Why quoted air filter efficiencies are completely misleading

 

Marketeers of traditional air purifiers have a tough job. There are lots of different air purifiers, so how to stand out from the crowd?

Well, a little like high end music systems, ‘measures of performance’ are created which appear important to potential buyers, but which are meaningless in practice, and then competing products can be compared and superiority claimed based on that same measure.

One such misleading measure is ‘filter efficiency’ where you often see a focus on the percentage of particulates (germs, pollens, mould spores, pet dander and house dust mite excretions) captured by the filter in the air purifier. For example, “my filter captures 99.97% of all particles and yours only captures 99.2%”, or “my filter captures smaller particles than yours does” and so on.

However, the fact is that such measures are pretty much meaningless in the real world.

But, you say, surely it matters how much of the particulates in the air, which may well be germs, allergens, irritants and other pollution, the device filters out?

My reply is that there are at least three major problems with using this measure of air purifier effectiveness, all of which make the number, be it 90%, 95% or 99.9%, pretty much meaningless!

The filter % measures the wrong thing

Measuring the percentage of particulates that are captured from the air passing through the filter measures only that, the percentage of particulates captured from the air passing through the filter. It doesn’t measure the percentage reduction of particulates in the air throughout the room, and the relationship between the two is tenuous at best!

The unfortunate truth is that the air in the room is constantly changing (typically it is replaced hourly with contaminated air from outside and elsewhere indoors), the air passing through the device is immediately remixed with unclean air in the room on exit and some of the air in the room never goes through the device at all. Some air never goes through the device because of insufficient air flow, temperature stratification and the formation of eddies (where the air in parts of the room rotates in a circular motion without ever moving through the air purifier).

As pointed out by the US Environmental Protection Agency (EPA);

"for typical room sizes, most portable air cleaners currently on the market do not have high enough air flows to effectively remove large particles such as pollen, dust mite and cockroach allergens"

The reason being that the larger (and heavier) particles, such as pollen, simply sink to the floor or onto other surfaces, ready to be re-distributed into the air when they are next disturbed!

If you model how air cleaners work (or measure their actual performance in practice) they can take hours to reach a stable minimum of pollution and that minimum is related to many factors, but only marginally to the efficiency of the filter itself.

Think of it this way, research has shown that a sufficiently powerful air filter, which captures 99.7% of particulates in the filter, effectively reduces the number of particulates in the air of a room, after several hours, by only circa 50%.

Changing the filter to one which captures only 90% will only have a marginal overall effect, perhaps limiting the reduction to, say, only 46%! Similarly, upgrading the filter to one which captures, say 99.99% of particulates, will result in only a marginal improvement, say to 51% overall.

50% or 46% or 51% doesn’t matter – none is nearly enough!

What does the percentage efficiency refer to anyway?

Well, the percentage efficiency actually refers to whatever the author wants it to refer to.

So, for example, a standard HEPA filter is rated to capture particles larger than 0.3 μm (micron), whereas a ULPA filter is rated to capture particles larger than 0.12 μm.   

The headline percentage effectiveness quoted is simply the proportion of particulates captured which are larger than the rated minimum, be that 0.3 or 0.12 μm.

Ultra fines and nano particles are smaller than even 0.3 μm, and may, or may not, be captured by the filter.

Ultra fines and nano particles can be both more numerous and more dangerous than larger particles as they are able to pass through human membranes and enter the bloodstream.

So, the percentage filter efficiency quoted means different things depending on the type of filter and the actual distribution of particulate sizes in the air.

What about gasses?

All of the basic technologies, HEPA, electrostatic and ionic, completely fail to capture or neutralise polluting gasses which can themselves be lung irritants and cause asthma attacks.

So, what is the answer?

The issues outlined above mean that, whatever the claimed filter efficiency, portable air cleaners have only a very modest effect on airborne particulate levels, and none on surface particulates, gasses or chemical pollution.

So, we at Airora have come at the problem of purifying the air in a typical room from an entirely new direction. Clearly, we need to do more than try and capture particulates in a device. We need to clean the air in the room directly and not just the air that passes through the device. To achieve this, we needed new thinking and new technology. 

The bad news is that it took us more than ten years. The good news is that we got there!

Airora is NOT a filter, it is a Hydroxyl Diffuser which emits an invisible Hydroxyl Cascade, as occurs naturally outdoors, indoors.

A molecular cascade reaction spreads the Hydroxyl Cascade throughout a room in seconds, without relying on air movement, thoroughly  decontaminating all the air and surfaces as it goes.

Airora benefits

• Airora is proven to safely destroy or neutralise, throughout an entire indoor space:

        all types of germs (including coronavirus)

        all types of allergens; including pollens, house dust mite, pet dander and mould

        all types of VOC and both organic and inorganic odours

        lung irritants from cleaning products, air fresheners, deodorisers, paint  and the like

        and most other harmful pollutants

• Airora is 1000+ times more effective, and far faster acting than any type of filter.
• The UK's Health Protection Agency measured a 99.9999% reduction of airborne germs in less than 5 minutes!
• Airora creates an active person to person infection barrier.
• Airora decontaminates surfaces as well as the air in a room.

 

You can find out all about Airora at airora.com

And contact us at support@airora.com