Introduction
Ionic air purifiers hold the promise of clean air, purified of all known harmful contaminants that threaten our health. Naked eyes cannot see these harmful contaminants. The weapons against such are very likely to be invisible to our eyes as well. Intuitively, the logic is appealing. Unfortunately, there is no simple solution as google throws up an avalanche of controversy within seconds. Obviously, I must resist the urge to go by intuition and grab the first ionic air purifier that I lay hands on. 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. 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 technology in the marketplace. As laypersons, I believe we have to adopt a back-to-basics approach to try and understand the technologies. The creation of a powerful invisible defence shield against airborne molecular contaminants is increasingly taking centrestage. 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 generally means dispersive processes by which the impure air is penetrated and purified by the reactive agents. 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. They have been named as plasmacluster ions by Sharp Corporation, the Japanese corporate powerhouse that invented them.
Sharp explains that the plasmacluster of positive and negative ions clump to harmful airborne bacteria and viruses. In so doing, the production of hydroxyl is activated. Commonly known as nature’s detergent, hydroxyl is a powerful reactive species that destroys airborne particulates by removing hydrogen molecules from their organic structures. The by-products of this chemical reaction, mainly water, are harmless.
This technology uses a differential ion generator, 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. Proponents of negative ions believe that negative ions dominate the environment in these natural habitats and even insist that positive ions are harmful. Thus far, I have not found any independent scientific studies to support the opposing claims of the two technologies.
Ion Generator - Negative Ions
The traditional ionic air purifier produces only negative ions. This technology appears to have the main market share currently but is facing a serious challenge 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. Negatively charged ions are naturally attracted to these particulates until they sink to the ground by sheer weight. These impurities are simply removed by vacuuming. 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.
It seems that there are several ways to produce negative ions. It is crucial to know the various methods as each may have 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. Onto a metal plate that is electrically-charged, water droplets are splashed. Large numbers of negative ions are produced as water droplets are split. Proponents of the water method believe it to be free of harmful by-products.
(2) Electron radiation method - this is based on a single negative discharge electrode needle. Applying a high voltage pulse to the electrode results in the production of millions of negatively-charged electrons. This process does not generate any ozone. 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. A very high voltage is applied between the two electrodes. This creates a massive movement of electrons between the electrodes and ionises the air in between them. 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. 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.
Complete and comprehensive action is the pillar 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. 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 odours and chemicals - toluene, chloroform, hexane, ethanol, formaldehyde, ethylene etc, all common emissions from everyday products of our modern home.
POC technology has been criticised for relying on hydroxyl which are believed to attack with equal tenacity the organic structures that make up molecular contaminants and our lung tissue, nose membranes and eye cornea.
Electrostatic Filter
This technology appears to have originated in heavy industries which produced abundant pollutants. Typically, an electrostatic filter is made of a porous dielectric material that is positioned between two electrodes. A dielectric material does not conduct electricity while metallic electrodes are good conductors that transmit or receive electricity.
Contaminated air is drawn into the electrostatic puriifer and made to pass 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. From the other end of the purifier, purified air emerges.
Very often, an ion source is inserted before the electrostatic filter to 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. The safety issues of each technology will need much more investigation. 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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