Introduction
Ionic air purifiers hold the promise of clean air, purified of all known harmful contaminants that threaten our health. Air is made impure by substances unseen by our naked eye. Invisible weapons against invisible enemies seems the obvious answer. I am drawn to this intuitive logic. 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 examined to the fullest extent that our resources permit. This is especially so where the key reactive agent is invisible to the naked eye. Investigating ionic air purifier technologies falls within this ambit as the reactive agents are invisible ions.
In this space, I am providing an overview of the existing ionic air purifier technology in the global market. Trying to understand the science behind the technologies seems to be the logical place to begin searching for the ideal ionic air purifier. The current key trend appears to be the creation of a potent invisible defence shield against airborne molecular contaminants that threaten our well-being. 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. Passive mode technologies incorporate means by which impure air is sucked into the air purifier for reactive agents to work on before being re-introduced into the environment as cleaned air. 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. Pioneered by the Japanese corporate giant, Sharp Corporation, they are known as plasmacluster ions.
Sharp explains that the plasmacluster of positive and negative ions clump to harmful airborne bacteria and viruses. When clumping occurs, hydroxyl is produced. Commonly known as nature’s detergent, hydroxyl is a powerful reactive species that destroys airborne particulates by removing hydrogen molecules from their organic structures. This chemical reaction generates harmless by-products, the main of which is water.
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. In contrast, proponents of negative ions technology insist that negative ions fill natural habitats and that the presence of positive ions is 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. The positive charges are continually attracted to the negative charges of the ions until sheer mass makes them sink to the ground. Regular vacuuming removes these impurities from our environment. 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. 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. Onto an electrically-charged metal plate, water droplets are splashed. This splits the water droplets, a process in which large numbers of negative ions are produced. 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. This method does not result in ozone being generated. 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. A very high voltage is applied between the two electrodes. The movement of electrons between the electrodes ionises the air in that same space. 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.
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. viruses and pathogenic bacteria) 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, styrene, toluene, chloroform, hexane, ethanol, formaldehyde and ethylene 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. Typically, an electrostatic filter is made of a porous dielectric material that is positioned between two electrodes. The dielectric material impedes electrical conductivity whilst the electrodes efficiently conduct electricity.
Contaminated air is drawn into the electrostatic puriifer and made to pass over the dielectric material which acts like a sieve. Electrostatic electricity between the electrodes causes airborne particulates i.e.dust, smoke contaminants, to stick to the surface of the dielectric. Purified air is pushed out of the purifier and re-circulated.
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. The safety issues of each technology will need much more investigation. I will also be studying in detail the claims of each technology. I urge you not to rush out to get the latest air purifier for your homes, offices, factories, schools etc. Do your homework and check back here for updates as I continue to find the ideal ionic air purifier.
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