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Air
Cleaner Technology
Before purchasing an air cleaner, make sure
you understand the technology used by the air cleaner and the potential
issues that may be inherent in that technology which could effect the
efficiency of the air cleaner and your health. Some technologies
are ineffective and actually contribute to poor indoor air quality by releasing contaminants
back into the air or releasing toxic chemicals or charged particles that
can be trapped in the lungs. Many air cleaners may use multiple
technologies in their design.
- These units use an electronic
field to help trap particles. Some manufacturers refer to ionization as a "High Energy
Field" or "Electrical Energy Field". There are primarily two types of electronic
air cleaners. These devices are not recommended for healthy air
cleaning.
-
Electrostatic Precipitators
- As the
air particles pass
into the air cleaner, an electronic charge is given to them through a high
voltage (also called ionization). The charged
particles are then attracted to a series of flat plates or low efficiency
filter media with an opposite
electrical charge. These units can either operate as fanless (plate type) or
with a fan.
- Ion
Generators - These devices charge particles, but
unlike electrostatic precipitators,
these units don't remove
the particulate matter, they only cause them to accumulate and
attach themselves to various surfaces around the room.
They claim to be air cleaners by removing suspended particles
from the air.
- Issues:
-
Beginning efficiency is low
compared to mechanical filtration and rapidly loses
efficiency. As the charged plates or filter media collect
particles, the electrical attraction diminishes because the
surfaces become covered with contaminants. This reduces the
ability of the air cleaner to capture more particles.
-
Units that capture particles
require high maintenance, weekly cleaning or short filter
replacement periods. Plates need to be constantly cleaned to
remove particle build-up to maintain efficiency. Filters
need to be constantly replaced to keep the static charge.
-
These devices generate ozone
which is a known lung irritant. Various state and federal
agencies warn that ozone generating devices should not be
used in the home. (see Ozonation
below).
-
Charged particles that are not
captured can re-enter the room where they can build-up and
soil the surfaces throughout the room. Ion generators
specifically work on the principle of depositing particles
on room surfaces. Additionally, these escaping charged
particles can be inhaled into the lungs where they become
lodged and difficult to expel. In a study referenced by the
US EPA published in Atmospheric Environment, "Control of
respirable particles in indoor air with portable air
cleaners," experiments have shown a linear increase in
particle disposition in the respiratory tract with charging,
therefore ion generators may not reduce the dose of
particles to the lungs.
-
Captured particles on plate type
devices can be blown back out into the room because they are
not physically held in place. When the device is turned off,
such as when cleaning, the electrical charge is stopped and
the contaminants can be re-released into the room or inhaled
during movement and maintenance periods.
-
These devices may emit loud
arcing noises and the US EPA has reported in a publication
"Residential Air Cleaning Devices" that electronic air
cleaners have been reported to produce fine particulate
material.
- Ultraviolet
light (UV) is not visible to the human eye. It refers to the
part of the wavelength spectrum below visible violet light and
above x-rays and gamma rays. All light is a form of
electromagnetic radiation. The distinguishing aspect of UV light
is the wavelength which is longer than x-rays but shorter than
visible light. This technology is commonly used in a variety of
healthcare and water quality applications where the control of
microorganisms is desired. There is no reliable documentation to
demonstrate UV effectiveness in air cleaner applications. This
technology is not recommended for air cleaning.
-
Issues:
-
The effectiveness of ultraviolet light at destroying
microorganisms such as bacteria, mold and viruses depends on
the intensity of the light and duration of time the UV light
is contacting the microorganism. Air travels at tremendous
speed through an air cleaner. There is little contact time
of the UV light on particles. Additionally, biological
contaminants may be covered with particulates in which the
UV light will never actually shine on the microorganism to
have an effect.
-
Different microorganisms require
different light intensities and contact duration to kill
them. This is difficult to control in a light chamber where
the particles can be at various distances and locations from
the UV light source.
-
UV Light gets weaker over time
and requires regular maintenance.
-
UV light can degrade the filter
media and other components of the air cleaner.
-
The Centers for Disease Control
(CDC) states that UV light in hospitals does not add to the
effectiveness of HEPA mechanical filtration.
- Air
Washing
- These units consist of an open
water holding tank, a fan and a series of plastic disks
partially submerged in the water that are turned by a motor. A
fan blows air over the wet disks as the disks are turned in the
water. The wet surface of these disks release water vapor into
the air and also pick up particles in the air from the fan's
airstream. As an air cleaning system, these units are not
recommended.
-
Issues:
-
These units are not
effective at removing small particles. Some manufacturer's
literature indicates removal of particles down to 10 microns.
Other product manufacturer's claim lower particle capture when
using ionization technology. 90% of all air particles are below
0.3 microns and it is these smallest particles that are
potentially the most troublesome to health.
-
The open water
holding tank is susceptible to the growth of microorganisms such
as mold, bacteria and fungi that could potentially be released
into the air along with the water vapor. Manufacturers
recommend the use of biocide and fungicide additives to control
growth that could potentially be introduced into the air along
with the water vapor it is dissolved in.
-
These units require constant
maintenance and cleaning. Water has to be added daily, additives
to control microorganism growth have to be used continuously and
the units have to be completely cleaned every one to two weeks.
-
Incineration
- Units that incorporate
incineration technology claim to clean the air by killing
microorganisms. There is a heating element within the unit that
reaches temperatures over 400°F. There are no fans, air moves
through the unit by the process of convection in which the
heated air within the unit rises out of the unit and thereby
pulls more air into the unit. Particles within the air carried
through the unit are burned at high temperature. This technology
is not recommended for effective room air cleaning.
-
Issues:
-
These units do not
trap particles. They are not a comprehensive solution to clean
air. Particles are incinerated at high heat within the unit and
are either retained in the unit or they continue in the airflow
out of the unit. Burned particles (deadened cell parts) that
exit these units can become airborne and then be inhaled into
the respiratory tract where they may trigger asthma and allergy
symptoms.
-
There is very little
air flow through these devices because of the limited nature of
natural convection air flow. The manufacturer's stated
information indicates about 8 cfm of air movement. Since these
units work through contact with particles carried in the air
through the unit, low air flow means low contact with
pollutants.
-
These devices can
get hot. Manufacturer's information indicates temperatures can
reach 144°F in the top center of the device. It takes 2 seconds
to produce a 1st degree burn at 140°F and 5 seconds to produce
second to third degree burns.
-
Effectiveness testing of these units
are difficult. Microorganisms are affected by numerous factors
and vary up and down constantly depending on changes in the
local environment. Testing is done with out comparison to other
technologies under the same test conditions. Without comparison
testing of several technologies under the same test conditions,
you can not effectively state a device is best at controlling
microorganisms.
-
Long term effectiveness may be an
issue and the build-up of incinerated particles within the
devices. These devices have a limited lifespan and wear out. No
information is provided on product effectiveness over several
years. These devices are not user serviceable for maintenance
and can not be opened. According to the instruction manual,
the lifespan of these devices is 5 years. After which you
must throw your $300 product away!
- Charged
Media Filtration
- Many air cleaner manufacturers
inappropriately use the word HEPA in their description of air
filters that do not meet the industry standard for HEPA
efficiency of the filter. This is most commonly seen in charged
media type filters. The less
dense meshwork of synthetic fibers of these filters have been
given an electrostatic charge during manufacture. It is this
electrostatic charge that helps to attract particles. They may
be used alone or in combination with another technology like
ionization. This air cleaning technology is not recommended.
- Issues:
-
Efficiency level is helped
significantly by the electrostatic charge of the filter
fibers. As the charged fibers of the filter media
collect particles, the electrical attraction diminishes
because the surfaces become covered with contaminants. This
reduces the ability of the air cleaner to capture more
particles.
-
Short filter replacement periods
are necessary to keep filter efficiency high. This can be a
high maintenance cost. This filter material is less dense
than a true HEPA filter, so particle escape becomes a major
concern.
- HEPA
Mechanical Filtration
-
 These units are the best for
capturing particulate matter. They utilize a filter media with very high
efficiency ratings. We can see to about 10 microns (one micron is 1/25,000
of an inch). A High Efficiency Particle Arresting filter or
HEPA
filter can capture 99.97%
of particles as small as 0.3 microns (1/83,000 of an inch or 0.00012). A HEPA filter also captures particles
below 0.3 microns and can be 95%-99% effective at capturing particles below
0.3 microns in size. These filters were originally designed
to trap microscopic particles such as radioactive dust in atomic plants and are commonly used for critical
environments like hospitals, clean rooms and lead paint/dust abatement projects.
It is necessary that an air
cleaner be a sealed and gasketed system to take advantage of the
HEPA efficiency at removing particles from the air. Critical
design details are important in achieving high air cleaning
performance. If an air cleaner using a HEPA filter is not
properly designed, air will bypass the filter as static pressure
pushes against the filter and allow particle escape. Most air
cleaners on the market include HEPA filters as a sales and
marketing tactic, but fail to achieve HEPA performance. You
won't find HEPA performance air cleaners at the local mass
merchandise store.
Sealed and gasketed air cleaners with system efficiencies of HEPA
performance are recommended.
- Benefits:
-
Unlike other filter media that becomes less efficient with
use, HEPA filter media becomes
more efficient with use and will trap smaller and more particles as the
filter captures more and more particles that fill up the
microscopic spaces on the filter fabric.
-
HEPA filtration will remove
particles smaller than 0.3 microns at up to 99% efficiency.
Combined with high air flow rates, a high performance HEPA
air cleaning system has been shown to capture more
sub-micron particles such as viruses, bacteria, allergen and
tobacco smoke than any other air cleaning technology.
-
Many air cleaners claim to
destroy microorganisms, but have never compared themselves
directly with HEPA technology. HEPA filtration will not
re-release trapped particles back into the air.
Microorganisms require a food source and moisture to survive
and many microorganisms have limited lifespans. HEPA filters
do not provide a food source or moisture for microorganisms
to continue to live and therefore they will be killed off
while trapped in a HEPA performance air cleaner.
- Ozonation
- Some air
cleaning units produce
ozone,
a molecule with three atoms of oxygen, either directly or as a by product of
ionization and electrical precipitation. High voltage causes the
oxygen molecules in the air to create ozone (O3).
Ozone does not trap particles, but is claimed to remove odors in the air. Manufacturers of air
cleaner systems that produce ozone may refer to the ozone as "Supercharged Oxygen",
"Activated Oxygen" or "Enhanced Oxygen" and
that they produce clean air in a similar way to a lightning
storm. Other claims of producing only good ozone vs. bad
ozone in the atmosphere are incorrect. All ozone is the same. On the basis that ozone generators produce an indoor pollutant,
there are no safe and acceptable levels of ozone, ozone can
interact with the air to create more indoor pollutants
and ozone does not remove pollutants or particulate matter, these devices are not
recommended.
- Issues:
-
Units that produce ozone only do not
remove particulates from the air. They are not a comprehensive
air cleaning solution.
-
Ozone itself is an
indoor air pollutant and is considered an irritant to
the lungs by many health, state and federal agencies. The American Lung
Association, the US Environmental Protection Agency and the
California Air Resources Board have all publicly condemned the
use of ozone emitting air cleaning devices for use in the home.
-
The Centers for Disease Control in Atlanta, GA states
"Ozone
is an extraordinarily dangerous pollutant....ozone is nearly as effective at
destroying lungs as mustard gas". The US Environmental
Protection Agency (EPA) has stated that ozone is a toxic gas
with vastly different chemical properties than oxygen and when
ozone is inhaled, it can damage the lungs. The EPA further
states that ozone in low amounts can cause chest pain, coughing,
shortness of breath and throat irritation.
-
Scientific evidence
demonstrates that ozone released into the air at concentrations
that do not exceed public health standards, will not effectively
remove viruses, bacteria, molds and many odor-causing chemicals
and is therefore generally ineffective in controlling indoor air
pollution. Ozone deadens the sense of smell making it difficult
to detect odors.
-
Most of these units
can not adjust the production of ozone they produce and many
factors affect ozone concentrations in a room such as the room
size, materials in the room that react with the ozone and the
amount of ventilation. Even when using these devices as
directed, you do not know if you creating a dangerously high
amount of this pollutant in your indoor environment. Generally,
an ozone generator will create ozone levels in a home that
exceed a Stage 1 Smog alert standard for outside air quality.
-
Ozone emitted indoors can lead to
significant increases in indoor levels of other pollutants such
as formaldehyde (a suspected carcinogen), other aldehydes,
V.O.C.'s an ultrafine particulate matter.
-
Photocatalysis
- Used primarily
for the removal of gaseous contaminants, this is a process of
shining ultraviolet light (UV) onto a catalytic surface composed
of a titanium oxide (TiO2) surface coating, to create a
chemical reaction that converts gases that pass through the
device into less harmful substances such as carbon dioxide and
water. Claims of odor removal and germicidal properties are also
made for this technology. This technology has not been tested in
a working device under real living conditions to adequately
prove its effectiveness. This method of chemical control is
not recommended.
- Issues:
-
Units that utilize photocatalysis
may produce ozone.
-
Test reports on the technology to
reduce V.O.C.'s, utilize a testing chamber with 0.2 cfm air flow
rate and contact time of 10 seconds. Testing chamber was 0.14
cubic feet in size. Test conditions demonstrated a 2 - 40
minutes timeframe to reduce contaminant levels by 50%. Available
products using photocatalysis technology use a fan that moves
air over a catalyst coated light tube. The device would produce
significant air flow (50-150cfm?), much shorter contact times
and be located in a room of significantly larger volume (over
1,000 cubic feet). Additionally, it is unknown at what distance
the gas has to be from the light tube to be affected by the photocatalytic reaction. The actual use of these devices in real
life scenarios are substantially different than the test
conditions and makes the application's claimed effectiveness
at microbial, gas and odor control questionable.
-
Testing for bacterial destruction
has similar flaws. Testing was performed with an incubated
bacterial membrane exposed to UV-A light to activate the
photocatalyst on the membrane for a period of 3-24 minutes. A
real life scenario is a photocatalysis device that is pushing
air across a light source with a contact time of milliseconds.
This does not resemble a similar scenario as the test
environment. Even the manufacture of a photocatalysis device
states "New standard tests are needed that use airborne
microbes to determine the Germicidal Rate for a photo-catalytic
system employing forced air convection. Both airflow and air
recirculation would influence the System Germicidal Rate."
- Adsorption
- This is the
physical process of binding gas molecules to a large surface or
pores of an adsorbent medium. Activated carbon is the most
common media used for adsorption and is produced by heating
carbonaceous substances (containing carbon and derived from
organic substances such as bituminous coal, wood or coconut
shell) to form a carbonized char, then activating (oxidizing)
with gases such as steam and carbon dioxide to form pores and
creating a highly porous adsorbent material. Zeolites are
another type of adsorbent and are a class of
naturally occurring minerals derived from volcanic ash. Zeolites can also be
reproduced synthetically because of their consistent and
predictable porous structure. Adsorption technology is
recommended for gas and odor control.
The effectiveness of odor
removing media is related
to the amount and type of gasses present in the air, the
quantity, type and
depth
of the adsorbent material and the velocity of the air traveling through the
media. The location of the odor adsorbing media relative to the particle
filtration media is also important. If the odor adsorbing media is placed
first, then particles in the air will cover the porous structure of the odor
adsorbing media and reduce its effectiveness at trapping odors. By placing
the high efficiency particle filter media first, particles in the air are captured before
the air reaches the odor adsorbing media and allows the porous structure
of the odor adsorbing media to have maximum effectiveness at capturing
gasses. Air cleaning devices with carbon
powder impregnated on mesh filters do not have the depth and quantity of
gas adsorbing media to provide significant odor removing performance for a substantial time period. Room
conditions such as air temperature and humidity also effect the capacity
of adsorbents to remove odors.
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Activated Carbon Pellets |
Close-Up of Activated Carbon
Pores |
- Benefits:
-
Activated carbon has incredible porosity and a large and a
highly active surface area. One pound of activated carbon
has the surface area equal to 125 acres.
Activated carbon is best suited to
remove compounds with high molecular weight such as volatile
organic compounds (V.O.C.'s) like
benzene, toulene and xylene.
-
One pound of Zeolite can have
20 to 30 acres
of surface area. These minerals are effective at removing V.O.C.'s and
ammonia compound odors such as pet odors from urine. Like carbon, gasses are
trapped in the voids of the porous Zeolite structure.
-
Chemisorption
- Chemisorbents work through
a two step process, first physically binding gasses to a carrier
media then, through an oxidative process, the trapped gas
molecules are chemically broken down. The common carrier media
is activated alumina, which is made by treating aluminum ore so
it becomes porous and highly adsorptive. Another carrier media
for chemisorption is activated carbon. A binder such as
activated alumina is impregnated with Potassium Permanganate to
create a chemically active media. Potassium Permanganate is a
dark purple substance that is a powerful oxidizing agent. Use of
chemisorption for gas and odor control is recommended.
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Pelletized
Activated Carbon and Activated Alumina with Potassium
Permanganate |
- Benefits:
-
These odor control
substances are best for the removal of high molecular weight gasses such as
formaldehyde, ammonia and hydrogen sulfide.
-
This non-toxic media first physically traps selected gas
molecules and then chemically destroys them through a
process called oxidation. This oxidation process is media
based and no oxygen or ozone is generated.
-
Since there is a chemical
process involved to break down the odor and gasses, there is
no re-emission possible for the gaseous pollutants.
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