Ionic Air Purifier Technologies - Scientific Fact or Science Fiction?
Introduction
Ionic air purifiers hold the promise of clean air, purified of all known harmful contaminants that threaten our health. Our naked eyes cannot see these harmful impurities. Invisible weapons against invisible enemies seems the obvious answer. Intuitively, the logic appeals to me. Sadly, google has no quick answer to meet my simple expectation. Instead, controversy abounds. It is quite clear that the urge to rush out and buy an ionic air purifier must be suppressed at the moment. The search for an ionic air purifier must focus on its safety aspects as much, if not more, than its effectiveness against contaminants.
The recent China melamine saga that killed infants also serves as a reminder to us that in buying into any technology or any product, all claims by manufacturers and distributors must be screened to the fullest extent that our resources permit. Where the reactive agent is invisible, it becomes even more critical to focus on it. My investigation of ionic air purifier technologies falls within this realm, as the reactive agents are ions that are invisible to our eyes.
In this article, I am laying out the roadmap as I look into the existing ionic air purifier technologies in the global marketplace. My back-to-basics approach is an attempt, as a layperson, to understand the science behind the technology. The creation of a powerful invisible defence shield against airborne molecular contaminants is increasingly taking centrestage. The dominant global health threat under the scrutiny of scientists is the avian flu virus.
Types of Ionic Air Purifier Technologies
Broadly speaking, air purification technologies can be deployed in either passive or active modes. Under passive technology modes, reactive agents are contained in the air purifier whilst impure air is drawn in for cleansing before being pushed back to the environment. Active mode depicts the proactive process of bringing the purifying reactive agents into the surrounding impure air. Interestingly, marketeers betray their lack of confidence in their own ionic air purifier technologies by combining both passive and active modes.
In the global market today, ionic air purifier technologies include the following categories:
(A) Ion generator - positive and negative ions
(B) Ion generator - negative ions only
(C) Photocatalytic Oxidation (POC)
(D) Electrostatic filter
(E) Combos
Ion Generator - Positive and Negative Ions
This combination of positive and negative ions appears to show the most promise for the future of ionic air purifier technology. Developed by Japanese ingenuity, Sharp Corporation to be exact, they are known as plasmacluster ions.
Positive and negative plasmacluster ions actively surround harmful bacteria and viruses in a deadly embrace. In so doing, the production of hydroxyl is activated. Known as nature’s detergent, hydroxyl is a powerful reactive species that plucks out hydrogen molecules from the organic structure of these airborne particulates, thereby killing them. Harmless by-products, mainly water, are generated by this chemical reaction.
A differential ion generator is used in this technology, comprising a positive and a negative ion generator which can be powered in alternate cycles to control the type of ions generated.
Advocates of the positive and negative ions combination claim that a balance of both these ion types is to be found in places like waterfalls and pristine forests, i.e. this is the actual state in nature. Diametrically, believers of the negative ions technology take the view that negative ions dominate the space in natural habitats and that positive ions are actually harmful. In this regard, I have yet to find independent scientific studies as evidence for the contradictory claims of both camps.
Ion Generator - Negative Ions
The traditional ionic air purifier produces only negative ions. Currently, this technology dominates market share but it is under serious threat from Sharp’s plasmacluster positive and negative ions technology.
It is claimed that nearly all harmful airborne particulates like dust, smoke and bacteria etc have a positive charge. Negative ions from the air purifier attach themselves to these particulates until they get weighed down and fall to the ground. Thereafter, simple vacuuming removes these impurities. Critics of negative ion technology charge that the weighed down particulates are not destroyed and the mere act of walking around the room kicks them back into the air that we breathe.
In addition, there appears to be several methods of producing the negative ions. It is critical to know the various methods as each may have different by-products, some harmful and some which are not. These methods include:
(1) Water method - this employs what is known as the waterfall or Lenard Effect. Water droplets are splashed onto a metal plate where a small electric charge is applied. The charge splits the water droplets resulting in the production of a large number of negative ions. No harmful by-products result from using the water method to produce ions.
(2) Electron radiation method - this is based on a single negative discharge electrode needle. Negatively-charged electrons are produced by the millions when a high voltage pulse is applied to the electrode. This method does not result in ozone being generated. It is claimed that this is because a “smaller” energy pulse is applied.
(3) Corona discharge method - this is based on a dual electrode model, a sharp metal electrode and a flat electrode. High voltage is applied between the electrodes. This creates a massive movement of electrons between the electrodes and ionises the air in between them. This method has been criticised for the production of harmful by-products like ozone and nitride oxide.
Photocatalytic Oxidation (POC)
This technology is commonly applied in a passive mode. Hydroxyl, nature’s detergent, is the key reactive agent in POC technology.
Germicidal ultraviolet (UV) light is commonly shone on a catalyst (usually titanium oxide) to produce hydroxyl, oxygen and peroxide, all of which are potent oxidising agents that are very effective at destroying the organic structure of micro-organisms and gaseous volatile organic compounds.
The key pillar of POC technology is its comprehensive coverage. Proponents of this technology claim that POC inactivates ALL categories of indoor pollution, including:
(1) airborne particulates i.e. dust, pet dander, plant pollen, sea salts, tobacco smoke, industrial and car pollution, etc
(2) bioaerosols i.e. infectious biological compounds (e.g. pathogenic bacteria and viruses) or non-infectious and non-contagious (e.g. non-pathogenic bacteria, molds, cell debris)
(3) volatile organic compounds (VOCs) i.e. gaseous chemicals or odours - benzene, toluene, chloroform, ethanol, formaldehyde, etc, all common emissions from everyday products of our modern home.
Detractors of POC technology are wary of the inability of hydroxyl to distinguish between the organic structures of molecular contaminants and that of our nose membrane, lung tissue and eye cornea.
Electrostatic Filter
This technology appears to have originated in heavy industries which produced abundant pollutants. The typical electrostatic filter ionic air purifier includes two electrodes sandwiching a porous dielectric material. A dielectric material does not conduct electricity while metallic electrodes are good conductors that transmit or receive electricity.
Impure air is sucked into the electrostatic purifier and passed over the dielectric material which acts like a sieve. The electrostatic field between the electrodes causes airborne particulates i.e.smoke contaminants, dust, etc, to stick to the dielectric surface. Purified air emerges from the other end of the purifier.
Very often, an ion source is inserted before the electrostatic filter to charge the airborne particulates. These impurities, so charged, stick more effectively to the dielectric material.
The general criticism of ionisation technology applies to electrostatic filters as well i.e. that harmful ozone is a by-product.
Combo Ionic Air Purifiers
To cater to the various adherents and critics of the diverse technologies, combos incorporate all or some of the above types of technologies. Combos may include:
(1) adsorptive materials such as activated carbon or oxygenated charcoal (known for its extremely porous large surface area) are added to POC technology to enhance the removal of VOCs;
(2) oxidizing catalysts like titanium oxide are coated on various components of all types of air purifiers to enhance VOC elimination;
(3) reducing catalysts such as manganese dioxide are coated near the exit outlets of many air purifiers to reduce reactive species like ozone and nitric oxide which may be harmful;
(4) generating ions by differing methods such as using microwave, UV light, radio frequency waves, and direct current;
(5) tweaking the specifications of any ionic air purifier technology so as to attain the well-known HEPA status without actually using HEPA filters.
Obviously, the process of selecting the most efficient and effective ionic air purifier involves analysing a deluge of information. And I have not even touched on the safety aspects of each technology. Nor have I studied in detail the claims of each technology. It is natural to want to quickly want something that promises to improve the air quality in your homes, offices, factories, schools etc. But I urge you to do your homework and don’t forget to visit me for updates as I continue my search for the ideal ionic air purifier.
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