Ozone Generators that are Sold as Air Cleaners: An Assessment of
Effectiveness and Health Consequences
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.
Please Note: EPA does not certify air cleaning devices. The Agency does not recommend air cleaning
devices or manufacturers. If you need information on specific 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 www.aham.org. AHAM also provides information on
air cleaners on their AHAM-certified Clean Air Delivery Rate site at www.cadr.org. Also, the American
Lung Association has an Air Cleaning Device fact sheet at: wywjunigusajjjg^
There are other resources provided in this fact sheet. For more information on Indoor Air Quality, please
see hjtp;//www1ep_ag_oy/[ag
Contents
What is ozone?
How is ozone harmfu!?
- Ozone Heath Effects and Standards
^
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?
Conclusions
Recommendation
Additional Resources
- Publjcatjgns
- Inforrnatjon Sgurces
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; Sails, 1927; Boeniger, 1995; American
Lung Association, 1997; AI-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.
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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.
What is Ozone?
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.
How is Ozone Harmful?
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
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.,
The Food an d D ru g Ad m i n i strati on (FDA)
requires ozone output of indoor medical devices to
be no more than 0.05 ppm.
The Qccupational Safety and HeaIth
Administration (OSHA) requires that workers not
be exposed to an average concentration of more
than 0.10 ppm for S 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
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Inflammation of lung
tissue
Higher susceptibility to
respiratory infection
exercise)
Certain pre-existing lung
diseases (e.g., asthma)
National Ambient Air Quality Standard for ozone is
a maximum 8 hour average outdoor concentration
of 0.08 ppm.
(* ppm = parts per million)
Is There Such a Thing as "Good Ozone" and "Bad Ozone"?
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.
Are Ozone Generators Effective in Controlling Indoor Air Pollution?
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 (Sails, 1927; Shaughnessy etal., 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.
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• 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.
If I Follow Manufacturers' Directions, Can I be Harmed?
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.
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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 (see Table 1).
• 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.
Why is it Difficult to Control Ozone Exposure with an Ozone Generator?
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
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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.
Can Ozone be Used in Unoccupied Spaces?
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).
What Other Methods Can Be Used to Control Indoor Air Pollution?
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.
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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.
Conclusions
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.
Recommendation
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.
Additional Resources
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 -800-490-91987(513) 489-8695 (fax), or write to:
U.S. Environmental Protection Agency
National Center for Environmental Publications (NSCEP)
P.O. Box42419
Cincinnati, OH 45242
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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[Aii-Facts•J^o^J^_Residenti^j^Qeaners,_ EPA Document Number EPA 20A-4-001. U.S. EPA.
February 1990.
Residential ^ EPA Document Number EPA
402-K-96-001. U.S. EPA.
jndoorAir Pgllut^^ 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. http://www.hc-
sc.gc.ca/e^^
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.
FederaTTrade.Commission, Consumer Response Center, (202) 326-3128.
y,S.,.ConsumerProduct; 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 (www. cadr. grg)
Association of Home Appliance Manufacturers (AHAM)
1111 19th Street, NW, Suite 402
Washington, DC 20036
(202) 872-5955
www,_ah_am,_org
AHAM also provides information on air cleaners on their AHAM-certified Clean Air Delivery Rate site at
www^adrorg
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American Lung Association Fact Sheet - Air Cleaining Devices: Types of Air Cleaning Processes
Bibliography
AI-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.
Sails, 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.
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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.
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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
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(703) 356-4020 or 800-438-4318
fax: (703) 356-5386 or e-mail: ia_ginfg@_aQLcQm
or, you can order publications directly via EPA's National Service Center for Environmental
Publications (NSCEP) (MtPi//wvw,_epj_,gQy/nceMhQm/L 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. Box42419
Cincinnati, OH 42419
1-800-490-91987(513) 489-8695 (fax)
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