece filter was determined in a room-size indoor test chamber by a real-time particle size selective aerosol monitoring performed inside and outside of the mask, which was face-sealed onto a manikin. Three commercially available ionic air purifiers were utilized as air ion emitters. For the targeted particle size range of ~0.04 – 1.3 μm, a 12- minute air ionization in the vicinity of a manikin enhanced the respiratory mask performance by a factor ranging from 1.61 to 3,250, depending on the respirator type, breathing flow rate, and the ion emission rate. The effect was achieved primarily within the first 3 minutes.

AN ELECTROSTATIC METHOD OF DRYING SALINE WATER

ABSTRACT Times for drying and nucleation of saline solutions exposed to relatively high fluxes of unipolar air ions, produced by corona electrodes, were studied with a beta-ray gauge. Ion-treated solutions of NaCl of various concentrations dried about 3.2 times faster when exposed to either 2.54 x 1012;positive or 4.42 x 1012 negative air ions cm-2 s-1 than the control samples. The nucleation site in a solution was observed to be directly below the emitting electrode; whereas nucleation appeared to be spatially random for untreated solutions. The solutions nucleated earlier when treated with the ion fluxes than the control. Electric wind caused by the ionic drag is proposed as the principal driving force for the enhancement of the drying process. The phenomenon of elctrostriction might have also aided in nucleating the solutions.

A novel technique for drying soil samples

Abstract Evaporation rates and drying times of soil samples exposed to high fluxes of unipolar air ions of either polarity, produced by corona electrodes, were studied with a beta‐ray gauge. Ion‐treated soils dried more than three times faster than the control samples under the same laboratory conditions. An analysis of the experimental curves on Rideau clay showed evaporation rates of 2.96 x 10‐4and 8.84 x 10‐4g cm‐2min‐1for control and treated samples, respectively, when exposed to 4.39 x 1012negative air ions cm‐2s‐1. An objective criterion was defined for a state of soil dryness when the sample acquired a steady‐state value of transmission of beta particles with time. Electric wind caused by the ionic drag is proposed as the principal driving force for the enhancement of evaporation rates from soil samples used.

Impact of air ions on mass transfer from liquids

Evaporation rates and drying times of liquids exposed to relatively high fluxes of unipolar air ions of either sign, produced by corona electrodes, were studied with a beta-ray gauge apparatus. Liquids of constant volume, exposed to air ions, dried 1.72 to 4.80 times faster than the corresponding control liquids under the same laboratory conditions. An analysis of the time-transmission curves from the beta-ray gauge showed mass transfer rates of 1.90 × 10 −3 and 8.5 × 10 −3 g min −1 for control and treated (2.44 × 10 12 positive ions cm −2 s −1) water, respectively. Air ions were observed to cause circulatory and vibrational movements in the treated liquids. These movements contributed to the enhancement in the mass transfer rates from organic and inorganic liquids studied. Polarity of the molecules may also determine the rapidity at which a liquid will evaporate when exposed to a high flux of air ions.

Tracer experiments with turbulently dispersed air ions

Unipolar air ions released into the wind constitute a tracer which can be measured with high resolution. An ion source produces a cloud with homogeneous charge density, insensitive to source strength, dependent on time since formation only. It is well suited for tracing concentration changes due to turbulence, less suited for cloud size tracing.

Characterization of aerosol mobility distributions by integral mobility analysis—the method of mobility moments

A procedure was developed for generating moments of aerosol mobility distributions using the charged particle precipitation properties of the low pass (integral) mobility analyzer. Application of the moment technique was demonstrated through two types of experiments using nearly monodisperse polystyrene particles. In one set of experiments a measurement of the first and second moments of the mobility distribution for singly charged polystyrene particles was used to infer the mean particle size and size standard deviation for two different Dow polystyrene latex batches. The size measurements were found to be in agreement with several other independent sizing studies. In a separate experiment the first two mobility moments were used to characterize the distribution of electric charge on an aerosol of polystyrene particles exposed to unipolar air ions. Mean aerosol charge and charge standard deviations were determined by the moment method and by a simpler, but less rigorous technique in which analyzer mobility resolution was assumed to be ideal. The mean charge and charge standard deviation measured by the two methods were found to be in good agreement, even though analyzer mobility resolution was only 10 per cent

The influence of unipolar air ions on the electrophoretic mobility of erythrocytes.

Positive air ions decreased the electrophoretic mobility of erythrocytes of cats while negative air ions increased it. Inhalation of normal air supplied by a fan did not affect the electrophoretic mobility of erythrocytes.

EFFECTS OF EXPERIMENTALLY ALTERED UNIPOLAR AIR-ION DENSITY UPON THE AMOUNT OF ACTIVITY OF THE BLOWFLY, CALLIPHORA VICINA R.D.

Populations of the blowfly, Calliphora vicina R.D., were exposed to different densities of artificially produced unipolar air-ions. The activity of the flies was continuously recorded. Increased positive-ion densities resulted in increased flight activity. With a moderately high positive-ion density the peak activity occurred approximately 0.75 hours after first exposure to the ions. Following the peak, the activity returned to the original level while the insects were still exposed to the ions. No activity effect was observed with the negative-ion density level used.

Effects of unipolar air ions on microorganisms and on evaporation

Bacteria in droplets of distilled water were exposed to unipolar atmospheric ions produced by radioisotopes. Experiments using micro-chemical equipment and bacteriological techniques were carried out both in clean and contaminated air. Lethal results in clean air were attributed primarily to the action of ions on staphylococci. Survival in contaminated air was attributed primarily to the action of contaminants in shielding the staphylococci from (high mobility) ions. Evaporation rates were found to differ according to the presence, or absence, of air ions and atmospheric pollutants.

Protective and lethal effects of unipolar air ions on microorganisms

Protective and lethal effects of unipolar air ions on microorganisms