Introduction

Ionic air purifiers hold the promise of clean air, purified of all known harmful contaminants that threaten our health. These harmful contaminants are not visible to our naked eyes. The weapons against such are very likely to be invisible to our eyes as well. I am drawn to this intuitive logic. 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. 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. Invisible ions produced by ionic air purifiers are clearly in this category.

This article is an overview of existing ionic air purifier technology in the marketplace. As laypersons, I believe we have to adopt a back-to-basics approach to try and understand the technologies. 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 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 mode technologies incorporate means by which impure air is sucked into the air purifier for reactive agents to work on before being re-introduced into the environment as cleaned air. Active mode depicts the proactive process of bringing the purifying reactive agents into the surrounding 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. They have been named as plasmacluster ions by Sharp Corporation, the Japanese corporate powerhouse that invented them.

Sharp explains that the plasmacluster of positive and negative ions clump to harmful airborne bacteria and viruses. In so doing, the production of hydroxyl is activated. 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. 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. 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. 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. Vacuuming removes these neutralised impurities and therefore protects us from them. Weighing down the particulates does nothing to destory them, according to critics, and merely walking on them causes the air to be polluted again.

It seems that there are several 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. Large numbers of negative ions are produced as water droplets are split. 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. The simple application of a high voltage pulse to the electrode results in millions of negatively-charged electrons being produced. It is claimed that this method produces no ozone. 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. Between the two electrodes, a high voltage is applied. 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.

The key pillar of POC technology is its comprehensive coverage. 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 (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.

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. 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 drawn into the electrostatic purifier so that it passes over the dielectric material. The electrostatic field created 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.

Very often, an ion source is inserted before the electrostatic filter to charge 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. I have barely skimmed the surface of the safety issues of each technology. Nor have I studied 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 check back here for updates as I continue to look for the ideal ionic air purifier.

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