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 weapons against invisible enemies seems the obvious answer. I am drawn to this intuitive logic. 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. 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 examined to the fullest extent that our resources permit. This is especially so where the key reactive agent is invisible to the naked eye. Invisible ions produced by ionic air purifiers are clearly in this category.
This article is an overview of existing ionic air purifier technologies in the global 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 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. In passive mode, impure air is drawn into the air purifier for reactive agents to work on before re-emerging as cleaned air into the environment. Active generally means dispersive processes by which the impure air is penetrated and purified by the reactive agents. 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.
Plasmaclusters of positive and negative ions encircle and latch onto harmful bacteria and viruses in a deadly grip. 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. 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. Proponents of negative ions believe that negative ions dominate the environment in these natural habitats and even insist that positive ions are harmful. As I progress with my research, I shall be looking for independent scientific studies that support either of these two opposing views.
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. Negatively charged ions are naturally attracted to these particulates until they sink to the ground by sheer weight. These impurities are simply removed by vacuuming. 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.
Apparently, there are a number of ways to produce 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. 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. The simple application of a high voltage pulse to the electrode results in millions of negatively-charged electrons being produced. 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. A very high voltage is applied between 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. 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.
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 odours and chemicals - toluene, chloroform, hexane, ethanol, formaldehyde, ethylene etc, 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. 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. Electrostatic electricity between the electrodes causes airborne particulates i.e.dust, smoke contaminants, etc, to stick to the dielectric surface. Purified air emerges from the other end of the purifier.
An ion source is often placed before the electrostatic filter to impart an electric charge to the airborne particulates. The impurities, now carrying an electrical charge, stick 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. 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. It is natural to want to quickly want something that promises to improve the air quality in your homes, offices, factories, schools etc. But I urge you to do your homework and don’t forget to visit me for updates as I continue my search for the ideal ionic air purifier.
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