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. Invisible weapons against invisible enemies seems the obvious answer. I find the intuitive logic appealing. Sadly, google has no quick answer to meet my simple expectation. Instead, controversy abounds. 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. Product safety must take precedence over effectiveness in choosing 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 technology in the 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 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. 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. 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. In so doing, the production of hydroxyl is activated. 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. The by-products of this chemical reaction, mainly water, are harmless.

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. In contrast, proponents of negative ions technology insist that negative ions fill natural habitats and that the presence of positive ions is 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. 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. 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. Water droplets are splashed onto a metal plate where a small electric charge is applied. This simple action results in the splitting of water droplets, causing the production of large numbers 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. 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. High voltage is applied between the electrodes. This creates a massive movement of electrons between the electrodes and ionises 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. pathogenic bacteria and viruses) or non-contagious and 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, 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. The typical arrangement in an electrostatic filter ionic air purifier comprises a porous dielectric material sandwiched between two electrodes. A dielectric material does not conduct electricity while metallic electrodes are good conductors that transmit or receive electricity.

Contaminated air is drawn into the electrostatic puriifer and made to pass over the dielectric material which acts like a sieve. 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.

Frequently, an ion source is planted just before the electrostatic filter to electrically 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. I will also be studying in detail 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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