Introduction

Ionic air purifiers hold the promise of clean air, purified of all known harmful contaminants that threaten our health. The harmful impurities in the air are not visible to our naked eye. Invisible weapons against invisible enemies seems the obvious answer. Intuitively, the logic appeals to me. 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. The search for an ionic air purifier must focus on its safety aspects as much, if not more, than its effectiveness against contaminants.

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. 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.

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. 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. 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. 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 this happens, hydroxyl is produced. 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. 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. 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. 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. Apparently, negative ions technology dominates the ionic air purifier market at the moment but Sharp’s plamascluster technology is increasingly proving to be a serious alternative.

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. Thereafter, simple vacuuming removes these impurities. 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.

There appears to be several methods of producing negative ions. It is crucial to know the various methods as each may have 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. No harmful by-products result from using the water method to produce ions.

(2) Electron radiation method – this is based on a single negative discharge electrode needle. Millions of negatively-charged electrons are produced when a high voltage pulse is applied to the electrode. An advantage of this method is that no ozone is 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. The movement of electrons between the electrodes ionises the air in that same space. 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. 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. Dielectric materials do not conduct electricity while metallic electrodes are excellent conductors that transmit and receive 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 is pushed out of the purifier and re-circulated.

Very often, an ion source is inserted before the electrostatic filter to charge the airborne particulates. Charging the impurities make them adhere more effectively to the dielectric material.

Critics of this technology point to the production of harmful ozone in the ionisation process.

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. I will also be studying in greater depth 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.

To easily receive updates on new articles, subscribe to The Ionic Air Purifier Blog today.