Passive technology always employs some form of filtration and always requires that contaminates find their way to the filtering device. A filter is to the airborne contaminate what the spider's web is to the insect. No matter how big or how little, regardless of the size or design, a germ or bug may fly freely about the air space unless or until it is caught in the trap of the filter fibers or the web. If it is small enough to slip through the fibers or strong enough to wriggle loose, it is free to fly about again. Even if a filter were 100% effective at trapping and keeping 100% of the contaminates 100% of the time (which it never is or can be), its effectiveness would be limited only to those contaminates which physically pass through the filtering mechanism, leaving all the unfiltered air to remain contaminated.

Does this represent the air "purifier" you are depending upon?  If so, your technology is full of holes.

A passive air purifier's ability to clean a room, like a vacuum cleaner, is limited to its physical location and its ability to move dirt toward its intake.

Another analogy would be that of a vacuum cleaner in a room saturated with dust and dirt - on the floor and carpet, the furniture, the drapes, the bookshelves, everywhere. Giving the vacuum credit for being 100% efficient (which it can never be) at removing dirt from any air that it suctions, put the vacuum in the room anywhere you like, high or low, and turn it on at maximum power. Regardless of what it does to the air and contaminates once they enter the machine, it's ability to clean the room is limited to its physical location and its ability to move dirt toward its intake. Because of its inherent design technology, even powered by a jet engine, it will never clean the room completely. There will be wind current eddies and dead spots, just as in a running stream, that will harbor materials which will never see the inside of a passive air filter. (The kind of power it would take to get all the dirt into the vacuum would be enough to suck up the furnishings and carpet as well. Plus, the noise would be unbearable!)

Among the so called air "purifier" manufacturers, the competition is fierce. Some do speak of "CFM" (cubic feet per minute), the measured amount of air that can pass through such a system over a given period of time. Some companies or models use a germicidal light or other method to try to sanitize or sterilize the air which makes it through the device. At least one make boasts an incinerator to burn up contaminates as they pass through. But regardless of brand, model, size, capacity, or features, the hottest area of contention, however, is the efficiency of the filter/s themselves, often offered in multiples or multi-stages. A term often heard among air device manufacturers is that their system or filter meets "HEPA" standards. Developed after World War II to trap atomic dust particles, "HEPA" stands for "High Efficiency Particulate Arrestance". It generally means that the filter will capture 99.97% of particulates down to those as small as .3 microns, which includes some bacteria, fungal, and other opportunistic micro biologicals. At first glance, that is pretty impressive. To be sure, for all those people who have gained some measure of relief by being able to breathe air whose contaminates have been reduced to some degree, HEPA and passive air purification has been a blessing. But the results have often been inconsistent and not stable enough to be accurately predictable from one venue to another or from one piece of equipment to the next. Even among those conforming to HEPA standards there will be discrepancies and deficiencies depending upon when the evaluation tests are run relative to the buildup of the load in the filter itself. Was the filtering medium fresh? Were the numbers achieved and averaged over any particular length/s of time and filtering loads? What were those parameters? How dirty was the air that went into the device? What was the measurable air flow at the time of the test, and how did it compare to later when the filter was much more full (dirtier)? What most have observed about other types of filters, be they vacuum bags or oil or air filters for cars, is also true of HEPA filters. It stands to reason that a filter works by letting air pass through its openings, whether they be small or large (although the surrounding fibers are an impediment). As particles are caught on the surfaces of the filter's fibers, they bridge over the openings through which air is supposed to pass and clog them. As those openings become clogged, the number of remaining openings diminishes. Hence, the more that filtered particles build up on the filtering surfaces, the less efficient will be the flow of air through the filter. The slower the air stream through a filter, the fewer the particulates which will be taken out of the stream flow and the less will be the efficiency of the device. Unless a system's rating is based upon its minimum efficiency under loaded conditions, any filtering device will function at its best when new or equipped with fresh filtering media and drop off (often exponentially) as it does its job and the load increases. While diminishing filter capacity concerns are a consideration, they do not represent the main weakness of passive technology. Nor is the issue primarily the relative power of the air moving device (fan horsepower, speed, blade efficiencies, etc.) The fundamental deficiency is that the technology is utterly dependent upon contaminates finding their way into the filter where they can be trapped. Experience has shown that not all contaminates cooperate in this effort. And beyond those considerations, there may remain questions as to the viability of pathogens and mold spores, trapped to be sure, but which might still be able to pose a threat where they accumulate in the filtering device or may find themselves scattered when the filters are removed, replaced, or cleaned.

All of the above having been said and factored, there is one final concern, but it is staggering. It must be understood that not all HEPA filters are created equal.  And it must also be acknowledged that all HEPA filters do not perform at the same level or efficiencies.  Some do better earlier into their useful lives, while others may function not as well initially but be more consistent over their service life. Be that as it may, as of this time in history, the HEPA filter as a class seems to be the best of the best as far as filters and filtration technologies are concerned (all of which are passive and, consequently, limited as discussed). One huge fact remains, an issue having to do with the sheer physics of the problem. While the list of particles and particle sizes filtered out by HEPA compliant filters appears to be impressively grand (all sizes down to .3 microns), 98.5% of all particle counts are <.5 microns! As tiny as these particles are individually, their collective mass comprises 6% by weight of all the particles in the air. If at first glance 6% of the weight of collective particulates may seem somewhat small, think of the massive amount of weight and the large particle sizes one would find in a full vacuum container bag or an air filter. Depending upon the vacuum or filter type, three to six percent (or even more) of all the particulates one would want cleaned from the breathing space would pass all the way through the filter and back out again, even if the filter device could force all the particles in the room to enter its orifice. Then remember that it is the small particulates (<.5 microns) which make us ill.

Passive air purification technology, regardless of how efficient, leaves unresolved any items or issues not passing through its system, and, is, therefore, an inferior and aged approach if utilized alone.

Summary of the common problems faced by ALL Passive Technologies

X	IMPOSSIBLE for ALL air to get TO them and THROUGH them.
X	FILTERS and PLATES become constant source of POLLUTION, HIGH MAINTENANCE, and COST.
X	FILTERS and PLATES have LIMITED EFFECT on VOC's, ODORS, BACTERIA, MOLD, and MILDEW which pass through the systems.
X	FILTERS and PLATES have NO EFFECT on VOC's, ODORS, BACTERIA, MOLD, and MILDEW on SURFACES in the room.
X	Where UV lights are used, they affect only the specific areas onto which they directly shine.
X	VENTILATING is extremely expensive and limited in its effectiveness.
X	If PASSIVE technology is so effective, WHY ISN'T THE PROBLEM SOLVED?

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2.	Active technology.

Although they were once small enough to remain airborne, electrically charged ions have attracted enough particulates together so that they must fall out of breathing range.

Like aircraft too heavy for their engines or jumbo jets out of fuel, the particulates stagger and fall to the floor, colliding, collecting, and clumping with others on their way down. Rather than passive, this is active technology which fully sweeps and cleans the interior air spaces and penetrates into cavity areas. Ions also adversely affect the health of pathogens while improving the feeling of well being among people and animals.

More on ionization here Negative ion studies How negative ions clean up the air

b. Stage Two -- Quad Oxidizing Plasmas. Stage two involves the simultaneous use of another technology which introduces a plasma of multiple, "friendly" oxidizers into the living space. (They are known as "friendly", for, just as in nature, whether or not they have had the opportunity to do their assigned duties, within about thirty minutes, they revert right back to molecules of H2O from whence they were derived from the air in the atmosphere.) Combining high intensity UVX light with a specially developed rare metal hydrophilic coating on an engineered matrix, Radiant Catalytic Ionization™ (RCI™) reduces airborne contaminants, and odors while creating super oxide ions and hydro-peroxides. While active, these oxidizers also have the potential of infiltrating behind wall cavities, and wherever they go they strip the very hardy shells off of mold spores, fungi, and numerous other pathogens and contaminants, killing them outright or rendering them very susceptible to destruction. By engineering the proper light wavelengths into the RCI™ cell, what develops is a highly effective system designed to utilize 254 nm hv germicidal UV light. Falling between visible UV light and invisible X-Rays in the light spectrum, UVX makes use of the same oxidation and ionizing properties of light as naturally occurring sunlight. This technology takes advantage of these ionizing properties and combines them with the photo catalytic reactions of specific rare and noble metals to create Radiant Catalytic Ionization™ (RCI™). This innovative use of light is what makes RCI™ so effective.

KSU RCI Charted Test Results