Ionic Air Purifier Technologies - Will Someone Tell Us The Truth?
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 ions battling invisible contaminants appears to make perfect sense. I find the intuitive logic appealing. Yet, even before an hour of internet research has lapsed, a whole deluge of controversy is thrown up by google. It is quite clear that the urge to rush out and buy an ionic air purifier must be suppressed at the moment. Effectiveness is important but safety is paramount in the criteria for selecting 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. Where the reactive agent is invisible, it becomes even more critical to focus on it. 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 technologies in the global marketplace. My back-to-basics approach is an attempt, as a layperson, to understand the science behind the technology. The creation of a powerful invisible defence shield against airborne molecular contaminants is increasingly taking centrestage. 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. 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. It is not unusual to find combinations of both passive and active modes in many ionic air puriifers.
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. They have been named as plasmacluster ions by Sharp Corporation, the Japanese corporate powerhouse that invented them.
Positive and negative plasmacluster ions actively surround harmful bacteria and viruses in a deadly embrace. When this happens, 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. Harmless by-products, mainly water, are generated by this chemical reaction.
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. 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. Apparently, negative ions technology dominates the ionic air purifier market at the moment but Sharp’s plamascluster technology is increasingly proving to be a serious alternative.
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. Detractors of negative ion technology believe that the “overweight” particulates on the ground are not destroyed and that the mere act of walking on them re-contaminates the air.
There appears to be several methods of producing negative ions. It is critical to know the various methods as each may have different by-products, some harmful and some which are not. 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 simple action results in the splitting of water droplets, causing the production of large numbers of negative ions. 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. Applying a high voltage pulse to the electrode results in the production of millions of negatively-charged electrons. An advantage of this method is that no ozone is produced. It is claimed that this is because a “smaller” energy pulse is 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. This causes the movement of electrons between the electrodes thereby ionising the air in between them. An inherent flaw 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 relies on the production of the powerful reactive agent, hydroxyl.
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. 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.
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. 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, etc, to adhere to the surface of the dielectric. Out of the other end of the purifier, cleaned air is recirculated.
An ion source is often placed before the electrostatic filter to impart an electric charge to 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 have also not examined in greater depth 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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