Ionic Air Purifier Technologies – Invisible Defence Shield or Science Fiction?

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. The weapons against such are very likely to be invisible to our eyes as well. I find the intuitive logic appealing. Unfortunately, there is no simple solution as google throws up an avalanche of controversy within seconds. 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. 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 especially so where the key reactive agent is invisible to the naked eye. Investigating ionic air purifier technologies falls within this ambit as the reactive agents are invisible ions.

In this space, I am providing an overview of the existing ionic air purifier technology in the global market. 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 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. Active generally means dispersive processes by which the impure air is penetrated and purified by the reactive agents. 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. They have been named as plasmacluster ions by Sharp Corporation, the Japanese corporate powerhouse that invented them.

Positive and negative plasmacluster ions actively surround harmful bacteria and viruses in a deadly embrace. When this happens, 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. 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. Currently, this technology dominates market share but it is 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. The positive charges are continually attracted to the negative charges of the ions until sheer mass makes them sink to the ground. Thereafter, simple vacuuming removes these impurities. Weighing down the particulates does nothing to destory them, according to critics, and merely walking on them causes the air to be polluted again.   

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. It is claimed that no harmful by-products are produced by the water method.

(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. 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. This causes the movement of electrons between the electrodes thereby ionising 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. biological compounds that may be infectious or contagious (e.g. pathogenic bacteria and viruses) or non-infectious and non-contagious (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.

Critics of POC zoom in on the power effects of hydroxyl, claiming that they cannot differentiate between the organic structures that make up molecular contaminants and our lung tissue, eye cornea or nose membranes.

Electrostatic Filter

This technology appears to have originated in heavy industries which produced abundant pollutants. The typical electrostatic filter ionic air purifier includes two electrodes sandwiching a porous dielectric material. A dielectric material does not conduct electricity while metallic electrodes are good conductors that transmit or receive electricity.

Impure air is sucked into the electrostatic purifier and passed over the dielectric material which acts like a sieve. Electrostatic electricity between the electrodes causes airborne particulates i.e.dust, smoke contaminants, etc, to adhere to the surface of the dielectric. Purified air is pushed out of the purifier and re-circulated.

Frequently, an ion source is planted just before the electrostatic filter to electrically charge the airborne particulates. These impurities, so charged, stick 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.

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