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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. Invisible ions battling invisible contaminants appears to make perfect sense. Intuitively, the logic appeals to me. But these days, finding a simple and quick solution is rare. Googling the subject unearths a ton of controversy. Obviously, I must resist the urge to go by intuition and grab the first ionic air purifier that I lay hands on. 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 is a timely 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. My investigation of ionic air purifier technologies falls within this realm, as the reactive agents are ions that are invisible to our eyes.

In this article, I am laying out the roadmap as I look into the 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 current key trend appears to be the creation of a potent invisible defence shield against airborne molecular contaminants that threaten our well-being. The predominant airborne threat being monitored by scientists the world over 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. In active mode, the reactive agents are pushed into the environment with the impure air. 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. Developed by Japanese ingenuity, Sharp Corporation to be exact, they are known as plasmacluster ions.

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. 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 real state of the natural environment. Diametrically, believers of the negative ions technology take the view that negative ions dominate the space in natural habitats and that positive ions are actually 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 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. 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.

Apparently, there are a number of ways to produce 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. Water droplets are splashed onto a metal plate where a small electric charge is applied. The charge splits the water droplets resulting in the production of a large number of negative ions. Proponents of the water method believe it to be free of harmful by-products.

(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. An extremely high voltage is then applied to the two electrodes. This causes the movement of electrons between the electrodes thereby ionising the air in between them. 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. 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.

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. contagious or infectious biological compounds (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.

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. The dielectric material impedes electrical conductivity whilst the electrodes efficiently conduct electricity.

Impure air is drawn into the electrostatic purifier so that it passes over the dielectric material. The electrostatic field between the electrodes causes airborne particulates i.e.smoke contaminants, dust, etc, to adhere to the dielectric surface. Purified air emerges from the other end of the purifier.

Very often, an ion source is inserted before the electrostatic filter to charge the airborne particulates. These impurities, so charged, stick more effectively to the dielectric material.

Criticism of electrostatic filter technology focuses on ozone as a by-product, commonly assumed to be produced in all ionisation processes.

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 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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