Introduction

Ionic air purifiers hold the promise of clean air, purified of all known harmful contaminants that threaten our health. Naked eyes cannot see these harmful contaminants. Invisible ions battling invisible contaminants appears to make perfect sense. Intuitively, the logic is appealing. Unfortunately, there is no simple solution as google throws up an avalanche of controversy within seconds. 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 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 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 technology in the 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 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. Active mode depicts the proactive process of bringing the purifying reactive agents into the surrounding 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.

Plasmaclusters of positive and negative ions encircle and latch onto harmful bacteria and viruses in a deadly grip. When clumping occurs, hydroxyl is produced. Commonly known as nature’s detergent, hydroxyl is a powerful reactive species that destroys airborne particulates by removing hydrogen molecules from their organic structures. 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. 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. 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.

There appears to be several methods of producing 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 a metal plate that is electrically-charged, water droplets are splashed. 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. 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. The movement of electrons between the electrodes ionises the air in that same space. 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. In POC, the powerful reactive agent hydroxyl is also the key to the purifying process.

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 odours and chemicals – toluene, chloroform, hexane, ethanol, formaldehyde, ethylene etc, all common emissions from everyday products of our modern home.

POC technology has been criticised for relying on hydroxyl which are believed to attack with equal tenacity the organic structures that make up molecular contaminants and our lung tissue, nose membranes and eye cornea.

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

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.

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. The safety issues of each technology will need much more investigation. Nor have I studied in detail the claims of each technology. I urge you not to rush out to get the latest air purifier for your homes, offices, factories, schools etc. Do your homework and check back here for updates as I continue to find the ideal ionic air purifier.

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