Introduction
Ionic air purifiers hold the promise of clean air, purified of all known harmful contaminants that threaten our health. The harmful impurities in the air are not visible to our naked eye. Invisible ions battling invisible contaminants appears to make perfect sense. I am drawn to this intuitive logic. But these days, finding a simple and quick solution is rare. Googling the subject unearths a ton of controversy. It is quite clear that the urge to rush out and buy an ionic air purifier must be suppressed at the moment. Safety, more than effectiveness, must be given higher weightage in the selection of an ionic air purifier.
The recent China melamine saga that killed infants also is a timely 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. This is especially so where the key reactive agent is invisible to the naked eye. Invisible ions produced by ionic air purifiers are clearly in this category.
This article is an overview of existing ionic air purifier technologies in the global marketplace. As laypersons, I believe we have to adopt a back-to-basics approach to try and understand the technologies. A dominant current trend appears to be the creation of an invisible but potent defence shield against airborne molecular contaminants. The prime threat being closely monitored by scientists all over the world 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. Combinations of both passive and active modes are often found in many types of ionic air purifiers.
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. They have been named as plasmacluster ions by Sharp Corporation, the Japanese corporate powerhouse that invented them.
Sharp Corporation's marketing efforts focus on the ability of plasmacluster ions to surround and cling on to harmful airborne bacteria and viruses. 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 real state of the natural environment. 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. As I progress with my research, I shall be looking for independent scientific studies that support either of these two opposing views.
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. The positive charges are continually attracted to the negative charges of the ions until sheer mass makes them sink to the ground. These impurities are simply removed by vacuuming. Weighing down the particulates does nothing to destory them, according to critics, and merely walking on them causes the air to be polluted again.
Apparently, there are a number of ways to produce negative ions. This has significance as the various methods result in different by-products, some of which are harmful. 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. The simple application of a high voltage pulse to the electrode results in millions of negatively-charged electrons being produced. An advantage of this method is that no ozone is produced. This is due to the application of a "smaller" energy pulse.
(3) Corona discharge method - this is based on a dual electrode model, a sharp metal electrode and a flat electrode. Between the two electrodes, a high voltage is applied. The movement of electrons between the electrodes ionises the air in that same space. An inherent flaw of this method is the production of harmful by-products like ozone and nitride oxide.
Photocatalytic Oxidation (POC)
This technology is commonly applied in a passive mode. In POC, the powerful reactive agent hydroxyl is also the key to the purifying process.
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.
Comprehensive defence is the key strength of POC technology. 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. contagious or infectious biological compounds (e.g. viruses and pathogenic bacteria) or non-infectious (e.g. non-pathogenic bacteria, molds, cell debris)
(3) volatile organic compounds (VOCs) i.e. gaseous chemicals or odours - benzene, styrene, toluene, chloroform, hexane, ethanol, formaldehyde and ethylene all common emissions from everyday products of our modern home.
Critics of POC zoom in on the power effects of hydroxyl, claiming that they cannot differentiate between the organic structures that make up molecular contaminants and our lung tissue, eye cornea or nose membranes.
Electrostatic Filter
This technology appears to have originated in heavy industries which produced abundant pollutants. The typical arrangement in an electrostatic filter ionic air purifier comprises a porous dielectric material sandwiched between two electrodes. Dielectric materials do not conduct electricity while metallic electrodes are excellent conductors that transmit and receive electricity.
As impure air is drawn into the electrostatic purifier, it passes through the dielectric material which acts as a sieve. The electrostatic field created between the electrodes causes airborne particulates i.e.dust, smoke contaminants, etc, to adhere to the surface of the dielectric. From the other end of the purifier, purified air emerges.
Frequently, an ion source is planted just before the electrostatic filter to electrically charge the airborne particulates. The impurities, now carrying an electrical charge, stick more effectively to the dielectric material.
Critics of this technology point to the production of harmful ozone in the ionisation process.
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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