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. Intuitively, the logic is compelling. Unfortunately, there is no simple solution as google throws up an avalanche of controversy within seconds. 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 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. 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. A dominant current trend appears to be the creation of an invisible but potent defence shield against airborne molecular contaminants. 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. Conversely, in active mode, reactive agents are pumped into the impure air environment. 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. Known as nature's detergent, hydroxyl is a powerful reactive species that plucks out hydrogen molecules from the organic structure of these airborne particulates, thereby killing them. Harmless by-products, mainly water, are generated by this chemical reaction.
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. Adherents of the negative ions technology expound the view that negative ions dominate these natural habitats and 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 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. 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.
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. Large numbers of negative ions are produced as water droplets are split. 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. Millions of negatively-charged electrons are produced when a high voltage pulse is applied to the electrode. This method does not result in ozone being produced. 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. Between the two electrodes, a high voltage is applied. This causes the movement of electrons between the electrodes thereby ionising the air in between them. 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 (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 odours and chemicals - toluene, chloroform, hexane, ethanol, formaldehyde, ethylene etc, 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.
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.
Impure air is sucked into the electrostatic purifier and passed over the dielectric material which acts like a sieve. Electrostatic electricity between the electrodes causes airborne particulates i.e.smoke contaminants, dust, etc, to adhere to the dielectric surface. From the other end of the purifier, purified air emerges.
Frequently, an ion source is planted just before the electrostatic filter to electrically charge the airborne particulates. These impurities, so charged, 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 greater depth 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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