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 weapons against invisible enemies seems the obvious answer. I find the intuitive logic appealing. But these days, finding a simple and quick solution is rare. Googling the subject unearths a ton of controversy. Obviously, I must resist the urge to go by intuition and grab the first ionic air purifier that I lay hands on. Effectiveness is important but safety is paramount in the criteria for selecting 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. Invisible ions of ionic air purifiers fall squarely in this realm.
In this article, I am laying out the roadmap as I look into the existing ionic air purifier technologies in the global marketplace. 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 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. In passive mode, impure air is drawn into the air purifier for 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. Interestingly, marketeers betray their lack of confidence in their own ionic air purifier technologies by combining both passive and active modes.
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.
Plasmaclusters of positive and negative ions encircle and latch onto harmful bacteria and viruses in a deadly grip. When clumping occurs, hydroxyl is produced. Hydroxyl, also known as nature’s detergent, is a powerful reactive species that destroys airborne particulates by plucking out hydrogen molecules from their organic structure. 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 real state of the natural environment. Proponents of negative ions believe that negative ions dominate the environment in these natural habitats and even insist that positive ions are 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. 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. 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. 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. 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. Large numbers of negative ions are produced as water droplets are split. 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. It is claimed that this method produces no ozone. It is claimed that this is because a “smaller” energy pulse is applied.
(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 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.
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. viruses and pathogenic bacteria) or non-infectious and non-contagious (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.
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. 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.
Impure air is drawn into the electrostatic purifier so that it passes over the dielectric material. Electrostatic electricity between the electrodes causes airborne particulates i.e.dust, smoke contaminants, etc, to adhere to the surface of the dielectric. Out of the other end of the purifier, cleaned air is recirculated.
Very often, an ion source is inserted before the electrostatic filter to charge 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. I have also not examined 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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Tags: air purifier, ionic air purifier, plasmacluster air purifier