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. The weapons against such are very likely to be invisible to our eyes as well. 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. Even though I am tempted to quickly get an ionic air purifier to clean the air I breathe, it is clear that more time and effort is needed. 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 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. 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. 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. In passive mode, impure air is drawn into the air purifier for reactive agents to work on before re-emerging as cleaned air into the environment. In active mode, the reactive agents are pushed into the environment with the 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. Hydroxyl, also known as nature’s detergent, is a powerful reactive species that destroys airborne particulates by plucking out hydrogen molecules from their organic structure. 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. In contrast, proponents of negative ions technology insist that negative ions fill natural habitats and that the presence of positive ions is 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. 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.
There appears to be several methods of producing negative ions. This is important because different methods produce different by-products, some of which may be 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. This method does not result in ozone being generated. This is attributed to a “smaller” energy pulse being 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. 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. It is also based on the powerful reactive agent hydroxyl which purifies impure air that is pulled through the air purifier.
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.
It is claimed that the comprehensive defence that POC provides is its main strength. 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. biological compounds that may be infectious or contagious (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.
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. The typical arrangement in an electrostatic filter ionic air purifier comprises a porous dielectric material sandwiched 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. The electrostatic field created between the electrodes causes airborne particulates i.e.dust, smoke contaminants, etc, to stick to the dielectric surface. Purified air is pushed out of the purifier and re-circulated.
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. And I have not even touched on the safety aspects of each technology. I will also be studying 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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