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. 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. It is quite clear that the urge to rush out and buy an ionic air purifier must be suppressed at the moment. 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. This is especially so where the key reactive agent is invisible to the naked eye. My investigation of ionic air purifier technologies falls within this realm, as the reactive agents are ions that are invisible to our eyes.

In this space, I am providing an overview of the existing ionic air purifier technology in the global market. Trying to understand the science behind the technologies seems to be the logical place to begin searching for the ideal ionic air purifier. The creation of a powerful invisible defence shield against airborne molecular contaminants is increasingly taking centrestage. 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. 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. They have been named as plasmacluster ions by Sharp Corporation, the Japanese corporate powerhouse that invented them.

Sharp Corporation’s marketing efforts focus on the ability of plasmacluster ions to surround and cling on to harmful airborne bacteria and viruses. When clumping occurs, hydroxyl is produced. 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. 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. In contrast, proponents of negative ions technology insist that negative ions fill natural habitats and that the presence of positive ions is harmful. As I progress with my research, I shall be looking for independent scientific studies that support either of these two opposing views.

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. 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.

Apparently, there are a number of ways to produce negative ions. It is critical to know the various methods as each may have different by-products, some harmful and some which are not. 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. This simple action results in the splitting of water droplets, causing the production of large numbers 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. The simple application of a high voltage pulse to the electrode results in millions of negatively-charged electrons being produced. An advantage of this method is that no ozone is produced. 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. 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. Hydroxyl, nature’s detergent, is the key reactive agent in POC technology.

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.

Comprehensive defence is the key strength 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. 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 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. In the most common electrostatic filter arrangement, there is a porous dielectric material positioned between two electrodes. Dielectric materials do not conduct electricity while metallic electrodes are excellent conductors that transmit and 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 between the electrodes causes airborne particulates i.e.smoke contaminants, dust, etc, to stick to the dielectric surface. Purified air is pushed out of the purifier and re-circulated.

An ion source is often placed before the electrostatic filter to impart an electric charge to the airborne particulates. Charging the impurities make them adhere 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 have also not 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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