EPA-600/R-95-154
October 1995
OZONE GENERATORS
IN INDOOR AIR SETTINGS
Raymond S. Steiber
National Risk Management Research Laboratory
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711
Prepared for:
U. S. Environmental Protection Agency
Office of Research and Development
Washington, DC 20460
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TECHNICAL REPORT DATA
(PhnenadliumittioittoitthemeTtebeforecomf
1. REPORT NO.
EPA-600/R-95-154
PB96-100201
4. TITLE AND SUBTITLE
Ozone Generators in Indoor Air Settings
9. PERFORMING ORGANIZATION CODE
7. AUTHORISF
Raymond S. Steiber
B. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING OROANIZATION NAME AND ADDRESS
10, PROGRAM ELEMENT NO.
See Block 12
11. CONTRACT/GRANT NOT
NA (Inhouse)
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
13. TYPE Of REPORT AND PERIOD COVERED
Final; 6/92 - 12/93
14. SPONSORING AGENCY CODE
EPA/600 A3
i».SUPPLEMENTARY NOTES Author Steiber's mail drop is 54; his phone number is 919/541-
2288. (.
i«. ABSTRACT
report gives information on home/office ozone generators. It discusses
their current uses as amelioratives for environmental tobacco smoke, biocontami-
nants, volatile organic compounds, and odors, and details the advantages and disad-
vantages of- each. Ozone appears to work well against household odors and environ-
mental tobacco smoke, but caution needs to be exercised in its use because of the
production of byproducts such as formaldehyde. Ozone has biocidal effects, but its
use in household settings is limited by the high concentrations needed for complete
kills. Ozone has decremental effects on lung function in humans that persist for 24-
28 hours. In the experiments conducted at the indoor air test house, each of the three
ozone generators studied produced concentrations in excess of the Occupational Safe-
ty and Health Administration limit for workplace exposures. In addition, when inter-
ior doors were left open, adjoining rooms were also subjected to such exposures.
Total ozone decay times for all the concentrations studied did not exceed 12 minutes.":
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
(•.IDENTIFIERS/OPEN ENDED TERMS
s. COSATI Ffetd/Group
Pollution
Ozone
Generators
Tobacco
Smoke
Contaminants
Volatility
Organic Compounds
Odors
Biocides
Pollution Control
Stationary Sources
Ozone Generators
Biocontaminants
3B 20M
37B 07 C
L4G 06P
36C.02D
21B 21D
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport}
Unclassified
21. NO-OF PAGES
34
20. SECURITY CLASS (TMtptft)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
•' C
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FOREWORD
The U. S. Environmental Protection Agency is charged by Congress with pro*
tec ting the Nation's land, air, and water resources. Under a mandate of national
environmental laws, the Agency strives to formulate and implement actions lead-
ing to a compatible balance between human activities and the ability of natural
systems to support and nurture life. To meet this mandate. EPA's research
program is providing data and technical support for solving environmental pro-
blems today and building a science knowledge base necessary to manage our eco-
logical resources wisely, understand how pollutants affect our health, and pre-
vent or reduce environmental risks in the future.
The National Risk Management Research Laboratory is the Agency's center for
investigation of technological and management approaches for reducing risks
from threats to human health and the environment. The focus of the Laboratory's
research program is on methods for the prevention and control of pollution to air.
land, water, and subsurface resources; protection of water quality in public water
systems; remediation of contaminated sites and groundwater; and prevention and
control of indoor air pollution. The goal of this research effort is to catalyze
development and implementation of innovative, cost-effective environmental
technologies; develop scientific and engineering information needed by EPA to
support regulatory and policy decisions; and provide technical support and infbr-
mation transfer to ensure effective implementation of environmental regulations
and strategies.
This publication has been produced as part of the Laboratory's strategic long-
term research plan. It is published and made available by EPA's Office of Re-
search and Development to assist the user community and to link researchers
with their clients.
E. Timothy Oppelt, Director
National Risk Management Research Laboratory
EPA REVIEW NOTICE
This report has been peer and administratively reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.
This document is available to tha public through the National Technical Information
Service, Springfield, Virginia 22161.
ii
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SUMMARY
This report presents information on home/office ozone
generators. It discusses their current uses as amelioratives for
environmental tobacco smoke (ETS), biocontaminants, volatile
organic compounds, and odors and details the advantages and
disadvantages of each. Ozone appears to work well against
household odors and ETS, but caution needs to be exercised in its
use because of the production of byproducts such as formaldehyde.
Ozone has biocidal effects, but its use in household settings is
limited by the high concentrations needed for complete kills.
Ozone has decremental effects on lung function in humans that
persist for 24-48 hours.
In experiments conducted at the indoor air test house, each of
the three ozone generators studied produced concentretions in
excess of the Occupational Safety and Health Administration limit
for workplace exposures. In addition, when interior doors were
left open, adjoining rooms were also subjected to such exposures.
Total ozone decay times for all the concentrations studied did not
exceed 12 minutes.
iii
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CONTENTS
Page
SUMMARY HI
TABLES
FIGURES
CHAPTER 1: OZONE AS AN INDOOR AIR AMELIORATIVE 1
Ozone Chemistry 2
Ozone and Formaldehyde 3
Odor Control 6
Ozone as a Biocide 7
Health Effects 9
Summary 10
CHAPTER 2: TEST HOUSE STUDIES OF OZONE GENERATORS 11
Outputs of Three Ozone Generators 11
Ozone Transport 17
Ozone Decay 20
Summary 24
REFERENCES 25
APPENDIX: Quality Assurance Statement 27
IV
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TABLES
Ho. Title Page
1 Ozone Generator Outputs at the Face in Milligrams/Hour...13
2 Unit A: Maximum Sustainable Ozone Concentrations 15
3 Unit B: Maximum Sustainable Ozone Concentrations... 15
4 Unit C: Maximum Sustainable Ozone Concentrations 16
5 Transport Tests, Group 1 18
6 Ozone Transport, HVAC Off 19
7 Ozone Transport, HVAC On 20
FIGURES
No. Title Page
1 Ultraviolet-initiated ozone reaction chain 4
2 Test house floor plan 12
3 Ozone decay curves: high range 22
4 Ozone decay curves: low range 23
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CHAPTER 1
OZONE AS AN INDOOR AIR AMELIORATIVE
Ozone generators are advertized by their manufacturers as cure-
alls for a large number of indoor air complaints. They are claimed
to be effective at eliminating environmental tobacco smoke (ETS),
biocontaminants such as molds and bacteria, volatile organic
compounds (VOCs), and odors. Such claims are generally accompanied
by customer testimonials that describe the results of using the
generators in glowing terms. These generators can be found in a
wide variety of settings. Hotels and motels use them to get rid of
the odor of stale tobacco smoke and thus provide their guests with
a "smoke-free" environment. Some hotels even mount them
permanently in their rooms, usually hidden behind a grill near the
ceiling. Although individual practices undoubtedly vary, many of
these may be in continuous operation at low settings.
Other venues in which ozone generators are used include
restaurants, offices, bars, and homes. They are used in schools to
deal with molds and bacteria and in nursing homes to eliminate the
odors associated with the illnesses of the aged. And yet, despite
this widespread use and the many claims of effectiveness, there is
little or no supporting data in the scientific literature. This
does not mean that the claims are untrue, but merely that they are
as yet unsubstantiated.
1
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OZONE CHEMISTRY
Ozone (Oj) is produced by either the electrical or ultraviolet
(UV) irradiation of the normal oxygen molecule (02). If nitrogen
is present, the electrical discharge method will co-produce
nitrogen oxides. 03 is a more active oxidant than O2, but this does
not mean that it readily oxidizes every class of organic compound
exposed to it (alkanes, for instance, do not react with ozone at
all) or that the products of such oxidations will be innocuous.
Ozone reacts rapidly with alkenes (olefins) to form aldehydes and
ketones. It also reacts rapidly with alkynes to produce carboxylic
acids. It reacts with water (H20) molecules to form hydrogen
peroxide (H2O2) and with nitrogen oxide (NO) and nitrogen dioxide
(N02) to form N02 and nitrogen pentoxide (N205), respectively. The
process by which ozone reacts with organic compounds is known as
ozonolysis. In the case of alkenes and alkynes, ozone reacts at
the unsaturated carbon:carbon bonds, cleaving the molecule and
forming separate oxygenated byproducts. Except at extreme
concentrations where a continuous chain of reactions might
eventually exhaust the available organic material, leaving behind
carbon dioxide (C02) and water, it is not true that ozonation
destroys volatile organic compounds as a class. Rather it reacts
with them to form new groups of VOCs, some of which may actually be
more toxic1 than the compounds they have replaced. This statement
is substantiated by studies2 of polluted airsheds in which ozone
2
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plays an important role in the formation of the compounds that
constitute smog.
Figure 1 shows a typical UV-initiated ozone reaction chain.
The reactions shown are based on reports3'4 in the literature and do
not/ by any means, constitute the only ones that can occur. In
this case, the chain is started when a normal 02 molecule is
cleaved due to irradiation by ultraviolet light in the 185
nanometer (nm) band. The single oxygen atoms join with other O2
molecules to form 03. Further irradiation in the 254 nanometer
band results in the formation of a highly reactive oxygen singlet
(O*) . This singlet is important in that it reacts with H20 to
produce both hydrogen peroxide and hydroxyl (OH") radicals, both of
which play a role in further reactions (the reaction that produces
N20 is speculation on the part of the author and may not occur in
nature). As can be seen, UV-initiated ozone reactions are complex
and set the stage for later reactions that, far from destroying
VOCs, may result in the formation of more complex organics, some of
which may be nitrated.
OZONE AND FORMALDEHYDE
Formaldehyde is a toxic agent with a Threshold Limit Value
(TLV) of 1 part per million in air. It is also suspected of being
a carcinogen. Formaldehyde is one of a number of aldehydes that
can be formed when ozone reacts at the unsaturated carbon:carbon
3
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O2 -I- photon (185 nm) = 20
O + 02 (+M) s O, (+M)
O3 + photon (254 nm) s O2 + O*
= 2OR
H2O2 + photon (254 nm) c 2OH
OH + RH = R + H20
O 5 -f NO a H02 + 02
OB -f RH w/unsat. C:C bond
= oxygenated R fragments
(RO) (ROH) etc.
O, + RH w/unsat. C:C bond
s oxygenated R fragments
(RO) (ROH) etc.
(esp. when R is an acetyl group)
.and so forth
O* : highly reactive, short-lived oxygen singlet
FIGORB i. Ultraviolet-initiated ozone reaction chain,
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bonds of an olefin. Olefins constitute a significant portion of
the hydrocarbons found in mineral oil, and mineral oil is widely
used as a solvent for binders in home furnishings and building
materials. As a consequence, olefins are ubiquitous in the VOC
background of any office or household. Therefore, it seems likely
that the presence of any amount of ozone within a dwelling, whether
it comes from outside air, electrical appliances, or ozone
generators, will result in the formation of some concentration of
aldehydes.
In a study conducted by Weschler et al.5, carpet was exposed
to parts per billion concentrations of ozone in a stainless steel
chamber. The concentrations of formaldehyde, acetaldehyde, and
aldehydes with higher carbon numbers increased significantly in the
chamber headspace. At the same time there was a corresponding
decrease,, in unsaturated VOC concentrations. In a follow-up study
conducted by Zhang and Lioy6 in six residential houses, formation
of the same series of aldehydes was observed in the presence of
ozone. However, increases in formaldehyde concentrations were
relatively insignificant when compared to those emitted by other
sources in the households (formaldehyde is used in fabrics,
particle board, plywood, and other products). Zhang and Lioy also
observed increases in the presence of formic acid, particularly as
indoor humidity increased.
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ODOR CONTROL
Ozone is documented as being effective in eliminating
unpleasant tastes and odors in drinking water. Persson et al.7
have shown that, at concentrations of 4.0 milligrams/liter, ozone
will remove 80-90% of the geosmin and 2-methyl isoborneol (MIB)
found in the water. These bacterially produced alcohols impart
particularly strong tastes and odors. Ozone is also an effective
oxidant for reduced sulfur compounds, another bad tasting and bad
smelling ingredient of some drinking waters. In addition, ozone
works well against reduced chlorine compounds such as
trihalomethanes.
MIB, geosmin, and reduced sulfur compounds such as dimethyl
disulfide are found in indoor air and account for many of the
household odors associated with biocontamination. They are most
frequently associated with actinomyces, such as streptomyces sp^.
a fungus-like bacterium that is also found in soils. In water,
contact time for the elimination of these chemicals by ozone is 6-
12 minutes, but destruction in household air would probably take
much longer due to greater dilution in the vapor state.
Ozone is claimed to be effective in combatting the odors of
tobacco smoke and is widely used for that purpose with apparent
success. Researchers8 have identified large numbers of separate
compounds as components of ETS. These include nitrosamine,
polynuclear aromatic hydrocarbons, nicotine, phenols, ketones, and
a host of others. In terms of odor, however, the aldehyde
6
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acrolein, C3H40, is probably the most important. Acrolein has a
pungent odor and causes eye and nose irritation. It is acrolein
that leaves a raw, burning flavor in the mouths of heavy smokers.
Acrolein is not very stable, and, although no supporting data
presently exist, one can speculate that it readily reacts with
ozone. If this is indeed the case, it would go far in explaining
ozone's claimed effectiveness as an ameliorative for ETS.
Users of ozone generators frequently comment on the pleasant
odor they leave behind after they have been turned off. Since
ozone rapidly decays to the normal oxygen molecule (10-12 minutes
for most concentrations), this odor is not the ozone itself but
some combination of its most common reaction products. The odor is
frequently described as a "clean sheet" smell or the odor that
clothing gives off when it is fresh out of the drier. The exact
nature of the compounds that cause this odor is not known, but one
can speculate that they may be some combination of hydrogen
peroxide and the oxides of nitrogen. At low concentrations some of
the oxides of nitrogen, particularly nitrous oxide, have a
pleasant, sweetish smell. In addition, they are known to cause
mild feelings of euphoria.
OZONE AS A BIOCIDE
Ozone has been used since 1903 in France and since 1934 in the
U.K. as a biocide in the purification of drinking water. In recent
7
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years, ozone has also been touted as a biocide for molds and
bacteria in the household. The typical ozone generator marketed
for home use develops concentrations of from 0.1 to 0.4 part per
million in the average room. These numbers assume an air exchange
rate with the outside of 0.25 to 0.5 room air exchanges per hour.
Somewhat larger generators are used by commercial duct cleaners,
but even here concentrations seldom exceed 1 to 2 parts per
million. (Some especially large units that are mainly used for
eliminating the odors left behind by building fires are claimed to
operate in the 20 parts per million range.)
Foarde et al.9 conducted chamber experiments in which the
spores of two separate fungi (Penicillium chrysoqenum and
Penicillium glabrum) were exposed to selected concentrations of
ozone for 24 hours at two relative humidities (RHs), 30% and 90%.
In addition, the spores of the spore-forming bacterium Streptomvces
sp. and a living yeast, Rhodotorula glutinis. were exposed in the
same manner. Destruction at such a level as to preclude either
regrowth or survival did not begin to occur until ozone
concentrations had reached the 5-10 parts per million range. The
kill ratios were very much RH dependent, with greater
concentrations of ozone required at the lower RH. When ceiling
tiles were used as a substrate for the deposition of the spores,
kill ratios dropped even lower. Ozone, then, does have biocidal
effects, but for it to be used successfully in household settings,
much higher concentrations must be applied than are now generally
the case. Given the collateral effects, such as damage to rubber
8
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products and the formation of byproducts, it remains to be seen
whether such concentrations are practical.
HEALTH EFFECTS
In medium to high concentrations (0.5 to >1 ppm) ozone is
known to cause irritation to the eyes and the mucous membranes.
This is probably due to its desiccating effects. In its criteria
document10 for ozone and other photochemical oxidants the
Environmental Criteria and Assesssment Office (ECAO) of the U.S.
Environmental Protection Agency (EPA) summarizes the results of a
large number of studies involving ozone exposures of humans and
animals. These studies paid particular attention to reductions in
lung function. In general, they reported decremental effects in
adults at exposures of 0.37 part per million ozone for 1-3 hours.
A 50% recovery of function took place within a few hours of the
exposures' having ended and a full recovery within 24 hours.
Repeated exposures for long periods of time (6 months to a year)
prolonged full recovery times up to 48 hours. Similar responses
were noted in children and the elderly at concentrations as low as
0.14 part per million. Most of these studies involved some period
of exercise during the exposure cycle, usually 15 minutes of
exercise followed by 15 minutes of rest.
The EPA ambient clean air standard for ozone is 0.12 part per
9
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million for 1 hour. The World Health Organization's air quality
guidelines for Europe set a limit of 0.0 75 to 0.1 part per million
for 1 hour. The Occupational Safety and Health Admins t rat ion sets
the workplace ozone exposure limit at 0.1 part per million for 8
hours.
SUMMARY
Ozone is known to be useful as a biocide for drinking water
and wastewater. However, its use as a biocide in indoor air
settings is limited by the high concentrations that are needed.
Ozone appears to work well against household odors caused by
biocontaminants and ETS; but, because of its byproducts
(formaldehyde, nitrogen oxides etc.), caution needs to be exercised
in its use (at the very least any room so exposed should be aired
afterwards, and such exposures should not take place while the room
is occupied). Ozone has decremental effects on lung function, but
once the exposure is ended there is a full recovery within 24-48
hours. In outside air, ozone promotes many of the reactions that
result in smog. Some of these reactions must also occur in indoor
air, and further studies are needed in this area.
10
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CHAPTER 2
TEST HOUSE STUDIES OF OZONE GENERATORS
The Indoor Air Branch (IAB) of the National Risk Management
Research Laboratory's Air Pollution Prevention and Control Division
maintains a test house where indoor air studies are carried out.
The house is a three-bedroom, single-storey frame dwelling located
in a typical East Coast suburb. It has an attached garage and a
crawl space instead of a basement. Figure 2 shows the floor plan.
This chapter describes a series of experiments carried out in
the test house using commercially available home/office ozone
generators. The purpose of these tests was to document outputs and
transport in a household setting, and no other types of
measurements were taken. IAB did not, for instance, attempt to
ascertain what chemical reactions might be taking place.
OUTPUTS OF THREE OZONE GENERATORS
Three models of home/office ozone generators were tested under
the same general conditions. For the purposes of this report they
will be identified as Unit A, Unit B, and Unit C. Each is equipped
11
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\: Master
..-•' bath
Master
bedroom
Clos I ao$
dos
Bath
Clos
Return
air
Comer
bedroom
aos
Utility
Middle
bedroom
Den
Kitchen
Living
Room
Clos
Instruments
Garage
PI&ORE 2. Test house floor plan
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with controls that allow the user to select fan speeds and ozone
output. In addition, Unit C cones equipped with three insertable
generator plates that allow the user to alter the output range of
the unit. In order to simplify the text, these plates will be
designated Configurations 1, 2, and 3.
Before testing began, a longitudinal and latitudinal traverse
was made of the faces of each of the units at the low, medium, and
high settings. This was done using a TECO Model 565 Ozone
Analyzer. The measurements were averaged and the output calculated
in terms of milligrams per hour. The fan speeds were set at
medium, and the average air speeds were determined with an Alnor
Model 8565 hot wire anemometer. Table 1 presents the results.
TABLE 1. Ozone Generator Outputs at the Face in Milligrams
per Hour.
UNIT CONFIGURATION
A N/A
B N/A
C 1
C 2
C 3
*below limit of detection
LOW
0.00696
0.01992
BLD*
0.00443
0.00554
MEDIUM
0.02690
0.11460
0.00148
0.02772
0.06282
HIGH
0.06720
0.74370
0.03140
0.29298
0.57264
13
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As can be seen, Unit C: Configuration 1: Low Setting had the least
output while Unit B: High Setting had the greatest. It is
interesting to note that for Units B and C the difference in
outputs between the medium and high settings is not double, as one
would expect, but 6 to 10 times greater.
The first set of experiments at the test house were run for
the purpose of determining the maximum sustainable ozone
concentrations that could be achieved in a closed room by each unit
in each of its settings and configurations. The room selected for
the tests was the front corner bedroom (see Figure 2). This room
has a volume of slightly more than 27 cubic meters. All doors and
windows remained shut during the tests, and the heating,
ventilating, and air conditioning (HVAC) system was off. Air
exchange rates were determined using the tracer gas decay method
and averaged 0.3 air exchanges per hour. Each test was run in
duplicate and had a duration of at least 90 minutes. Output
averaging did not begin until concentrations in the room had
reached equilibrium. This normally took 15-20 minutes. The
generator fan speeds were set at medium.
Table 2 shows the results for Unit A. All the data in this
and subsequent tables have, of course, been corrected for the
background.
14
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TABLE 2. Unit A: Maximum Sustainable Ozone Concentrations in
Parts per Billion.
TEST
1
2
3
4
5
6
OUTPUT SETTING
low
low
medium
medium
high
high
AVERAGE OUTPUT
8
14
40
28
200
180
HIGHEST SPIKE
40
60
64
54
320
480
Table 3 shows the same type of data for Unit B.
TABLE
3. Unit B: Maximum
Sustainable Ozone Concentrations in
Parts per Billion.
TEST
7
8
9
10
11
12
OUTPUT SETTING
low
low
medium
medium
high
high
AVERAGE OUTPUT
4.5
6.6
22
15
222
204
HIGHEST SPIKE
22
21
46
36
420
390
15
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Table 4 shows the results for all three of the configurations
of Unit C.
TABLE 4. Unit C: Maximum Sustainable Ozone Concentrations in
Parts per Billion.
TEST
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
*below
BETTING
low
low
medium
medium
high
high
low
low
medium
medium
high
high
low
low
medium
medium
high
high
CONFIGURATION
1
1
1
1
1
1
2
2
2
2
2
2
3
3
3
3
3
3
AVERAGE OUTPUT
BLD*
BLD*
2.2
1.8
19
16
2
2
10
10
140
180
8
8
20
15
140
290
HIGHEST SPIKE
--
—
4.6
5.8
32
24
6
3
15
20
200
240
18
28
35
46
200
460
limit of detection
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Test 29 appears to be an outlier. Configuration 3 requires the
insertion of two plates in the unit, and if one of them were not
making proper contact, the unit would operate as if it was set up
in Configuration 2.
OZONE TRANSPORT
A series of experiments were run to determine how ozone
concentrations in one area of the test house would add to ozone
concentrations in another area. Since ozone decays to O2, this
cannot easily be calculated using interior and exterior air
exchange rates and mass balance equations.
In the first group of experiments, Unit C: Configuration 3 was
set up on a counter in the kitchen of the test house (see Figure
2). An ozone detector was placed in the front corner bedroom.
Tests were then run under four conditions:
Bedroom door open, HVAC off
Bedroom door closed, HVAC off
Bedroom door open, HVAC on
Bedroom door closed, HVAC on
The ozone generator controls were set at maximum ozone output and
maximum fan speed, and all exterior doors and windows were shut.
Table 5 presents the results.
17
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TABLE 5. Transport Tests, Group 1: Ozone Concentrations in
Parts per Billion.
CONDITIONS
bedroom door
bedroom door
bedroom door
bedroom door
AVERAGE
CONCENTRATION
open,
closed
open,
closed
HVAC off
, HVAC off
HVAC on
, HVAC on
50
2
28
38
HIGHEST
READING
72
4
38
54
LOWEST
READING
18
0
14
26
In the tests run with the bedroom door open.and the HVAC off,
there was a constant cycling between the highest and the lowest
readings. All circulating fans have high-low cycles. This is
probably due to the turbulence they create. In this case the
cycling appears to have been accentuated by the distance between
the generator and the detector (approximately 8.5 meters). When
the HVA@ eygtero wag lupned en, hswevif, i goniidipabli erossfehing
took place. This may have been caused by the ductwork acting as a
laminar flow element. It is also possible that the HVAC fan cycle
and the generator fan cycle cancelled each other out.
In another group of transport experiments, Unit B was set up
in the corner front bedroom and allowed to achieve equilibrium
concentrations. Measurements were then taken in the following
locations:
18
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Master Bedroom
Middle Bedroom
Hall
Den
Living Room
Tests averaged 2-3 hours and a minimum of six readings were taken
in each location. These were so consistent that, in the tables
that follow, only one reading for each test will be presented. In
each of these tests all the interior room doors were open and all
the windows and exterior doors were shut. The HVAC system was off
in the first group of tests and on in the second. All tests were
run in duplicate. Tables 6 and 7 present the data.
TABLE 6. Ozone Transport, HVAC Off: Concentration in Parts
per Billion.
LOCATION CONCENTRATION CONCENTRATION
(fan max, gen max) (fan Bed, gen max)
Master Bedroom 120 180
Middle Bedroom 62 70
Hall 120 190
Den 32 16
Living Room 25 ' 26
19
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In Table 6 the smaller concentrations seen with the generator
fan set at maximum are probably due to air dilution. In Table 7
below an even greater dilution is seen with the HVAC fan in
operation. Concentrations, however, are more consistent due to
better distribution throughout the house.
TABLE 7. Ozone Transport, HVAC On: Concentration in Parts
\
per Billion.
LOCATION CONCENTRATION CONCENTRATION
(fan max, gen max) (fan med, gen max)
Master Bedroom 42 no tests run
Middle Bedroom 25 "
Hall 22 "
Den 24 "
Living Room 21 "
OZONE DECAY
The ozone molecule is unstable and has a relatively short half
life. Unless constantly replenished, ozone concentrations will
quickly diminish to background levels. This makes ozone attractive
as an ameliorating agent since, unlike other forms of treatment,
20
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there is no residue of the agent itself (however, as discussed in
Chapter 1, there are reaction products).
This section presents data on ozone decay that were generated
as a byproduct of the previously described tests. The decay rates
presented in the graphs below are a product of both ozone's natural
decay rate and the air exchange rate in the test house during the
test period (0.3 air exchange per hour). In this respect they
present useful data on the decay rates that can be expected in
household settings. All the data were taken with all exterior
doors and windows closed.
Figure 3 shows two representative decay curves from more than
30 generated. These particular curves are for ozone concentrations
in the 160-200 parts per billion range. Notice that the curves are
not asymptotic. This indicates that leakage (air exchange) is not
the dominant process taking place. The variations at the lowest
concentrations may be due to fluctuations in background.
Figure 4 presents the same sort of curves for concentrations
in the 10-30 part§ per billion range, Note that it take§ nearly 2
minutes longer for concentrations to reach zero. This is because,
at the lower measurement range, the instrument detects
concentrations that at the higher ranges would appear to be zero.
As can be seen, the decay of non-replenished, parts per billion
concentrations of ozone in a household setting is rapid and
complete.
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200
Time, Minutes
FIGURE 3.
Ozone decay curves: high range.
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Time, Minutes
FIGURE 4. Ozone decay curves: low range,
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JMMARY
Assuming a continuous 8-hour exposure in a single room
itting, each of the three ozone generators exceeded the OSHA
>rkplace exposure limit of 0.1 part per million (100 parts per
Lllion) by 1.5 to 2 times at their maximum settings. The Food and
rug Administration sets an exposure limit for medical devices,
Deluding air cleaners, of 0.05 part per million (50 parts per
Lllion). At their maximum settings the units exceeded this limit
t nearly 4 times.
In addition, when interior house doors were left open,
I joining bedrooms and the hall were exposed to concentrations that
cceeded one or both of these limits.
For all the concentrations examined, total ozone decay times
Id not exceed 12 minutes.
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References;
1. Weschler, C.'; Hodgson, A.; Wooley, J., "Indoor Chemistry:
Ozone, Volatile Organic Compounds and Carpets,11 Environmental
Science and Technology. 26, 2371-2377 (1992)
2. Atkinson, R.; Carter, W., "Kinetics and Mechanisms of the Gas-
Phase Reactions of Ozone with Organic Compounds under
Atmospheric Conditions." Chemical Reviews. 84-5, 44C-469 (1984)
3. ibid.
4. Hanst, P., "Photolysis Assisted Pollution Analysis,"
privately published by Midac Corporation, Irvine, CA (1994)
5. op. cit.
6. Zhang, J.; Lioy, P., "Ozone in Residential Air: Concentrations,
I/O Ratios, Indoor Chemistry, and Exposures," Indoor Air. 4,
95-105 (1994)
7. Persson, P.; Whitfield, F.; Krasner, S.; Koch, B.; Gramith, J.,
"Control of 2-methyl isoborneol and geosmin by Ozone and
Peroxone," Off-Flavors in Drinking Waters and Aquatic
Organisms. Pergamon Press (U.K.) 291-298 (1992)
8. Indoor Pollutants. National Research Council, National Academy
Press (Washington) 156-165 (1981)
9. Foarde, K.; van Osdell, D.; Steiber, R., "Investigation of Gas-
Phase Ozone as a Potential Biocide," submitted to AFGHE
Journal, not yet published
10. Air Quality Criteria for Ozone and Other Photochemical
Oxidants, Volume 1, Environmental Criteria and Assessment
Office, EPA 600/8-84-020aF (August 1986), NTIS PB87-142956,
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1-156 -1-162
11. ASHRAE, ASHRAE Handbook of Fundamentals. American Society of
Heating, Refrigerating and Air-Conditioning Engineers, Inc.,
Atlanta, GA, 1985, p 22.8.
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APPENDIX
Quality Assurance statement
The work reported in Chapter 2 was covered by the quality
assurance plan for test house gas measurements that was in effect
in the period 1991-1992, and no separate quality assurance plan was
submitted.
The following practises were followed to ensure data quality.
The ozone detector, a TECO Model 560 Ozone Analyzer, was calibrated
against an ozone photometer in accordance with 40 CFR, Part 50,
Appendix D. The photometer that was used is one that is
periodically checked against the National Institute of Standards
and Technology's standard photometer. Variations between the two
instruments did not exceed 0.001 ppm at any concentration. The
ozone analyzer zero was checked at the beginning and end of each
day's sampling and whenever the range was changed. Background
ozone levels were determined at the beginning and end of each test,
averaged, and subtracted from the total measured. Only those data
taken after room ozone concentrations had reached equilibrium (10-
15 minutes) are reported in the chapter. Duplicate, and in some
cases triplicate, tests were run under each set of conditions.
Data from single room tests and some multi-room tests were recorded
on a strip chart recorder and the strip charts preserved. Data
from other multi-room tests were taken manually and recorded in the
sampling log book. Information on times, weather, backgrounds,
sampling conditions, and a number of other factors was recorded in
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the sampling log book and the book preserved. Data on air exchange
rates are a part of the permanent test house data base and are
recorded on disk.
The configuration of the single room tests was as follows.
The ozone detector was placed at the center of the front wall of
the room with the sample intake tube at a height of approximately
3.5 feet. The ozone generator was situated approximately 2 feet
from the center of the back wall on a stand approximately 4.5 feet
high. Previous tests with tracer gases run over several years had
determined that this was a well-mixed room and that, once
equilibrium had been reached, there would be no pockets of higher
or lower concentrations. In the multi-room tests the ozone
generator was placed in the center of the room and faced the door.
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