|
Note:
There is a large body of written material on ozone and the use of
ozone indoors. However, much of this material makes claims or
draws conclusions without substantiation and sound science. In
developing Ozone Generators that are Sold as Air Cleaners,
the EPA reviewed a wide assortment of this literature, including
information provided by a leading manufacturer of ozone generating
devices. In keeping with EPA's policy of insuring that the
information it provides is based on sound science, only peer
reviewed, scientifically supported findings and conclusions were
relied upon in developing this document.
EPA does not certify air cleaning devices, nor recommend air
cleaning devices or manufacturers. One resource you can consult
is the Association of Home Appliance Manufacturers (AHAM) 1111
19th Street, NW, Suite 402, Washington, DC 20036 (202)
872-5955. AHAM also provides information on air cleaners on their
AHAM-certified Clean Air Delivery Rate site at
http://www.cadr.org/ Also, the American Lung Association
has an Air Cleaning Device fact sheet at:
www.lungusa.org/air/air00_aircleaners.html There are
other resources provided in this fact sheet. |
What is ozone?
How is ozone harmful?
- Ozone Heath Effects and Standards
Is there such a
thing as "good ozone," and "bad ozone"?
Are
ozone generators effective in controlling indoor air pollution?
If I follow
manufacturers' directions, can I be harmed?
Why is it difficult to control ozone exposure with an ozone generator?
Can ozone be used in
unoccupied spaces?
What other methods can be used to control indoor air pollution?
Conclusions
Recommendation
Additional Resources
- Publications
- Information Sources
Bibliography
Introduction and Purpose
Ozone generators that are sold as air cleaners intentionally produce
the gas ozone. Often the vendors of ozone generators make statements and
distribute material that lead the public to believe that these devices
are always safe and effective in controlling indoor air pollution. For
almost a century, health professionals have refuted these claims
(Sawyer, et. al 1913; Salls, 1927; Boeniger, 1995; American Lung
Association, 1997; Al-Ahmady, 1997). The purpose of this document is to
provide accurate information regarding the use of ozone-generating
devices in indoor occupied spaces. This information is based on the most
credible scientific evidence currently available.
Some vendors suggest that these devices have been approved by the
federal government for use in occupied spaces. To the contrary, NO
agency of the federal government has approved these devices for use in
occupied spaces. Because of these claims, and because ozone can cause
health problems at high concentrations, several federal government
agencies have worked in consultation with the U.S. Environmental
Protection Agency to produce this public information document.
Ozone is a molecule composed of three atoms of oxygen. Two atoms of
oxygen form the basic oxygen molecule--the oxygen we breathe that is
essential to life. The third oxygen atom can detach from the ozone
molecule, and re-attach to molecules of other substances, thereby
altering their chemical composition. It is this ability to react with
other substances that forms the basis of manufacturers’ claims.
The same chemical properties that allow high concentrations of ozone
to react with organic material outside the body give it the ability to
react with similar organic material that makes up the body, and
potentially cause harmful health consequences. When inhaled, ozone can
damage the lungs. Relatively low amounts can cause chest pain, coughing,
shortness of breath, and, throat irritation. Ozone may also worsen
chronic respiratory diseases such as asthma and compromise the ability
of the body to fight respiratory infections. People vary widely in their
susceptibility to ozone. Healthy people, as well as those with
respiratory difficulty, can experience breathing problems when exposed
to ozone. Exercise during exposure to ozone causes a greater amount of
ozone to be inhaled, and increases the risk of harmful respiratory
effects. Recovery from the harmful effects can occur following
short-term exposure to low levels of ozone, but health effects may
become more damaging and recovery less certain at higher levels or from
longer exposures (US EPA, 1996a, 1996b).
Manufacturers and vendors of ozone devices often use misleading terms
to describe ozone. Terms such as "energized oxygen" or "pure air"
suggest that ozone is a healthy kind of oxygen. Ozone is a toxic gas
with vastly different chemical and toxicological properties from oxygen.
Several federal agencies have established health standards or
recommendations to limit human exposure to ozone. These exposure limits
are summarized in Table 1.
|
Table 1. Ozone Heath Effects and
Standards |
|
Health Effects |
Risk Factors |
Health Standards* |
|
Potential risk of experiencing:
Decreases in lung function
Aggravation of asthma
Throat irritation and cough
Chest pain and shortness of breath
Inflammation of lung tissue
Higher susceptibility to respiratory infection |
Factors expected to
increase risk and severity of health effects are:
Increase in ozone air concentration
Greater duration of exposure for some health effects
Activities that raise the breathing rate (e.g., exercise)
Certain pre-existing lung diseases (e.g., asthma)
|
The
Food and Drug Administration (FDA) requires ozone
output of indoor medical devices to be no more than 0.05 ppm.
The Occupational Safety and Health Administration (OSHA)
requires that workers not be exposed to an average concentration
of more than 0.10 ppm for 8 hours.
The National Institute of Occupational Safety and Health
(NIOSH) recommends an upper limit of 0.10 ppm, not to be exceeded
at any time.
The Environmental Protection Agency (EPA)’s National
Ambient Air Quality Standard for ozone is a maximum 8 hour average
outdoor concentration of 0.08 ppm.
|
|
(* ppm = parts per million) |
The phrase "good up high - bad nearby" has been used by
the U.S. Environmental Protection Agency (EPA) to make the distinction
between ozone in the upper and lower atmosphere. Ozone in the upper
atmosphere--referred to as "stratospheric ozone"--helps filter out
damaging ultraviolet radiation from the sun. Though ozone in the
stratosphere is protective, ozone in the atmosphere - which is the air
we breathe - can be harmful to the respiratory system. Harmful levels of
ozone can be produced by the interaction of sunlight with certain
chemicals emitted to the environment (e.g., automobile emissions and
chemical emissions of industrial plants). These harmful concentrations
of ozone in the atmosphere are often accompanied by high concentrations
of other pollutants, including nitrogen dioxide, fine particles, and
hydrocarbons. Whether pure or mixed with other chemicals, ozone
can be harmful to health.
Available scientific evidence shows that at
concentrations that do not exceed public health standards, ozone has
little potential to remove indoor air contaminants.
Some manufacturers or vendors suggest that ozone will
render almost every chemical contaminant harmless by producing a
chemical reaction whose only by-products are carbon dioxide, oxygen and
water. This is misleading.
-
First, a review of scientific research shows that, for many of the
chemicals commonly found in indoor environments, the reaction process
with ozone may take months or years (Boeniger, 1995). For all
practical purposes, ozone does not react at all with such chemicals.
And contrary to specific claims by some vendors, ozone generators are
not effective in removing carbon monoxide (Salls, 1927; Shaughnessy et
al., 1994) or formaldehyde (Esswein and Boeniger, 1994).
-
Second, for many of the chemicals with which ozone does readily
react, the reaction can form a variety of harmful or irritating
by-products (Weschler et al., 1992a, 1992b, 1996; Zhang and Lioy,
1994). For example, in a laboratory experiment that mixed ozone with
chemicals from new carpet, ozone reduced many of these chemicals,
including those which can produce new carpet odor. However, in the
process, the reaction produced a variety of aldehydes, and the total
concentration of organic chemicals in the air increased rather than
decreased after the introduction of ozone (Weschler, et. al., 1992b).
In addition to aldehydes, ozone may also increase indoor
concentrations of formic acid (Zhang and Lioy, 1994), both of which
can irritate the lungs if produced in sufficient amounts. Some of the
potential by-products produced by ozone’s reactions with other
chemicals are themselves very reactive and capable of producing
irritating and corrosive by-products (Weschler and Shields, 1996,
1997a, 1997b). Given the complexity of the chemical reactions that
occur, additional research is needed to more completely understand the
complex interactions of indoor chemicals in the presence of ozone.
-
Third, ozone does not remove particles (e.g., dust and pollen)
from the air, including the particles that cause most allergies.
However, some ozone generators are manufactured with an "ion
generator" or "ionizer" in the same unit. An ionizer is a device that
disperses negatively (and/or positively) charged ions into the air.
These ions attach to particles in the air giving them a negative (or
positive) charge so that the particles may attach to nearby surfaces
such as walls or furniture, or attach to one another and settle out of
the air. In recent experiments, ionizers were found to be less
effective in removing particles of dust, tobacco smoke, pollen or
fungal spores than either high efficiency particle filters or
electrostatic precipitators. (Shaughnessy et al., 1994; Pierce, et
al., 1996). However, it is apparent from other experiments that the
effectiveness of particle air cleaners, including electrostatic
precipitators, ion generators, or pleated filters varies widely (U.S.
EPA, 1995).
There is evidence to show that at concentrations
that do not exceed public health standards, ozone is not effective at
removing many odor-causing chemicals.
-
In an experiment designed to produce formaldehyde concentrations
representative of an embalming studio, where formaldehyde is the main
odor producer, ozone showed no effect in reducing formaldehyde
concentration (Esswein and Boeniger, 1994). Other experiments suggest
that body odor may be masked by the smell of ozone but is not removed
by ozone (Witheridge and Yaglou, 1939). Ozone is not considered useful
for odor removal in building ventilation systems (ASHRAE, 1989).
-
While there are few scientific studies to support the claim that
ozone effectively removes odors, it is plausible that some odorous
chemicals will react with ozone. For example, in some experiments,
ozone appeared to react readily with certain chemicals, including some
chemicals that contribute to the smell of new carpet (Weschler, 1992b;
Zhang and Lioy, 1994). Ozone is also believed to react with acrolein,
one of the many odorous and irritating chemicals found in secondhand
tobacco smoke (US EPA, 1995).
If used at concentrations that do not exceed
public health standards, ozone applied to indoor air does not
effectively remove viruses, bacteria, mold, or other biological
pollutants.
-
Some data suggest that low levels of ozone may reduce airborne
concentrations and inhibit the growth of some biological organisms
while ozone is present, but ozone concentrations would have to be 5 -
10 times higher than public health standards allow before the ozone
could decontaminate the air sufficiently to prevent survival and
regeneration of the organisms once the ozone is removed (Dyas, et
al.,1983; Foarde et al., 1997).
-
Even at high concentrations, ozone may have no effect on
biological contaminants embedded in porous material such as duct
lining or ceiling tiles (Foarde et al, 1997). In other words, ozone
produced by ozone generators may inhibit the growth of some biological
agents while it is present, but it is unlikely to fully decontaminate
the air unless concentrations are high enough to be a health concern
if people are present. Even with high levels of ozone, contaminants
embedded in porous material may not be affected at all.
Results of some controlled studies show that
concentrations of ozone considerably higher than these standards are
possible even when a user follows the manufacturer’s operating
instructions.
There are many brands and models of ozone generators on
the market. They vary in the amount of ozone they can produce. In many
circumstances, the use of an ozone generator may not result in ozone
concentrations that exceed public health standards. But many factors
affect the indoor concentration of ozone so that under some conditions
ozone concentrations may exceed public health standards.
-
In one study (Shaughnessy and Oatman, 1991), a large ozone
generator recommended by the manufacturer for spaces "up to 3,000
square feet," was placed in a 350 square foot room and run at a high
setting. The ozone in the room quickly reached concentrations that
were exceptionally high--0.50 to 0.80 ppm which is 5-10 times higher
than public health limits.
-
In an EPA study, several different devices were placed in a home
environment, in various rooms, with doors alternately opened and
closed, and with the central ventilation system fan alternately turned
on and off. The results showed that some ozone generators, when run at
a high setting with interior doors closed, would frequently produce
concentrations of 0.20 - 0.30 ppm. A powerful unit set on high with
the interior doors opened achieved values of 0.12 to 0.20 ppm in
adjacent rooms. When units were not run on high, and interior doors
were open, concentrations generally did not exceed public health
standards (US EPA, 1995).
-
The concentrations reported above were adjusted to exclude that
portion of the ozone concentration brought in from the outdoors.
Indoor concentrations of ozone brought in from outside are typically
0.01- 0.02 ppm, but could be as high as 0.03 - 0.05 ppm (Hayes, 1991;
U.S. EPA, 1996b; Weschler et al., 1989, 1996; Zhang and Lioy; 1994).
If the outdoor portion of ozone were included in the indoor
concentrations reported above, the concentrations inside would have
been correspondingly higher, increasing the risk of excessive ozone
exposure.
-
None of the studies reported above involved the simultaneous use
of more than one device. The simultaneous use of multiple devices
increases the total ozone output and therefore greatly increases the
risk of excessive ozone exposure.
The actual concentration of ozone produced by an ozone
generator depends on many factors. Concentrations will be higher if a
more powerful device or more than one device is used, if a device is
placed in a small space rather than a large space, if interior doors are
closed rather than open and, if the room has fewer rather than more
materials and furnishings that adsorb or react with ozone and, provided
that outdoor concentrations of ozone are low, if there is less rather
than more outdoor air ventilation.
The proximity of a person to the ozone generating device
can also affect one’s exposure. The concentration is highest at the
point where the ozone exits from the device, and generally decreases as
one moves further away.
Manufacturers and vendors advise users to size the
device properly to the space or spaces in which it is used.
Unfortunately, some manufacturers’ recommendations about appropriate
sizes for particular spaces have not been sufficiently precise to
guarantee that ozone concentrations will not exceed public health
limits. Further, some literature distributed by vendors suggests that
users err on the side of operating a more powerful machine than would
normally be appropriate for the intended space, the rationale being that
the user may move in the future, or may want to use the machine in a
larger space later on. Using a more powerful machine increases the risk
of excessive ozone exposure.
Ozone generators typically provide a control setting by
which the ozone output can be adjusted. The ozone output of these
devices is usually not proportional to the control setting. That
is, a setting at medium does not necessarily generate an ozone level
that is halfway between the levels at low and high. The relationship
between the control setting and the output varies considerably among
devices, although most appear to elevate the ozone output much more than
one would expect as the control setting is increased from low to high.
In experiments to date, the high setting in some devices generated 10
times the level obtained at the medium setting (US EPA, 1995).
Manufacturer’s instructions on some devices link the control setting to
room size and thus indicate what setting is appropriate for different
room sizes. However, room size is only one factor affecting ozone levels
in the room.
In addition to adjusting the control setting to the size
of the room, users have sometimes been advised to lower the ozone
setting if they can smell the ozone. Unfortunately, the ability to
detect ozone by smell varies considerably from person to person, and
one’s ability to smell ozone rapidly deteriorates in the presence of
ozone. While the smell of ozone may indicate that the concentration is
too high, lack of odor does not guarantee that levels are safe.
At least one manufacturer is offering units with an
ozone sensor that turns the ozone generator on and off with the intent
of maintaining ozone concentrations in the space below health standards.
EPA is currently evaluating the effectiveness and reliability of these
sensors, and plans to conduct further research to improve society’s
understanding of ozone chemistry indoors. EPA will report its findings
as the results of this research become available.
Ozone has been extensively used for water purification,
but ozone chemistry in water is not the same as ozone chemistry in air.
High concentrations of ozone in air, when people are not present,
are sometimes used to help decontaminate an unoccupied space from
certain chemical or biological contaminants or odors (e.g., fire
restoration). However, little is known about the chemical by-products
left behind by these processes (Dunston and Spivak, 1997). While high
concentrations of ozone in air may sometimes be appropriate in these
circumstances, conditions should be sufficiently controlled to
insure that no person or pet becomes exposed. Ozone can
adversely affect indoor plants, and damage materials such as rubber,
electrical wire coatings, and fabrics and art work containing
susceptible dyes and pigments (U.S. EPA, 1996a).
The three most common approaches to reducing indoor air
pollution, in order of effectiveness, are:
-
Source Control: Eliminate or control the sources of
pollution;
-
Ventilation: Dilute and exhaust pollutants through
outdoor air ventilation, and
-
Air Cleaning: Remove pollutants through proven air
cleaning methods.
Of the three, the first approach -- source control -- is the most effective. This involves minimizing the use of
products and materials that cause indoor pollution, employing good
hygiene practices to minimize biological contaminants (including the
control of humidity and moisture, and occasional cleaning and
disinfection of wet or moist surfaces), and using good housekeeping
practices to control particles.
The second approach -- outdoor air ventilation --
is also effective and commonly employed. Ventilation methods include
installing an exhaust fan close to the source of contaminants,
increasing outdoor air flows in mechanical ventilation systems, and
opening windows, especially when pollutant sources are in use.
The third approach -- air cleaning -- is not
generally regarded as sufficient in itself, but is sometimes used to
supplement source control and ventilation. Air filters, electronic
particle air cleaners and ionizers are often used to remove airborne
particles, and gas adsorbing material is sometimes used to remove
gaseous contaminants when source control and ventilation are inadequate.
See Additional Resources section below for more detailed
information about these methods.
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(s), 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.
The public is advised to use proven methods of
controlling indoor air pollution. These methods include
eliminating or controlling pollutant sources, increasing outdoor air
ventilation, and using proven methods of air cleaning.
Publications:
Copies of EPA's publications are available from the
National Service Center for Environmental Publications (NSCEP)
http://www.epa.gov/ncepihom/ (to order EPA documents online). Use the
EPA Document Number when ordering. Or call 1-800-490-9198/(513)
489-8695 (fax), or write to:
U.S. Environmental Protection Agency
National Center for Environmental Publications (NSCEP)
P.O. Box 42419
Cincinnati, OH 45242
The Inside Story: A Guide to Indoor Air
Quality, EPA Document Number EPA 402-K-93-007. U.S. EPA, U.S. CPSC.
April 1995.
Indoor Air Facts No. 7.- Residential Air
Cleaners, EPA Document Number EPA 20A-4-001. U.S. EPA. February
1990.
Residential Air Cleaning Devices: A Summary of
Available Information, EPA Document Number EPA 402-K-96-001.
U.S. EPA.
Indoor Air Pollution: An Introduction for Health
Professionals,
EPA Document Number EPA 402-R-94-007. American Lung Association, EPA,
CPSC, American Medical Association.
Advisory:
"Health Canada Advises the Public About Air Cleaners
Designed to Intentionally Generate Ozone (Ozone Generators)", Health
Canada, Canada 1999-19, February 5, 1999.
Information Sources:
U.S. EPA's Indoor Air Quality Information
Clearinghouse (IAQ INFO), PO Box 37133, Washington D.C. 20013-7133; by
phone (800) 438-4318.
California Department of Health Services, Indoor Air
Quality Section, Environmental Health Laboratory, 2151 Berkeley Way,
Berkeley, CA 94704; 510-540-3022.
Federal Trade Commission , Consumer Response Center,
(202) 326-3128.
U.S. Consumer Product Safety Commission,
Washington D.C. 20207; or call Consumer Hotline, English/Spanish:
(800) 638-2772, Hearing/Speech Impaired: (800) 6388270.
The Association of Home Appliance Manufacturers (AHAM) has
developed an American National Standards Institute (ANSI)-approved
standard for portable air cleaners (ANSI/AHAM Standard AC-1-1988).
This standard may be useful in estimating the effectiveness of
portable air cleaners. Under this standard, room air cleaner
effectiveness is rated by a clean air delivery rate (CADR) for each of
three particle types in indoor air: tobacco smoke, dust, and pollen.
Only a limited number of air cleaners have been certified under
this program at the present time. A complete listing of all current
AHAM-certified room air cleaners and their CADRs can be obtained from
CADR .
Association of Home Appliance Manufacturers (AHAM)
1111 19th Street, NW, Suite 402
Washington, DC 20036
(202) 872-5955
AHAM also provides information on air cleaners on their AHAM-certified
Clean Air Delivery Rate site at http://www.cadr.org/
American Lung Association Fact Sheet - http://www.lungusa.org/
Al-Ahmady, Kaiss K. 1997. Indoor Ozone. Florida
Journal of Environmental Health. June. pp. 8-12.
American Lung Association. 1997. Residential Air
Cleaning Devices: Types, Effectiveness, and Health Impact. Washington,
D.C. January.
American Society of Heating, Refrigerating, and Air
Conditioning Engineers (ASHRAE). 1989. ASHRAE Handbook of
Fundamentals. Atlanta. p. 12.5.
Boeniger, Mark F. 1995. Use of Ozone Generating Devices
to Improve Indoor Air Quality. American Industrial Hygiene
Association Journal. 56: 590-598.
Dunston, N.C.; Spivak, S.M. 1997. A Preliminary
Investigation of the Effects of Ozone on Post-Fire Volatile Organic
Compounds. Journal of Applied Fire Science. 6(3): 231-242.
Dyas, A.; Boughton, B.J.; Das, B.C. 1983. Ozone Killing
Action Against Bacterial and Fungal Species; Microbiological Testing of
a Domestic Ozone Generator. Journal of Clinical Pathology.
36:1102-1104.
Esswein, Eric J.; Boeniger, Mark F. 1994. Effects of an
Ozone-Generating Air-Purifying Device on Reducing Concentrations of
Formaldehyde in Air. Applied Occupational Environmental Hygiene.
9(2):139-146.
Foarde, K.; van Osdell, D.; and Steiber, R.1997.
Investigation of Gas-Phase Ozone as a Potential Biocide. Applied
Occupational Environmental Hygiene. 12(8): 535-542.
Hayes, S.R. 1991. Use of an Indoor Air Quality Model (IAQM)
to Estimate Indoor Ozone Levels. Journal of Air and Waste Management
Association. 41:161-170.
Pierce, Mark W.; Janczewski, Jolanda N.; Roethlisbergber,
Brian; Pelton, Mike; and Kunstel, Kristen. 1996. Effectiveness of
Auxiliary Air Cleaners in Reducing ETS Components in Offices. ASHRAE
Journal. November.
Salls, Carroll, M. 1927. The Ozone Fallacy in Garage
Ventilation. The Journal of Industrial Hygiene. 9:12. December.
Sawyer, W.A.; Beckwith, Helen I.; and Skolfield, Esther
M. 1913. The Alleged Purification of Air By The Ozone Machine.
Journal of the American Medical Association. November 13.
Shaughnessy, Richard, J.; Levetin, Estelle; Blocker,
Jean; and Sublette, Kerry L. 1994. Effectiveness of Portable Indoor Air
Cleaners: Sensory Testing Results. Indoor Air. Journal of the
International Society of Indoor Air Quality and Climate.
4:179-188.
Shaughnessy, R.J.; and Oatman, L. 1991. The Use of Ozone
Generators for the Control of Indoor Air Contaminants in an Occupied
Environment. Proceedings of the ASHRAE Conference IAQ ‘91. Healthy
Buildings. ASHRAE, Atlanta.
U.S. Environmental Protection Agency (US EPA). 1995.
Ozone Generators in Indoor Air Settings. Report prepared for the Office
of Research and Development by Raymond Steiber. National Risk Management
Research Laboratory. U.S. EPA. Research Triangle Park. EPA-600/R-95-154.
U.S. Environmental Protection Agency (US EPA). 1996. Air
Quality Criteria for Ozone and Related Photochemical Oxidants. Research
Triangle Park, NC: National Center for Environmental Assessment-RTP
Office; report nos. EPA/600/P-93/004aF-cF, 3v. NTIS, Springfield, VA;
PB-185582, PB96-185590 and PB96-185608.
U.S. Environmental Protection Agency (US EPA). 1996.
Review of National Ambient Air Quality Standards for Ozone: Assessment
of Scientific and Technical Information. OAQPS Staff Paper. Office of
Air Quality Planning and Standards. Research Triangle Park. NC.
EPA-452/R-96-007.
Weschler, Charles J.; Brauer, Michael; and Koutrakis,
Petros. 1992a. Indoor Ozone and Nitrogen Dioxide: A Potential Pathway to
the Generation of Nitrate Radicals, Dinitrogen Pentaoxide, and Nitric
Acid Indoors. Environmental Science and Technology.
26(1):179-184.
Weschler, Charles J.; Hodgson Alfred T.; and Wooley,
John D. 1992b. Indoor Chemistry: Ozone, Volatile Organic Compounds, and
Carpets. Environmental Science and Technology. 26(12):2371-2377.
Weschler, Charles J; Shields, Helen C. 1997a.
Measurements of the Hydroxyl Radical in a Manipulated but Realistic
Indoor Environment. Environmental Science and Technology.
31(12):3719-3722.
Weschler, Charles J; Shields, Helen C. 1997b. Potential
Reactions Among Indoor Pollutants. Atmospheric Environment.
31(21):3487-3495.
Weschler, Charles J; and Shields, Helen C. 1996.
Production of the Hydroxyl Radical in Indoor Air. Environmental
Science and Technology. 30(11):3250-3268.
Weschler, Charles J.; Shields, Helen, C.; and Naik,
Datta V. 1989. Indoor Ozone Exposures. JAPCA Journal.
39(12):1562-1568.
Weschler, Charles J.; Shields, Helen, C.; and Naik,
Datta V. 1996. The Factors Influencing Indoor Ozone Levels at a
Commercial Building in Southern California: More that a Year of
Continuous Observations. Tropospheric Ozone. Air and Waste
Management Association. Pittsburgh.
Witheridge, William N. And Yaglou, Constantin P. 1939.
Ozone in Ventilation--Its possibilities and Limitations. ASHRAE
Transactions. 45: 509-522.
Zhang, Junfeng and Lioy, Paul J. 1994. Ozone in
Residential Air: Concentrations, I/O Ratios, Indoor Chemistry, and
Exposures. Indoor Air. Journal of the International Society of
Indoor Air Quality and Climate. 4:95-102.
To order any of our indoor air publications, contact:
IAQ INFO Clearinghouse
PO Box 37133
Washington D.C. 20013-7133
(703) 356-4020 or 800-438-4318
fax: (703) 356-5386 or e-mail:
iaqinfo@aol.com
or, you can order publications directly via EPA's National
Service Center for Environmental Publications (NSCEP) (http://www.epa.gov/ncepihom/
web site. Your publication requests can also be mailed, called or
faxed directly to:
U.S. Environmental Protection Agency
National Center for Environmental Publications (NSCEP)
P.O. Box 42419
Cincinnati, OH 42419
1-800-490-9198/(513) 489-8695 (fax)
For Additional Information on Ozone
|
