Snake Ions: Does Bi-polar Ionization Really Work Against Gas-Phase Contaminants?  Just as snake eyes are a losing proposition at the craps table in a casino, using bi-polar ionization to control airborne contaminants can have the same outcome – nothing to show for your money. The simple answer to this question is a qualified “maybe,” in that there may be some effect against gas-phase contaminants when using a bi-polar ionization system, but only as a result of unintended consequences - the uncontrolled production of ozone.
Whether it’s called ozone or “trivalent oxygen,” “activated oxygen,” “oxygen radicals,” “free radicals,” “(super-) atomic oxygen,” “monoatomic oxygen,” “oxygen clusters,” or by some other name, the fact remains that any effect on gas-phase contaminants by bi-polar ionization would be due to an oxidation process. This is the same process we use with our Purafil Select and Purafil SP media products, but in a controlled and predictable manner. We know how much active oxidant is contained in the media, how it works against specific types of contaminants, and we can predict how long it will last before replacement is necessary. The same cannot be said for the ozone produced by bi-polar ionization systems. How Bi-polar Ionization Systems Work
Bi-polar Ionization systems are devices integrating two electrodes into what is commonly referred to as an “ionization tube.” When an electrical current as high as 2500V is applied between the two electrodes, electrons start moving from one air molecule to another, so producing positive and negative air ions, by a process call corona discharge . This association/dissociation process has been depicted graphically by one manufacturer and is shown in Figure 1. 
Figure 1. The bi-polar ionization process. At higher voltages (≥5000V), these devices start dissociating the oxygen molecules (O2 = 2O*), and begin building up concentrations of ozone in the local environment (O2 + O* = O3). Ozone Production by Bi-polar Ionization Systems
Chemically, ozone is one of the strongest known oxidizing agents that rapidly react with many substances. It is classified as an irritant and can lead to irritation and long term damage to the respiratory system and lungs. Persons especially vulnerable include children, the elderly and persons with asthma and respiratory disease. Frequent symptoms of ozone exposure include coughing, chest tightness, and shortness of breath. Bi-polar ionization systems generate considerably less ozone than dedicated ozone generators, but can still raise indoor ozone levels enough to cause concern about potential human exposure. Almost all manufacturers of these systems acknowledge the production of ozone. Some actually list ozone production levels (see below) while others only offer generalized statements such as “Low ozone generation – well below acceptable level.” | Ozone concentration generated by unit | No more than 0.03 mg/m3 (or 15.29 ppb, the average daily MAC[1] for atmospheric air) | | NO2 concentration generated by unit[2] | No more than 0.04 mg/m3 (or 21.27 ppb, the average daily MAC for atmospheric air) | In a paper authored by Stephen H. Zitin, founder and President of Bioclimatic, Inc. – a major supplier of bi-polar ionization systems, he states: “Ozone is a by-product of any ionization process or high voltage field. When operated in accordance with manufacturer’s instructions, non-detectable concentrations of ozone will result.” However, we can only guess just what is meant by “non-detectable concentrations.” Another manufacturer states that “…as long as the ozone concentration stays below 100 ppb, there is no danger.” Danger to whom or what? Given that the most commonly cited acceptable human exposure level for ozone is 50 ppb, a device that gives off 100 ppb would have to be considered totally unacceptable for human exposure. It is interesting to note that the background concentrations of ozone at sea level in clean air vary between 15 and 25 ppb. Therefore, these devices may only produce a maximum of 25 ppb to be within the safe limits. Many researchers conclude that ozone concentrations within safe operating limits will not produce significant removal efficiencies of contaminants by contact oxidation. They believe that ozone serves to “mask” odors instead of removing them in these applications due to ozone's ability to desensitize the olfactory apparatus so that the odors can no longer be perceived. The U.S. EPA and the American Lung Association have issued several warnings and publications alerting consumers that certain types of indoor air cleaners can generate potentially harmful concentrations of ozone. These air cleaning devices are generically referring as ozone-generating air purifiers – although they may not be directly marketed as such. They are also marketed as “energized or activated oxygen” or “pure air” devices. How much ozone is actually produced by a bi-polar ionization system is not only an issue from the perspective of an exposed person, but also from the perspective of just what, if any effect such a system may have the control of gas-phase contaminants. Bi-polar Ionization for Gas-Phase Air Cleaning
Bi-polar air ionization can be effective at removing particulates (they agglomerate into larger particles) when used in conjunction with standard particulate filtration. It is also effective for neutralizing static electric charges, e.g. in the semiconductor industry where various processes generate static charges that can damage microelectronic components. However, many manufacturers directly market this technology as a stand-alone technology for gas-phase air purification and odor control and this is where it has severe limitations. According to Mr. Zitin some of the limitations of the bi-polar ionization association / dissociation process include: -
It depends on electrostatic attraction. -
VOCs and odors are oxidized to CO2 and H2O; but only a limited number are controlled, e.g. lighter molecular weight hydrocarbons and unsaturated compounds. -
Typical single pass efficiencies are 20% to 40% depending on the chemicals. -
Ozone is a byproduct and requires proper system control to maintain ozone at safe background levels. Additional considerations, from Dr. Stacy L. Daniels, Research Director for Precision Air include: -
Systems need to be well engineered; proper operation should be certified, and performance should be validated. -
Upstream and downstream monitoring of contaminants (at trace levels) is desirable to evaluate and optimize performance. -
Greater initial cost compared to gas-phase filtration and accumulation of maintenance expenses over time. -
Installation of permanent in-duct systems requires optimization of up to eight process variables (ion level, power capacity, airflow area, airflow, humidity, outside and return air quality, and ozone production. Both Mr. Zitin and Dr. Daniels acknowledge the fact that ozone is produced and that its control is a consideration in the safe and effective operation of bi-polar ionization systems.
There have been no peer-reviewed scientific studies documenting the effectiveness of bio-polar ionization for the control of gaseous contaminants. The claim of a 20-40% single pass removal efficiency for some contaminant cannot be substantiated as it can for traditional sorbent-based air cleaners by measuring contaminant concentrations upstream and downstream of the gas-phase filter (system). Manufacturers of bi-polar ionization systems confirm this and say that the effects have to be measured in the treated space(s). This is only one instance where the problems with this technology for controlling gaseous contaminants begin to surface.
The Bottom Line – Purafil Gas-Phase Air Filtration vs. Bi-polar Ionization
Purafil’s gas-phase air filtration media and systems are designed in such a way as to optimize the safe and effective removal of general and specific air contaminants. This is accomplished by the processes of adsorption, absorption, and/or chemisorption, but it is chemisorption that would be most comparable to how bi-polar ionizations systems claim to work against gas-phase contaminants.
Chemisorption involves the use of specific chemical impregnants (or additives) that can target specific contaminants or whole groups of contaminants. Contaminants can be removed by (acid-base) neutralization reactions, reduction, or oxidation. Which reaction mechanism is employed depends on the chemical characteristics of the contaminant(s).
Purafil’s gas-phase air filtration systems are proven effective at removing a myriad of chemical contaminants from the air and do not produce or release unwanted and potentially hazardous chemicals or reaction by-products into the air. Until and unless the manufacturers of bi-polar ionization systems can prove that the normal operation of these systems do not produce harmful materials such as ozone and nitrogen dioxide, do not emit dangerous reaction by-products into the air, and performance can be verified and quantified by standardized testing, we have to assume that their claims for the control of gas-phase contamination are greatly overstated at best and downright fabrications at worst. When it comes to the control of chemical contaminants from the air, stay with the company that has been and is “First …in clean air. | BI-POLAR IONIZATION CLAIMS | PURAFIL’S REBUTTAL | | By separation and oxidation, bipolar ionization will reduce many chemical gases to simpler and less obnoxious form. | In addition to the direct effects on people from ozone exposure, for many of the chemicals with which ozone does readily react, the reactions can form a variety of harmful or irritating by-products that are released into the air. With Purafil’s sorbent-based air gas-phase air filtration system, reaction by-products – with the exception of carbon dioxide and water – are bound irreversibly to the media and cannot be released back into the airstream. | | “Will not produce ozone in concentrations exceeding 0.015 ppm.” (15 ppb) | Dr. Richard Corsi of the University of Texas at Austin, a noted expert on indoor air quality and indoor air chemistry states that “All ionic air purifiers produce ozone as a by-product.” He has also looked at the effects of ozone in indoor environments. There are studies that raise serious concerns about the safety of adding ozone to indoor air – whether intentionally or unintentionally. Small increases in ozone have been shown to have significant effects on mortality, asthma symptoms and respiratory discomfort. For example, Dr. Michelle Bell of Yale University found in her study published in the Journal of the American Medical Association (JAMA) in 2004 that just a 10 ppb increase in environmental ozone caused a 0.52% increase in mortality or about 4,000 deaths per year. In another study published in Environmental Health Perspectives, Bell, et al. found that there were significant health effects for ANY increase in ozone - even less than 10 ppb. Gent, et al. also in a JAMA article in 2003 found that increases in ozone of 50 ppb were detrimental to children with asthma. These increases resulted in a 35% increase in likelihood of wheezing and a 47% increase in chest tightness. Triche, et al. in an article in Environmental Health Perspectives in 2006 found that infants (especially those with asthmatic mothers) had significant increases in wheezing and breathing difficulties with small increases in ozone at or below EPA standards. | | The bi-polar system produces an electromagnetic field (plasma) in the vicinity of the ionization tube that can dissociate different types of gaseous compounds. Free radicals are formed when electrons are stripped from the chemical molecule. In the presence of polarized air an oxidation process takes place which then changes the chemical to a simpler and less complex form. | Oxygen free radicals or reactive oxygen species (ROS) are implicated in many diseases including neurodegenerative diseases (ALS, Parkinson's, Alzheimer's), cataractogenesis, atherosclerosis, diabetes mellitus, ischemia-reperfusion injury, kwashiorkor, certain toxicities, to mention only a few, as well as in the aging process itself. Practically every type of molecule: DNA, protein, lipid, carbohydrate, can be a target and thus be damaged by a “hit”from a highly reactive radical. Normally, the body can handle free radicals, but if the free-radical production becomes excessive, damage can occur. | | If the electric field is strong enough to start the process of dissociation, a complete breakdown will occur; therefore, other harmful compounds will not be generated. | Dissociation is defined as breaking down of a compound into its components which can be simpler groups of atoms, single atoms, or ions. By “complete breakdown” most manufacturers of bi-polar ionization systems show how hydrocarbons are broken down into carbon dioxide and water. They ignore the fact that chemical intermediaries can be formed – especially from large complex molecules – that can be more dangerous than the original compounds. Also, organic nitrogen and sulfur compounds along with inorganic molecules are almost universally ignored. | | Bi-polar ionization has been found to be effective on hydrogen sulfide, ammonia, formaldehyde and similar compounds. | Oxidation of hydrogen sulfide (H2S) and ammonia (NH3) would produce sulfur dioxide (SO2) and nitrogen dioxide (NO2), respectively, which could further oxidize to sulfuric acid (H2SO4) and nitric acid (HNO3). Purafil’s dry-scrubbing media reacts with these compounds to form non-toxic salts that remain irreversibly bound to the media and will not be released back into the air. | | “Typical single pass efficiencies are 20% to 40% depending on the chemicals.” | One cannot directly measure the effects of these systems as you would traditional gas-phase air cleaning devices, i.e. up and downstream of the gas-phase air filters. Further, there is no design guidance as to contact efficiencies, residence times, etc., necessary to achieve these results. The manufacturers claim the effects can only be demonstrated in the ductwork or in the treated space(s). | | System selection for gas-phase contaminant control should include bi-polar ionization as the primary control method and gas-phase (or dry-scrubbing) air filtration as the secondary control method. The secondary control method is normally used to enhance performance of primary method and is required for many applications. | Most manufacturers do not recommend bi-polar ionization as a standalone control strategy for gaseous contaminants. This is either documented in their application / design guides or begrudgingly admitted to when pressed as to specifics of system performance. | | The effectiveness of bi-polar ionizations against different types of chemical contaminants is listed as “Excellent,” “Good,” “Fair,” or “Poor” with associated “Performance Factors.” | No quantification of performance is given (e.g. removal capacities) for any chemical contaminant nor is there any explanation of performance factors or how they were derived. Purafil publishes the choice of media and removal capacities for over 400 different chemicals. Capacities are determined following ASTM Standard Test Methods or other standardized protocols and independent verification of performance are available. | | In a letter from the U.S. Department of Agriculture: “As this equipment …is non-ozone producing, paragraph 7:16 (a) and (b) of the inspection manual do not apply to this equipment. Air sterilizer model “Bioklimatik.” | This directly contradicts manufacturers’ statements that ozone is a by-product of any ionization process or high voltage field. | | “Forms CO2 and H2O through an oxidation process. Limited numbers of chemicals are controlled.” “Gas phase chemicals are oxidized to H2O and CO2.” “Odorous gases and aerosols oxidize on contact with active oxygen molecules.” “Standard ionisers can be efficient for VOC abatement in ambient air on condition that their concentrations are lower than 10 ppm and their structure is not complex (< 6-7 carbon atoms). The efficiency decreases when the relative humidity increases. No intermediate VOCs have been identified as product of incomplete ionization due to their very unstable structures.” | Although some bi-polar ionization manufacturers’ literature are conservative in their claims for the chemicals that can be controlled, most lists hundreds of individual chemicals and chemical types that can be controlled – one manufacturer provides four pages of a “Selection Guide, Chemical Contaminants”. They also list many general applications, e.g. airports, chemical laboratory, fish market, photo laboratory, tobacco smoke, and more that would require the control of dozens, if not hundreds, of individual chemicals – many inorganic – that would not simply be oxidized to CO2 and water. Although ozone has been shown to remove some odors through an oxidation reaction, it is not effective on all odorous molecules. In some cases, more noxious or potentially toxic by-products such as nitrogen dioxide and sulfur trioxide may be formed. | | Ozone is a by-product of any ionization process or high voltage field. When operated in accordance with manufacturer’s instructions, non-detectable concentrations of ozone will result. | It depends on one’s definition of “non-detectable” as to whether 15 ppb of ozone meets this criterion. Further, the corona discharge that creates the ozone also produces nitrogen oxides which are more of an irritant than ozone. According to Dr. Charles Weschler, an expert in indoor air chemistry and an Adjunct Professor in the UMDNJ-RWJMS Department of Environmental and Occupational Medicine and a visiting professor at the International Centre for Indoor Environment and Energy, Technical University of Denmark, ozone catalyzes the conversion of NO to NO2 and NO2 to nitric acid (HNO3). | | “Odors, especially of an organic origin, are quickly eliminated.” “The ionization cannot be seen, but its presence will result in a “mountain air” freshness.” | Some have insisted that even if ozone does not paralyze the olfactory sense, its odor is such that it “masks” other odors rather than actually removing or neutralizing them. | | The use of bi-polar ionization complies with the requirements of the Indoor Air Quality Procedure of ASHRAE Standard 62. | The use of the IAQ Procedure require documentation as to the effectiveness of the air cleaning system towards the contaminants of concern identified in the HVAC system design criteria. There has been no independent testing performed to prove the effectiveness of bi-polar ionization. Most of what information is publicly available is either produced by the manufacturer or is of an anecdotal nature. Purafil can provide independent test reports for all of our media and filter products. | Final Thoughts
Any air cleaning system being used to control gaseous contaminants must be able to document its performance in accordance to some type of standardized testing. Statements such as “You cannot measure the effectiveness of this system by monitoring upstream and downstream of the unit. You must measure the effects in the treated space” are intended for the uninformed and those looking for a $1.00 solution to a $10.00 problem. Many of these systems are relatively inexpensive, require little maintenance, and have low installation and operating costs. This makes it attractive to the purchasing agent, but does not solve the air quality problems – in fact these systems can actually add to the problem through their “unintentional consequences” of uncontrolled ozone production and the formation of harmful (oxidation) reaction by-products. If you want smoke and mirrors, go with bi-polar ionization. If you want something that works, stay with the company that has been doing this for more than 40 years – Purafil. Related Links / Events: |
