Do Air Purifiers Really Work?
The typical furnace filter installed in the ductwork of most
home heating and/or air-conditioning systems is a simple air cleaner. This
basic filtering system may be upgraded by using another filter to trap
additional pollutants or by adding additional air-cleaning devices. An
alternative to upgrading the induct air cleaning system is using individual
room, portable air cleaners. Air cleaners generally rely on filtration, or the
attraction of charged particles to the air cleaning device itself or to
surfaces within the home, for the removal of pollutants. The use of "air
cleaning" to remove pollutants from the air in residences is in its
infancy.
Because many factors need to be considered in determining
whether use of an air cleaner is appropriate in a particular setting, the
decision whether or not to use an air cleaner is left to the individual. As of
yet, the U.S. Environmental Protection Agency has not taken a position either
for or against the use of these devices in the home.
Three Strategies (in order of effectiveness) May Be Used to Reduce Indoor
Air Pollutants:
1. Source Control eliminates individual sources of
pollutants or reduces their emissions, and is generally the most effective
strategy. Some sources, like those that contain asbestos, can be sealed or
enclosed; others, like combustion appliances, can be adjusted to decrease the
amount of emissions. Unfortunately, not all pollutant sources can be identified
and practically eliminated or reduced.
2. Ventilation brings outside air indoors. It can be
achieved by opening windows and doors, by turning on local bathroom or kitchen
exhaust fans, or, in some situations, by the use of mechanical ventilation
systems. However, there are practical limits to the extent ventilation can be
used to reduce airborne pollutants. Costs for heating or cooling incoming air
can be significant, and outdoor air itself may contain undesirable levels of
contaminants.
3. Air Cleaning may serve as an adjunct to source control
and ventilation. However, the use of air cleaning devices alone cannot assure
adequate air quality, particularly where significant sources are present and
ventilation is inadequate. Air cleaners are usually classified by the method
employed for removing particles of various sizes from the air.
There are three general types of air cleaners on the market:
mechanical filters, electronic air cleaners, and ion generators. Air cleaners
may be in-duct units (installed in the central heating and/or air-conditioning
system) or stand-alone portable units.
The effectiveness of air cleaners in removing pollutants
from the air is a function of both the efficiency of the device itself and the
amount of air handled by the device. A product of these two factors (for a
given pollutant) is expressed as the unit's clean air delivery rate (CADR).
Portable air cleaners vary in size and effectiveness in
pollutant reduction capabilities. They range from relatively ineffective
table-top units to larger, more powerful console units. In general, units
containing either electrostatic precipitators, negative ion generators, or
pleated filters, and hybrid units containing combinations of these mechanisms,
are more effective than flat filter units in removing tobacco smoke particles.
Effectiveness within these classes varies widely, however. For removal of
larger dust particles, negative ion generators, without additional particle
capture mechanisms (e.g., filters), may perform poorly.
Pollutants in indoor air may be divided into three groups:
particles, gaseous pollutants, and radon. Some air cleaners, under the right
conditions, can effectively remove small particles which are suspended in air.
However, controversy exists as to the efficiency of air cleaners in removing
larger particles such as pollen and house dust allergens, which rapidly settle
on surfaces. Animal dander may settle more slowly, although the surface
particles far exceed the amount in the air. Therefore, control of the sources
of allergens and ventilation should be stressed as the primary means of
reducing allergic reactions.
Some of the air cleaners containing sorbents may also remove
some of the gaseous pollutants in indoor air. However, no air-cleaning systems
are expected to totally eliminate all hazards from gaseous pollutants and these
systems may have a limited lifetime before replacement is necessary. In
addition, air cleaning may not be effective in reducing the risks of lung
cancer due to radon.
What to look for when choosing an air cleaner:
- The potential effectiveness of the device under the conditions it will be used.
- The need for routine maintenance, including cleaning and replacement of filters.
- The estimated capital and maintenance cost.
- The installation requirements (e.g., power, access).
- The manufacturer's recommended operating procedures.
- The possible production or re-dispersal of pollutants, such as ozone, particles, formaldehyde and trapped gaseous pollutants.
- The inability of some air cleaners to control gases and some odors, such as those from tobacco smoke.
- Possible health effects from charged particles produced by ion generators.
- Possible soiling of surfaces by charged particles produced by ion generators.
- The noise level at the air flow rates that will be used.
Are Ozone Generators Effective?
Available scientific evidence shows that at concentrations
that do not exceed public health standards, ozone has little potential to
remove indoor air contaminants.
Whether in its pure form or mixed with other chemicals,
ozone can be harmful to health. When inhaled, ozone can damage the lungs.
Relatively low amounts of ozone can cause chest pain, coughing, shortness of
breath and throat irritation.
It may also worsen chronic respiratory diseases such as
asthma as well as compromise the ability of the body to fight respiratory
infections.
Some studies show that ozone concentrations produced by
ozone generators can exceed health standards even when one follows
manufacturer's instructions. Many factors affect ozone concentrations including
the amount of ozone produced by the machine, the size of the indoor space, the
amount of material in the room with which ozone reacts, the outdoor ozone
concentration, and the amount of ventilation. These factors make it difficult
to control the ozone concentration in all circumstances.
Available scientific evidence shows that, at concentrations
that do not exceed public health standards, ozone is generally ineffective in
controlling indoor air pollution. The concentration of ozone would have to
greatly exceed health standards to be effective in removing most indoor air
contaminants. In the process of reacting with chemicals indoors, ozone can
produce other chemicals that themselves can be irritating and corrosive.
