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. Invisible ions battling invisible contaminants appears to make perfect sense. I am drawn to this intuitive logic. Yet, even before an hour of internet research has lapsed, a whole deluge of controversy is thrown up by google. 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. Product safety must take precedence over effectiveness in choosing an ionic air purifier.
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.
This article is an overview of existing ionic air purifier technology in the 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 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. Savvy marketeers often seek to cover all the bases by combining both passive and active modes in many 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. Pioneered by the Japanese corporate giant, Sharp Corporation, they are known as plasmacluster ions.
Sharp Corporation’s marketing efforts focus on the ability of plasmacluster ions to surround and cling on to harmful airborne bacteria and viruses. When this happens, hydroxyl is produced. Hydroxyl, also known as nature’s detergent, is a powerful reactive species that plucks out hydrogen molecules from the organic structure of these airborne particulates thereby destroying them. The by-products of this chemical reaction, mainly water, are harmless.
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. Proponents of negative ions believe that negative ions dominate the environment in these natural habitats and even insist that positive ions are 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. 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. Vacuuming removes these neutralised impurities and therefore protects us from them. Weighing down the particulates does nothing to destory them, according to critics, and merely walking on them causes the air to be polluted again.
There appears to be several methods of producing 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 a metal plate that is electrically-charged, water droplets are splashed. This splits the water droplets, a process in which large numbers of negative ions are produced. It is claimed that no harmful by-products are produced by the water method.
(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 produced. This is believed to be 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. An extremely high voltage is then applied to the two electrodes. This causes the movement of electrons between the electrodes thereby ionising the air in between them. An inherent weakness 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. 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.
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. In the most common electrostatic filter arrangement, there is a porous dielectric material positioned 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. Electrostatic forces between the electrodes causes airborne particulates i.e.dust, smoke contaminants, etc, to stick to the dielectric surface. Out of the other end of the purifier, cleaned air is recirculated.
Quite often, an ion source is placed before the electrostatic filter to impart an electric charge to the airborne particulates. Charging the impurities make them adhere more effectively to the dielectric material.
Criticism of electrostatic filter technology focuses on ozone as a by-product, commonly assumed to be produced in all ionisation processes.
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 have also not examined in detail the claims of each technology. So before you put your money down for any air purifier in your homes, offices, schools, etc, check back here for updates as I continue my quest for the ideal ionic air purifier.
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