An Overview of Air Purifier Technology and Brands

Air purifiers remove pollutants from indoor air. While this is a simple statement the technologies, pollutants and medical conditions involved are quite complex. The technologies used in systems that are sold in the United States range from very effective through moderately effective to downright dangerous! The pollutants that are of concern include natural problems like pollen and mold spores as well as chemicals, microorganisms and odors. The medical conditions that require the use of purifiers include allergies, asthma, Multiple Chemical Sensitivity (MCS), weakened immune system, and simply a dislike of odors. In this article we are going to start with a review of air purifier technologies available and talk about what indoor pollutants that are involved.

Before you consider using an air purifier there are a couple of actions that you should take. First and foremost you should attempt to remove or reduce the source of the pollution. If your dog sleeps in bed with you it is unlikely that any number of products are going to help with your dog allergy. If you have a smoker in the house make them go outside to smoke. Secondly, if you have a forced air HVAC system you must change the furnace filter at least every six months. If you take these steps to eliminate the source of your indoor pollutant you greatly enhance the ability of your indoor air purifier to effectively eliminate the pollution.

Technologies
Most of the technologies used in air purifiers are used in tandem with one removing particulates and the other removing chemicals and odor. We will discuss each of the technologies separately and then put them together when we discuss the products.

HEPA
HEPA stands for "high efficiency particulate arresting" or by some "high efficiency particulate air". These filters are used in most of the systems sold today and are made of a paper thin maze of fibers. As particles in the air pass though this maze they snag on one of the fiber and are held in place. Because these fibers are so dense the airflow through a sheet of HEPA filter is very constricted. Therefore the filter material is folded back and forth to present a very high surface area to the air stream and thus to allow sufficient airflow to make a HEPA air purifier affective. Typically HEPA filters will filter particulates of 0.03 micron size with an efficiency of 99.97%. However, the less expensive HEPA air purifiers often are subjected to a lot of blow-by. This means that air under power from the fan can move around the filter rather then though it. Since none of the manufacturers except those at the high end quote blow-by numbers understanding how efficient your air purifier is can be problematic.

Activated Carbon
Activated carbon is used to adsorb (not absorb) chemicals from the air flow of air purifiers. This works by providing tremendous surface area to which these chemicals can attach held by Van der Waals force. Eventually the entire surface area is cover with a film of chemical and the activated carbon is no longer effective. This technology has been used in products for many years to remove chemicals and odors. The same system is used in many water purification systems.

Electronic or Electrostatic Air Purifier
Air purifiers using electrostatic technology are often used in industrial applications or commercial applications like in restaurants or bars. In home applications it is usually seen in whole house filters. Overall they are much the same as HEPA filters because these systems remove particle pollution but not chemicals. All of these products work on the same principle. The air is drawn though the system with a fan. Then there are two electronic stages. The first stage charges any particles that pass though in one polarity. The second stage is the opposite polarity so that the particles are electronically “stuck to” the second stage plates. After awhile the particles will build up so thickly on the second stage that there will be an arcing or popping sound. Then the plates must be cleaned. While the second stage of an air purifier must be made from plates to provide a landing zone for the particles the first stage may be either plates or just charged wires. Care must be taken in selecting purifiers that use this technology because there is a possibility of creating Ozone which is dangerous.

UV
Ultraviolet light used in air purifiers is typically radiation in the range of 150 to 300 nanometers. It works by causing adjacent thymine molecules in DNA to unravel or dimerize. Thus any microorganism that gets sufficient exposure to this radiation dies or at least stops reproducing. This includes viruses, bacteria and spores from mold. While this is an efficient air purifier technology for addressing microorganisms it is relatively ineffective in addressing either chemical or particulate pollution and is therefore, like activated carbon, used in combination with other technologies. Care must be taken to change the bulbs in these systems on a regular basis because they have a fixed life and will continue to radiate visible blue light long after they have stopped generation UV radiation.


Ozone
Ozone is a molecule made of three oxygen atoms. Because Oxygen is stable with two oxygen atoms the Ozone molecule gets rid of the third atom as soon as it can. So, any chemical that it meets will become oxidized. This process used in an air purifier is effective at removing smells from the air but the chemical itself has been found to be irritating to human lungs and deadly for small animals. Also the compounds created by this process may be more dangerous than the initial compound. The FTC has forced all manufacturers of Ozone air purifier units to stop making any medical claims. The state of California has banned the sale of ozone air purifier products completely. Unfortunately many of their dealers continue to promote these devices to people with asthma and allergies to the detriment of these people. Air purifiers sold with the nomenclature of “Living Air”, “Active Air”, and “Natures Air” all use ozone and are dangerous around people. As an aside, there are a number of ozone based industrial air purifier products that can be applied effectively to clean up sewage smells and other industrial requirements where humans are not present.

Ionic Breeze
Ionic Breeze is a heavily marketed technology that is Trademarked by Sharper Image. All true third part tests have shown them to be ineffective because they do not have a fan. Theses air purifier units use electrostatic technology but count on the charge differential between the two sets of plates to move the air. While this is sufficient to flutter ribbons it will not effectively move the air from the entire room though the air purifier. In addition they have had to add an optional filter to remove the dangerous Ozone these air purifiers produce.  Sharper Image has lost a class action suite brought because these air purifier products don't work.

Ionizing
Air purifier systems that creates negative ions have been used effectively for years in poultry farms as a way to keep the dust from thousands of birds under control. The negative ions charge small particles that then tend to clump together and become heavy enough to fall from the air. In addition these charged particles will also “stick” to any surface provided. There are several downsides to this technology. First, the walls of you house will actually darken as the particulates in the air adhere to them. Secondly, the process of creating negative ions in an air purifier often also creates ozone as a dangerous byproduct.

The Pollutants Encountered by Air Purifier Products
There are three types of pollutants that are addressed by air purifiers; particulate, microorganisms, and chemical. In our review of the technologies above we tried to be specific as to which of the technologies employed in products is effective with which pollutant. Now we will discuss the various pollutants that are common for indoor purifiers to address.

Particulate pollution can come from a number of sources. The most pervasive is outdoor air pollution made famous by major cities like Los Angeles and Houston. This pollution is generated primarily by combustion that creates particulates. This combustion ranges from tobacco smoke to diesel engine fumes. While the larger 10 micron particles are tracked by pollution agencies as PM10, the smaller 2.5 micron particles are thought by the American Lung Association to cause the greatest distress among people with respiratory conditions. This smaller particle pollution is termed PM2.5. Fortunately while this is a small particle size it is large with relation to an air purifier using either HEPA or electrostatic technologies which address particle sizes of 0.30 microns and smaller.

Pollen is probably the next most prevalent problem for air purifiers to handle. In addition to being a particulate, when pollen lands on sensitive membranes it can trigger mast cells to produce histamine. This makes an allergenic miserable in more ways than just a runny nose including headaches and loss of sleep. Pollen can range in size from 5 to 50 microns in size with the common culprits being grass and weed pollen that is in the upper end of this range. Thus any of the air purifier technologies that are effective with particulates will remove pollen from the environment.

Microorganisms are usually addressed by systems in cases where people may have weakened immune systems. This includes the very young, the very old, and those that are in hospitals and nursing homes. While HEPA air purifier technology will filter particles as small as bacteria it is UV technology air purifier systems that  disable these diseases in hospitals, nursing homes, extended care facilities, day care centers and nurseries.

The number of chemicals that can show up in the environment are too numerous to detail. They can come in with new carpet, paneling, cleaning supplies and outdoor pollution. Air purifier that employ activated carbon are generally used to address chemicals. However, if the actual chemical is known many firms can recommend air purifier media that specifically targets that chemical or family of chemicals. Avoidance is always best. So, as we stated at the beginning of this article try to clear the area of the chemical prior to exploring air purifiers.