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. The intuitive logic draws me. Sadly, google has no quick answer to meet my simple expectation. Instead, controversy abounds. It is quite clear that the urge to rush out and buy an ionic air purifier must be suppressed at the moment. Safety, more than effectiveness, must be given higher weightage in the selection of 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 technologies in the global marketplace. As laypersons, I believe we have to adopt a back-to-basics approach to try and understand the technologies. 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. 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 Corporation's marketing efforts focus on the ability of plasmacluster ions to surround and cling on to harmful airborne bacteria and viruses. When clumping occurs, 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. This chemical reaction generates harmless by-products, the main of which is water.
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. 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. 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. Negatively charged ions are naturally attracted to these particulates until they sink to the ground by sheer weight. Vacuuming removes these neutralised impurities and therefore protects us from them. 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. 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 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. Negatively-charged electrons are produced by the millions when a high voltage pulse is applied to the electrode. This process does not generate any ozone. 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. An extremely high voltage is then applied to the two electrodes. This creates a massive movement of electrons between the electrodes and ionises 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. The key reactive purifying agent is hydroxyl, nature's detergent.
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, toluene, chloroform, ethanol, formaldehyde, 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. Typically, an electrostatic filter is made of a porous dielectric material that is positioned between two electrodes. Dielectric materials do not conduct electricity while metallic electrodes are excellent conductors that transmit and receive electricity.
Impure air is sucked into the electrostatic purifier and passed over the dielectric material which acts like a sieve. Electrostatic forces between the electrodes causes airborne particulates i.e.smoke contaminants, dust, etc, to stick to the dielectric surface. Purified air emerges from the other end of the purifier.
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.
The general criticism of ionisation technology applies to electrostatic filters as well i.e. that harmful ozone is a by-product.
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. I have barely skimmed the surface of the safety issues 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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