Ionic Air Purifier Technologies – Friend or Foe?
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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. Yet, even before an hour of internet research has lapsed, a whole deluge of controversy is thrown up by google. 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 even more critical when the key reactive agent is unseen to the human eye. My investigation of ionic air purifier technologies falls within this realm, as the reactive agents are ions that are invisible to our eyes.
This article is an overview of existing ionic air purifier technology in the marketplace. My back-to-basics approach is an attempt, as a layperson, to understand the science behind the technology. 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 typically means that impure air is drawn into the air purifier for the 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. 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. 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. 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 particles, thereby killing 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 real state of the natural environment. 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 method seems to dominate market share in the industry but is coming 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. Negative ions from the air purifier attach themselves to these particulates until they get weighed down and fall to the ground. Vacuuming removes these neutralised impurities and therefore protects us from them. 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 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. 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. Millions of negatively-charged electrons are produced when a high voltage pulse is applied to the electrode. 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. High voltage is applied between the electrodes. The movement of electrons between the electrodes ionises the air in that same space. A criticism 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. 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 (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.
An academic commentary by an US university seems to suggest that POC technology is more effective against VOCs in the parts-per-million concentration range and may not be applicable to concentrations in the parts-per-billion range that is more typical of indoor air quality environments.
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.
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, to stick to the surface of the dielectric. From the other end of the purifier, purified air emerges.
An ion source is often 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.
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. 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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