How a Filterless Air Purifier Works

In the interests of eliminating fan noise as well as the need to clean and replace various filters, air quality technicians have been working on a filterless air purifier. Four different types have been developed to date:  electrostatic, ionic, photocatalytic and plasmacluster. These are explained below, to highlight their advantages and areas of concern.

Electrostatic Air Purifier

The first to claim to be that apparent oxymoron, the filterless air purifier, were the electrostatic air purifiers. These were developed and patented in 1996. The principle behind these air purifiers is a system of electrostatic attraction. A fan draws air into the purifier. Particles in the air are then ionized (given an electronic charge) to a negative polarity. Long thin, positively charged plates, called electrostatic precipitators, pull the charged particles out of the air and retain them.

The advantages are that filters are not used for the main work of air cleaning, the fan is small and relatively quiet, and the system can operate without returning any harmful byproducts to the cleaned air.

However, electrostatic air purifiers have four recognized problems: first, using a fan to draw in air, they are not silent, and can disturb sleep if used in a bedroom. Second, the system is primarily effective on large particles over 1 micron in size, so smaller and more dangerous particles like mold spores are not removed. Third, the method of removing particulate matter, only to store it in the purifier, layers the plates with contaminants which must be washed regularly. Cleaning the plates restores these undesired particles to the air, or adds them to the water supply.  Fourth, the electrostatic air purifiers test as less efficient than HEPA filtration, at 95 percent of airborne particle removal compared to HEPA filters' 99.7 percent.

Ionic Air Purifiers

These air purifiers send out charged air molecules (ions) into the air. These collide with airborne particles and attract them together in masses heavy enough to fall to the floor or other horizontal surfaces. While this does make them filterless, ionizers do not truly remove the particle masses, odors or chemicals from the room completely. During the ionization process some ionic air purifiers give off ozone (ionized oxygen), a harmful byproduct.

Photocatalytic Oxidation (PCO)

The first truly filterless air purification system is photocatalytic oxidation. An ultraviolet light source, often one light bulb, activates metal semiconductors, which produce oxidating compounds that can kill nearly microscopic particles, chemicals, and odor-causing bacteria. While they can be used without filters, often a filter will be added to prevent large particles from collecting in the unit.

Plasmacluster Ions

Each plasmacluster has two ionizers to create both negative and positive airflow, and create oxidizing molecules that are carried on air moisture to eliminate particle contaminants and neutralizing bacteria and viruses. Again, a HEPA or other filter often is included to block the largest particles from entering the air purifier.

So far the HEPA filter, developed in the 1940s for use in gas masks, is the standard against which all other air purifiers are measured. Filterless air purifiers cannot yet match that standard.