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Air purifier technologies
Several different processes of
varying effectiveness can be used to purify air. Different processes may
remove different contaminants, so there is advantage in using more than
one process in a purifier.
Filter-based purification traps airborne
particles by size exclusion. Air is forced through a filter and
particles are physically captured by the filter.
HEPA filters can, by definition, remove at least 99.97% of
0.3-micrometer particles, and are usually more effective for particles
which are larger or slightly smaller. They are effective down to 0.01
micrometers in many cases, but become very ineffective for particles
smaller than 0.01 micrometer. In dusty environments, a HEPA filter may
follow an easily cleaned conventional filter (prefilter) which removes
coarser impurities so that the HEPA filter does not need to be changed
or cleaned frequently. HEPA filters do not generate ozone or other
harmful byproducts.
Activated carbon is a highly porous material that can absorb
volatile chemicals on a molecular basis, but does not remove larger
particles. It is important to note that the absorption process when
using activated carbon must reach equilibrium thus it may be difficult
to completely remove contaminants. Activated carbon is merely a process
of changing contaminants from a gaseous phase to a solid phase, when
aggravated or disturbed contaminants can be regenerated in indoor air
sources.Activated carbon can be used at room temperature and has a long
history of commercial use. It is normally used in conjunction with other
filter technology, especially with HEPA. Other materials can also absorb
chemicals, but at higher cost.
Air Ionizer purifiers use charged electrical surfaces or needles
to generate electrically charged air or gas ions. These Ions attach to
airborne particles which are then electrostatically attracted to a
charged collector plate. This mechanism produces trace amounts of ozone
and other oxidants as by-products. Most ionizers produce less than 0.05
ppm of ozone, an industrial safety standard. There are two major
subdivisions: the fanless ionizer and fan-based ionizer. Fanless
ionizers are noiseless and use little power, but are less efficient at
air purification. Fan-based ionizers clean and distribute air much
faster.
Ozone
As with all
health-related appliances, there is some controversy surrounding the
claims of certain companies, specifically involving ionic air purifiers.
Particularly, some ionic air purifiers generate ozone, an energetic
allotrope of three oxygen atoms, and in the presence of humidity, small
amounts of NOx. Ironically, people who have asthma and allergy are most
prone to the adverse effects of high levels of ozone.For example,
increasing ozone concentrations to unsafe levels can increase the risk
of asthma attacks. Due to the below average performance and potential
health risks, Consumer Reports have advised against using ozone
producing air purifiers. Ozone Generators used for shock treatments
(unoccupied rooms) which are needed by smoke, mold, and odor remediation
contractors as well as crime scene cleanup companies to oxidize and
permanently remove smoke, mold, and odor damage are however considered a
valuable and effective tool when used correctly. Ozone, unlike other
harsh chemicals used to clean odors, will revert back to O2 (oxygen)
after about 30-40 minutes and will not leave behind any residue or harsh
byproducts.
In September, 2007, the California Air Resources Board announced a ban
of in-home ozone producing air purifiers. This law, which will take
effect in 2009, will require testing and certification of all types of
air purifiers to verify that they don't generate too much ozone. This
ban does not affect shock treatment ozone generators however. Studies
indicate that some ionic air purifiers produce ozone at 3.3 to 4.3 mg.
Ozone generators used for shock treatments on the other hand produce
over 3000 mg/h, the amount of ozone needed to create a "shock treatment"
over a 6 hour period in a 100-200 sq. ft room. The ozone generators
which are subject to this ban use ceramic Mica plates that produce
300-400 mg/h of ozone and are intended to be used indoors in occupied
rooms.
Choosing an air purifier
When selecting air purifiers, consumers are
influenced by several factors besides cleaning ability. These include
possible hazardous gaseous by-products, noise level, frequency of filter
replacement, electrical consumption, and visual appeal. Ozone production
is typical for air ionizing purifiers and has received much attention
recently. Although high concentration of ozone is dangerous, most air
ionizers produce low amounts of ozone (<0.05 ppm). The noise level of a
purifier can be obtained easily through specs chart and is usually
reported in decibels (dB). The noise levels for most purifiers are low
compared to many other home appliances. However, purifiers are expected
to operate over long periods of time. Therefore, even a moderate level
of noise can be disturbing to some people. Frequency of filter
replacement and electrical consumption are the major operation costs for
any purifier. There are many different types of filters; some can be
cleaned by water, by hand or by vacuum cleaner, while others need to be
replaced every few months or years. Some purifiers are certified as
ENERGY STARŪ and are energy efficient.
HEPA technology is often used in portable air purifiers as it removes
common airborne allergens. The US Department of Energy has rigid
requirements manufacturers must pass to meet HEPA requirements. The HEPA
specification requires removal of at least 99.97% of 0.3 micrometres
airborne pollutants. Products that claim to be "HEPA-type", "HEPA-like",
or "99% HEPA" do not satisfy these requirements.
Other factors that buyers consider when purchasing an air purifier are:
the area coverage; the Air Changes Per Hour, which indicates how
frequently the air purifier can exchange all the air in a given room;
the Clean Air Delivery Rate, which determines how well air has been
purified; energy usage; and the cost of the replacement filters.
If you need expert advise for you specific concern please do not
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Certified Indoor Environmentalists
