Purchasing an air purifier can be confusing, and you do get an awful lot of
information thrown at you when you visit the different manufacturing websites,
don’t you? How can you tell what’s what, and why do we need air filters anyway?
And how do air purifiers work? Is the air really that bad? Haven’t we been
breathing the same air for thousands of years?
Yes and no. First of all, we’ve been breathing the same air for thousands of
years, but we live in a symbiotic relationship with the plants around us – that
is, we rely on each other to survive. We breathe oxygen to live, and give off
carbon dioxide. Plants exchange carbon dioxide for oxygen, effectively
“exchanging” the air in a healthy relationship with us. This makes plants the
first primitive air purifiers on earth, and explains why scientists are so
concerned about the ecological balance on earth and the need for the survival of
rain forests and plants – they ensure our own survival as well by preserving
oxygen in our atmosphere.
Nature cleans the air in other ways as well – ozone (positively charged
oxygen molecules) is generated by waterfalls and thunderstorms. Ozone also
cleans impurities and particulates from the air naturally.
The Industrial Revolution and Air Quality
The industrial revolution made great strides in everything but air quality.
In fact, pollution such as emissions from automobiles, smog and pollution from
everyday chemicals like cleaning fluids, carpeting and paints enter the air
every day. In industrial settings, air purifiers clean the air before it is
released into the atmosphere in order to meet government requirements.
Today’s homes are also more energy efficient and cost effective, but to get
there they have become much more “closed in.” When they are this sealed up,
indoor pollutants are shut in so that today’s homes are actually two to five
times more polluted than outdoor levels! Obviously, air purifiers are essential
to improving indoor air quality to combat the effects of this stale,
Beginning in the 1980’s, medical practitioners began to take note of the
direct link between poor air indoor air quality and the increased incidence of
conditions such as asthma, allergies and recurring colds and upper respiratory
infections. The development of a variety of improved, scaled-down air filtration
systems for in-home use soon emerged.
How the Main Types of Air Purifiers Work
One of the most commonly used type of air purifier is also one of the first
developed, and is used in most hospitals and clean rooms. This is the HEPA
During the Manhattan Project in the 1940’s, the Arthur D. Little firm
developed the first HEPA filters in order to filter out very small particles
that had become contaminated by nuclear radiation in atomic bomb testing areas.
It was during this initial development that the HEPA standards were set at 0.3
microns, which could effectively capture condensed radioactive iodine.
The filters at that time were called “absolute filters,” and not called HEPA
(High Efficiency Particulate Air) until the filters were marketed in the 1950’s.
Today these filters are used by hospitals, surgical wards, biopharmaceutical
research labs, micro circuitry labs, and the aerospace industry for their
exceptional ability to control dust and particulates.
HEPAs remove 99.97% of particles of 0.3 microns or larger. For even more
intense filtration, there is an ULPA, or Ultra-HEPA filter, which filters out
99.99% of contaminants pass through the filter.
Obviously, something has to draw the air through the filter, and with HEPA
filters this is a motorized fan. This can make them noisy, which makes them an
annoyance to some people. A HEPA filter will need to be replaced every 12-18
months, depending upon how it is used and the interior environment of your home.
For instance, if you have pets, especially cats or dogs that shed a lot, you may
need to change it more frequently because of the dander. If there are smokers in
the house you will also need to change your air filter more frequently to ensure
However, for overall performance, nothing filters out or eliminates more
particulates than a HEPA filter, so it is a matter of balancing cost, sound
preference and convenience against your relative needs when choosing the right
model of air cleaner for your home.
Ozone Air Purifiers
Ozone is created in nature by everything from waterfalls to thunderstorms,
and is responsible for that fresh, clear smell after a heavy rain or storm has
passed. It’s nature’s way of cleaning the air. Ozone air purifiers essentially
do the same thing indoors by artificially mimicking the natural process that
Ozone molecules exist in the air all around us, and will react with any
particles they come into contact with, but are very unstable and tend to exist
in small quantities for short periods of time.
Ozone air purifiers work by using electricity to generate more ozone
molecules, which have one more oxygen (O3) than we normally have in the air (O2)
around us. Since ozone is highly unstable, one of the oxygen atoms is always
inclined to break away and find another molecule to bond to. This process causes
a chemical reaction which destroys odors and germs in the air and then converts
what is left of the molecules into harmless oxygen and CO2.
There is some confusion between ozone air cleaners and ionic air cleaners,
but there are some differences. With an ozone air purifier, the ozone that is
released into the air will be unstable and cause a reaction that will alter and
destroy certain germs, viruses, bacteria and molds. It does not, however, have a
collection plate where dirt or grime collects.
Ionic Air Cleaners
An ionic air cleaner also uses electrical charges to alter oxygen atoms in
the air, like an ozone air cleaner. But unlike an ozone cleaner, an ionic air
cleaner will rid the air your breathe of dust and pollen as well.
Ionic air cleaners negatively charge the air particles in a room, which will
cause a magnetic attraction to occur. The positively charged particles in the
air, such as dust, pollen and pet dander, will naturally be attracted to these
and they will “cling” to each other, creating a sort of magnetic bond. Particles
that form into bonds like this become too heavy to remain suspended in the air
and fall to the ground, where you will no longer be able to breathe them into
Vacuuming and regular dusting can get rid of these particles. In today’s
ionic cleaners, there are also fans that move the room air over negatively
charged metal collection plates that the positively charged particulates will
stick to. These can be regularly cleaned by simply wiping them with a soft
The original electrostatic precipitators were huge monsters used to control
pollution emissions from industrial plants. The waste by-products of a plant
were sent through large chambers that were charged by electrodes that acted as
enormous collection plates to attract the oppositely charged waste products
(such as dust, lead, sulfur, fly ash and other hazardous chemicals) from the
materials passing through, filtering out all harmful materials. Periodically,
the precipitators would be “tapped” so that these materials could be dumped from
the chambers into disposal units.
Home electrostatic precipitators also work on the theory of using a negative
charge and a positive charge to collect and retain particulates, however, the
charge takes place within the air purifier itself rather than in huge chambers,
and the dust and particulates are captured on metal filters that can be removed
and cleaned or replaced, getting rid of the need for a separate collection
chamber for the particulates.
With electrostatic filters, a small static charge is created that attracts
airborne particles as they go through a filter, capturing even those
particulates which are too small too be captured by the relatively loose weave
of the filter itself. Because of the looser weave, the air flow in an
electrostatic filter is very good, but the filtration is very effective because
of the electrostatic charge.
These filters do have to be carefully maintained and cleaned at least
monthly, and should be replaced every year for peak effectiveness. As the
filters do become dirtier, the air flow will become less efficient.
Finally, there are systems that combine two or more types of air purification
system. While these are usually more expensive, they can be worth the price if
you are looking for the best possible combination of features. For instance, an
air purifier that will kill viruses and bacteria like an ozone air purifier, but
will also effectively filter out dust and dander with a HEPA filter.