Environmental Monitoring Series
THE STATUS OF INDOOR AIR
POLLUTION RESEARCH 1976
Final Report
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service, Springfield. Virginia 22161.
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THE STATUS OF
INDOOR AIR POLLUTION RESEARCH
1976
GEOMET, Incorporated
15 Firstfield Road
Ga-it hers burg, Maryland 20760
Contract Number 68-02-2294
Project Officers
S. David Shearer, Jr.
Steven M. Bromberg
Environmental Monitoring and Support Laboratory
Research Triangle Park, N.C. 27711
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, N.C. 27711
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring
and Support Laboratory, U.S. Environmental Protection Agency, and approved
for publication. Approval does not signify that the contents necessarily
reflect the views and policies of the U.S. Environmental Protection Agency,
nor does mention of trade names or commercial products constitute endorse-
ment or recommendation for use.
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CONTENTS
Figures . . vi
Tables . . , ix
Acknowledgement xiii
1.0 Introduction. 1
1.1 Scope 1
1.2 The Survey Process 3
1.3 The Survey Team 4
2.0 An Overview of Indoor Air Pollution Research 5
2.1 Elements of Indoor Air Pollution Research 5
2.2 The Need for Indoor Air Pollution Research 7
2.3 Sources of Indoor Air Pollution 8
2.4 Distribution and Behavior of Indoor Air Pollution. . 11
2.5 Monitoring Technology for the Measurement of
Indoor Air Pollution 13
2.6 Human Occupancy Patterns in Indoor Spaces 15
2.7 Energy Conservation Measures and Their Relation
to Indoor Air Quality 16
2.8 Health Effects of Indoor Air Pollution 19
2,9 Modeling of Indoor Air Pollution 25
2.10 Areas of Further Research Interest 28
3.0 Sources of Indoor Air Pollutants 31
3.1 Outdoor Ambient Air as a Source of Indoor Air
Pollution 31
3.2 Indoor-Generated Pollutants ,60
3.3 An Overview of Research in Indoor Air Pollution
Sources 91
4.0 Distribution and Behavior of Indoor Air Pollutants. ... 93
4.1 S02 and Sulfates 95
4.2 Carbon Monoxide 101
4.3 Carbon Dioxide 118
4.4 Nitrogen Oxides and Nitrates 118
4.5 Photochemical Oxidants 122
4.6 Hydrocarbons (Nonphotochemical Organics) 127
4.7 Particulates 128
4.8 Other Pollutants 134
4.9 Overview of Research in the Distribution and
Behavior of indoor Air Quality 135
(Continued)
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CONTENTS
5.0 Monitoring Technology 137
5.1 Sulfur Dioxide and Sulfates 139
5.2 Carbon Monoxide 142
5.3 Carbon Dioxide 144
5.4 Nitrogen Oxides and Nitrates 145
5.5 Photochemical Oxidants 149
5.6 Hydrocarbons 152
5.7 Particulates 156
5.8 Conclusions 163
6.0 Building Occupancy 166
6.1 Occupancy Profiles 166
6.2 Human Activities 173
6.3 Overview 179
7.0 Energy Conservation Measures in Buildings 180
7.1 Introduction 180
7.2 Energy Conservation Modifications 181
7.3 Building Climatology and Relationships Between
Indoor Air Quality and HVAC Systems 245
8.0 Health Effects 256
8.1 Sulfur Oxides 259
8.2 Carbon Monoxide 268
8.3 Carbon Dioxide 273
8.4 Nitrogen Oxides 275
8.5 Photochemical Oxidants 282
8.6 Organic Pollutants 289
8.7 Particulates 304
8.8 Air Pollution and Lung Cancer 319
8.9 Susceptibility of Population Subgroups to Indoor
Air Pollution 322
8.10 Interactive Pollutant Effects 325
8.11 Evaluation of Indoor Air Pollutant Health Hazards
and Research Priorities 327
9.0 Modeling of Indoor Air Pollution 336
9.1 Objectives 336
9.2 Limits of Current Research 337
9.3 Elements of Indoor Air Pollution Modeling 340
9.4 The Modeling Process 342
9.5 Model Parameters 347
9.6 Conclusions 349
(Continued)
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Contents
Appendices
A. Modeling of Indoor Air Pollution 352
A.I Background for Indoor Air Pollution Modeling
Effects 352
A.2 Simulation Models 356
A.3 The State-of-the-Art of Definition of Model Input
Parameters. . - 412
A.4 A Provisional GEOMET Design for an Indoor Air
Pollution Model 422
A.5 Use of Tracer Gases in Measurement of Ventilation
Rates and Other Aspects of Indoor Air Pollution
Models 423
A.6 Conclusions 429
B. General Bibliography 432
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FIGURES
Number Page
1 Scatter diagram of relationship between simultaneous
24-hour averages of indoor and outdoor sulfur
dioxide on one locality 38
2 Indoor/Outdoor profile for winter CO data in
Hartford, Connecticut 42
3 Scatter diagram of relationship between simultaneous
24-hour averages of indoor and outdoor suspended
particulate matter in one locality 57
4 Relative NO levels as recorded outdoors (1), indoors
(2), and as reported by the Pasadena APCD station
(3) on a typical day 121
5 Ozone concentration vs. time of day for Thomas
Building, August 8, 1971 124
6 Ozone concentration vs. time of day for Spa!ding
Laboratory, June 27, 1971 124
7 Ozone concentration vs. time of day in private home
in Altadena, July 25, 1971 124
8 Apartment house 167
9 Elementary and high schools 168
10 Shopping center 169
11 Computer model occupancy profiles - residence 172
12 Profile of persons sleeping 174
13 Profile of persons engaged in watching TV, rest, and
relaxation 174
14 Appliance load profile 175
(Continued)
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FIGURES
Number Page
15 Floor plan of characteristic house 182
16 Window perimeter crack length as a function of area. . . 189
17 Air flow around single-family dwelling as a function
of orientation with respect to wind direction 192
18 Air flow around townhouse or low-rise apartment
building as a function of orientation with respect
to wind direction 193
19 Window components which contribute to the residence
to heat flow 202
20 Infiltration rates as a function of wind speed and
ventilation rate 216
21 Infiltration rate for a 15 mph wind as a function of
ventilation rate 217
22 Typical performance data for electronic air cleaners
reproduced from technical options for effective
residential energy conservation measures 220
23 Experimental data illustrating the influence of the
building climatology on the air infiltration 248
24 Typical decay curves for sulfur dioxide and ozone. ... 251
25 Reference data for sulfur oxides air quality
criteria 260
26 Reference data for carbon monoxide effects 272
27 Reference data for nitrogen dioxide air quality
criteria 276
28 Air quality criteria for photochemical oxidants. .... 285
(Continued)
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FIGURES
Number Page
29 Reference data for particulate air quality criteria. . . 308
30 Elements of a pollutant hazard rating model 329
31 Major functional relations in indoor air pollution
modeling 341
32 Schematic representation of indoor pollution model
equation 346
A-l Linear approximation of flow equation 372
A-2 Schematic representation of a ventilated enclosed
space 404
A-3 Schematic diagram of ventilation model 408
A-4 Infiltration rate as a function of temperature
difference between inside and outside 428
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TABLES
Number Page
1 Average Indoor/Outdoor Ratios of Sulfur Dioxide (S02)
As Measured in Buildings by Various Investigators ... 37
2 Sulfur Dioxide Seasonal Averages (PPHM) and Day-Night
Ratios at Four Public Office Buildings in Hartford,
Connecticut 39
3 Sulfur Dioxide Seasonal Averages (PPHM) and Day-Night
Ratios at Two Houses in Hartford, Connecticut 40
4 Summary of Carbon Monoxide Results, PPM (Indoor/Outdoor
Ratio, Dimension!ess) 42
5 Average Indoor/Outdoor Ratios of Suspended Particulate
Matter (SPM) 56
/
6 Summary of Pollutant Emissions of Gas Appliances for
Several Typical Operating Conditions in Hartford
Dwellings 63
7 Pollutant Concentrations* Related to Various Utensils . . 65
8 Gaseous Air Pollutants Observed in Homes with Gas Ovens . 67
9 Effect of Gas Burner Conditions on Gaseous Emissions. . . 68
10 Gas Kitchen and Outdoor Concentrations of W>2 and CO. . . 69
11 Active Ingredients in Common Aerosol Spray Product
Classes 84
12 Aerosol Usage Patterns by Aerosol Product Category in
TRC Households 85
13 Concentrations of S02 Absorbed by Various Materials ... 98
14 Mechanisms by Which Sulfur Dioxide is Converted to
Sulfates 102
(Continued)
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TABLES
Number Page
15 Known Atmospheric Sulfates 103
16 Summary of Indoor/Outdoor CO Data in Each Home for
Both Seasons. . 108
17 Measured Concentrations of Carbon Monoxide in the
Exposure Chamber from Total Cigar Smoke for One
Cigar Smoked at Each of 1, 3, 6, and 8 Volumetric
Air Changes/Hour Ill
18 Measures of CO and SPM in an Exposure Chamber 113
19 Estimate of CO Concentrations in a 9.2 m3 Room
Occupied by a Smoker and a Non-Smoker . . . 113
20 Concentrations of CO Recorded in Ice-Skating Arena
During Operation of Propane-Powered Ice-Resurfacing
Machine Generated for 10 Minutes Every 1 or 2 Hours . . 115
21 Results of Initial Survey of Carbon Monoxide Levels
in Ice Skating Arena in King County, Washington .... 115
22 Concentrations of NO and NOe (ug/m3) Observed in Homes
with Gas Ovens 119
23 .Measured Values of Ozone Decomposition Rates for
Several Common Surfaces .... 126
24 Results of Tests of Ozone-Decomposition Catalytic
Efficiency of Various Materials 126
25 Concentration and Size of Trace Metal Particles in
Urban Air 131
26 Trace Metals in Fly Ash as a Function of Particle
Size 131
27 Continuous Monitoring Equipment Specifications Employed
for Monitoring Indoor-Outdoor Pollutants 164
(Continued)
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TABLES
Number Page
28 Intermittent Sampling and Analytical Methodology
for Indoor-Outdoor Pollutant Monitoring 165
29 Percentages of Individuals Performing an Activity
One Time or More During a Weekday and the Mean
Durations of the Activity, for Metropolitan United
States 178
30 Design Parameters for Characteristic House 183
31 Insulating Effects Due to the Addition of Storm Doors
and Storm Windows 186
32 Comparison of Values With and Without Insulation 200
33 Benefits of Insulating Shutter 203
34 Heat Pump Improvements 231
35 Gas-Fired Furnace Improvements 235
36 Oil-Fired Furnace Improvements . 236
37 Effect of Relative Humidity on Ozone Decomposition in
Aluminum Chamber 249
38 Summary of Rate Constants Obtained in Various Enclosed
Areas 249
39 Values for k, ti/2, and Vq at Various Relative
Humidities. 252
40 Reactivity Levels from Irradiation of 1.63 ppm C
Ethylene * 0.50 ppm NO in the Presence of Various
Water-Vapor Levels 252
41 Best Judgment Estimates of Pollutant Thresholds for
Sulfur Oxides and Suspended Particulates 265
(Continued)
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TABLES
Number
42 Effects of Controlled Ozone Exposure on Adult
Males 287
43 Illustrative Health Information on Some Household
Solvents and Cleaners 292
44 Illustrative Summary Information on Selected
Pesticides 303
45 Elements of a Pollutant Hazard Ranking Methodology. . . . 328
46 Indoor Air Pollution Models - Inputs - Outputs -
Assumptions 339
A-l Energy Models - Methodology - Inputs - Outputs 357
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ACKNOWLEDGEMENTS
This report, prepared for the Environmental Protection Agency
by GEOMET, Incorporated, is the work of many people.
Researchers and writers included J. Howard Beard, III, James E.
McFadden, Dr. Demetrios J. Moschandreas, John S. Norton, Scott D. Thayer,
and John R. Ward of GEOMET; Craig H. Caldwell, Lawrence A. Elfers, George
A. Jutze, and Anthony S. Wisbith of PEDCo Environmental Specialists,
Incorporated; and Taghi Alereza, Harvey M. Bernstein, Burton Karpay and
Daniel W. Talbott of Hittman Associates Incorporated. John L. Swift of
GEOMET was editor of the report.
GEOMET consultants who reviewed the report in draft form and
provided advice were Drs. John E. Davies, Robert R. Henderson, Ian T.T.
Higgins, Abraham M. Lilienfeld, Fredrick H. Shair and .Ralph G. Smith.
Among EPA scientists at Research Triangle Park who reviewed drafts and
helped to shape the report were Robert M. Burton, Dr. Diane G. Fogleman,
Walter B. Steen and the EPA Project Officer for the GEOMET contract, Dr.
S. David Shearer. The help provided to GEOMET by the consultants and by
EPA reviewers was of great value, but they are in no way responsible for
our views or for our errors of commission or omission.
J.L.S.
Gaithersburg, Maryland
October 8, 1976
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Section 1.0
INTRODUCTION
Much research has examined the occurrences of air pollution in
outdoor and workplace environments. A smaller, newer body of research has
examined air pollution in nonworkplace, indoor environments. A new
emphasis on measures to conserve energy in buildings, curbing heat loss
through reduced indoor-outdoor air exchange, has encouraged interest in
the relation between indoor and outdoor air quality, building energy con-
servation, and the potentials for adverse health effects from indoor air
pollution in nonworkplace environments. A review of this body of research
is the subject of this report. The review was performed for the Environ-
mental Monitoring and Support Laboratory of the U.S. Environmental Protection
Agency, at Research Triangle Park, North Carolina, by GEOMET, Incorporated
under Contract No. 68-02-2294, dated March 8, 1976.
1.1 SCOPE
The contract assignment which resulted in the preparation of
the present report required a comprehensive survey and assessment of the
state-of-the-art of indoor air pollution research described in published
literature and unpublished ongoing research. GEOMET was requested to
consider:
Sources of air pollution in dwellings, schools,
public buildings and vehicles
Influences of outdoor air quality and meteorological
conditions on indoor air quality
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Usage of products which serve as sources
of indoor air pollutants
a Technology for monitoring indoor air pollution
Mobility, dispersion characteristics, decay, and
reactivity of indoor air pollutants
Occupancy by humans of indoor air spaces
a Energy conservation measures presently being
utilized in nonworkplace buildings
Changes in indoor air quality as a function of
energy conservation
Health effects associated with characteristics
of indoor air pollutants, including a rank order-
ing of air pollutants in terms of the hazard to
human health resulting from their occurrence in
nonworkplace indoor environments.
The basic survey and the preparation of its draft report were
performed, as provided in the contract assignment, in the four-month
period from March to July, 1976. Reviews of the draft by concerned EPA
scientists and consultants were made between July and September, resulting
in the completion of the report in October 1976.
This report is the culmination of the first phase of GEOMET's
work under its EPA contract. A parallel continuing effort is the conduct
of a program of field monitoring of indoor air pollution and energy use
parameters in residences and schools which began at the end of June 1976
and is to be completed in the first half of 1977. The data from this
program, with analyses and steps toward an improved indoor pollution model,
will be available in a report to be issued in late 1977.
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1.2 THE SURVEY PROCESS
The survey was performed through an examination of relevant
published literature (reviewed journal articles, technical reports, and
other publications) supplemented by personal communications with some
researchers in the field. The literature examined was selected through
the preliminary assembly and review of bibliographies of literature of
likely relevance to indoor air pollution research. Research and docu-
mentation were considered relevant if they dealt with indoor air pollution
in any of its aspects, with energy conservation measures which could affect
indoor air quality, or with the health effects of pollutants in an indoor
environment. Several approaches were taken to obtain bibliographies. These
included:
1. Use of bibliographies previously prepared specifically
for indoor air pollution research.x Among these were
Indoor/Outdoor Air Pollution Relationships: Vol. II,
An Annotated Bibliography, EPA Publication No. AP-111
2b by J.J. Henderson, F.B. Benson and D.E. Caldwell,
published in 1973; and a 190-entry bibliography of
indoor air pollution research prepared by GEOMET from
various sources in October 1975.
2. Discussion with EPA professional staff and with GEOMET
consultants, for identification of relevant recent
research papers.
3. Examination of recent volumes of NTIS Air Pollution
Abstracts and Environment Abstracts and of such
periodicals as Journal of the Air Pollution Control
Association, Environmental Science and Technology
and Archives of Environmental Health.References
cited in relevant periodical articles were a further
source of bibliographic information.
4. Visits to major libraries such as National Library of
Medicine, the EPA Library at Waterside Mall, Washington,
D.C., The EPA Library at West St. Clair, Cincinnati, the
PHEW Library at the Park!awn Building, Rockville,
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Maryland, the Library of Congress, the National Associ-
ation of Home Builders Library, Washington, D.C., the
libraries of the University of Cincinnati and Mi ami
University (Oxford, Ohio) and others.Computerized
bibliographic searches were made through the Smithsonian
Science Information Exchange, through Medlars at the
National Library of Medicine and through the National
Agricultural Library at Beltsville, Maryland.
Where available, abstracts or summaries of articles identified
in the bibliographic search were scanned. Articles which appeared to be
relevant on the basis of abstract, summary, or title (if only the latter
were available) were obtained and examined. If relevance was confirmed
the document was listed for inclusion in the Bibliography (Appendix B)
of the present report. In general, documents listed in Appendix B have
been examined by authors of this report. This is not always the case.
Some documents not examined are listed only because their relevancy was
cited by researchers whose studies are referred to in this present report.
1.3 THE SURVEY TEAM
This report has been prepared by a multidisciplinary project
team directed by GEOMET, Incorporated. GEOMET provided overall management
for the literature review and report production, and members of the GEOMET
staff undertook the health effects, air quality analysis, and modeling
aspects of the study. GEOMET was supported by the efforts of two sub-
contractors: Hittman Associates, Inc., for energy conservation and
PEDCo Environmental Specialists, Inc. for air pollution monitoring technology.
GEOMET consultants from several universities, in the fields of epidemiology,
monitoring, and modeling of indoor air pollution, have provided advice
to the project.
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Section 2.0
AN OVERVIEW OF INDOOR AIR POLLUTION RESEARCH
Air pollution and its effects on human health have been studied
in outdoor, industrial and indoor environments. This report is concerned
with indoor air pollution research, and particularly with residential and
other nonworkplace indoor environments.
2.1 ELEMENTS OF INDOOR AIR POLLUTION RESEARCH
Indoor air pollution research is potentially a large field. It
is defined, for the purposes of this report, to include the following areas
of study:
Sources of Indoor air pollution
Distribution and behavior of indoor air pollution
Monitoring (measurement) technology for indoor air
pollution
t Building occupancy and human exposure to air pollution
Energy conservation measures in buildings which may
affect indoor air quality
Health effects of indoor air pollution
Modeling (estimation and prediction) of indoor air
pollution behavior.
Published literature and other available information in these
fields are described in this report. Emphasis has been placed upon research
in the nonworkplace, indoor environment, but the study cannot easily b. so
constrained.
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Much relevant research has been performed 1n environments which
do not meet the basic criterion of being "nonworkplace." University and
private laboratory buildings have been sites of important research in
emissions of indoor-generated pollutants and of research into Indoor-outdoor
air pollution concentration ratios. Hospital environments have been
monitored for allergen and other biological aerosol concentrations. Work
performed in such areas has been referred to in this report when its
results appear to be also applicable to nonworkplace environments.
In the field of health effects of indoor air pollution it is
especially necessary to examine studies which are not limited to residential
and other nonworkplace environments. With the exception of the considera-
tion of clinical effects of carbon monoxide exposure there have been few
clinical or epidemiological studies of the impact of indoor air pollution
upon human health in which any effort was made to identify the human
exposure indoors, within residences, public buildings, schools or vehicles,
as being a separate category of air pollution exposure. More typically,
health effects studies have correlated health status changes with ambient
(i.e., outdoor) air pollution levels, or with specific and (from the point
of view of the nonworkplace environment) unusual exposures of individuals
to air pollution 1n industrial workplaces. The effort made in the present
report, to appraise the status of research in and knowledge about indoor
air pollution health effects, therefore draws upon the broad base of
research performed in industrial environments and in the general field of
ambient air pollution epidemiology as well as upon research in nonworkplace
indoor environments.
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In the discussions which follow immediately, Sections 2.3
through 2.9, the state of research in the seven areas of interest 1s
summarized briefly. No literature citations appear here, but the text
is based in each case upon a more detailed exposition given later in
Sections 3 through 9, where specific literature citations will be found
for all statements and conclusions drawn from the work of researchers
in the Indoor air pollution field.
2.2 THE NEED FOR INDOOR AIR POLLUTION RESEARCH
Why make a special study of indoor air pollution? Are its
characteristics and consequences sufficiently different from air pollution
in the already active fields of ambient and occupational air pollution
research to justify the definition of a new field of study? The answer
appears to be yes.
The major thrust of air pollution research, and of air pollution
control and regulation, has historically been toward protecting human
health and welfare from air pollution damage in outdoor and occupational
situations. These two contexts each have characteristic and quite different
air pollutant species, concentrations and human exposures. There is a
reasonable presumption, borne out by the research reviewed in this report,
that the indoor nonworkplace environment represents a third major context -
one in which the pollutant species present, their concentrations, and the
nature of human exposure are significantly different from the situations
which prevail outdoors and in workplaces. Further, the nonworkplace, indoor
environment 1s one in which many people - particularly homemakers, children
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and the elderly - spend the major part of the time. The air pollutants
to which they are exposed are not necessarily those of ambient air. As
the details of this report will show, pollutants occurring within buildings
may reach levels at which exposures of significant importance to health
occur. The character, intensity and duration of these indoor air pollution
exposures are unlike those occurring in the better studied ambient and
occupational contexts, sufficiently so to require new research into their
origin, behavior and consequences.
The differences between indoor and outdoor pollution exposures,
and the potential consequences of indoor pollution exposures, may in the future
justify the setting of national standards directed toward the control of
nonworkplace indoor air pollution levels in the protection of human health
and welfare. There are as yet no such standards. Research into the occur-
rence and consequences of indoor air pollution is an essential prerequisite
for defining the hazard and designing means for its control.
There is enough evidence now to make it clear that a potential
indoor air pollution health problem exists. More research is needed to
determine its extent and amenability to management. The status of current
research is described in some detail in the main text of this report,
Sections 3 through 9. An overview of this research appears below.
2.3 SOURCES OF INDOOR AIR POLLUTION
There are two major source categories of indoor air pollution:
(1) infiltration from outdoor ambient air and (2) generation of pollutants
1n the indoor environment.
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Pollutants entering buildings from outdoor ambient air include
sulfur dioxide, nitrogen oxides, carbon monoxide, hydrocarbons, oxidants,
and suspended participates (i.e., the so-called "criteria" pollutants
for which National Ambient Air Quality Standards exist). Other pollutants
of outdoor origin for which researchers have considered indoor/outdoor
concentrations have included the respirable fraction of particulates,
trace metals, biological aerosols, carbon dioxide, carbon disulfide,
hydrogen sulfide and peroxyacetyl nitrate (PAN). For almost all
outdoor-generated pollutants, researchers have found that concentrations
Indoors are lower than outdoors (unless there is a separate source for
generation of the pollutant within the building). Indoor-outdoor ratios
are high, approaching and sometimes exceeding unity, for carbon monoxide
(an unreactive gas). Sulfur dioxide and ozone react chemically with
substances in the indoor environment and hence show typically lower
indoor-outdoor pollutant concentration ratios (varying from 0.20 to 1.0
for sulfur dioxide, 0.65 to 1.0 for ozone). Suspended particulates show
concentration reductions below outdoor levels, although indoor sources
of particulates and lack of particulate size distribution studies make
the significance of indoor-outdoor ratios for particulates unclear.
There is little information on indoor-outdoor ratios for nitrogen oxides
and hydrocarbons; the few studies noted suggest that indoor-outdoor con-
centration ratios are high.
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Actual measurements of the effective source strengths (i.e.,
of the sum of planned and unplanned infiltration into the building) have
not often been made for outdoor-generated pollutants. Ozone infiltration
rates have been calculated with the aid of tracer studies and a theoret-
ical model, but the more typical research procedure has been to simply
measure pollutant concentrations (parts per million by volume, or weight
of pollutant per unit volume) inside the building and outside it. The
resulting indoor-outdoor concentration ratio, generally reported in the
literature, is related to the rate at which the pollutant enters the
building but it cannot be used alone to calculate source strengths. The
indoor-outdoor concentration is dependent not only upon the entry rate
of the pollutant but also upon the relative locations of indoor and
outdoor sampling points upon the internal ventilation system of the
building, the time periods involved in monitoring, and upon the reactiv-
ity of the pollutant with substances within the building. With the
exception of some measurements for ozone, there are no indications in
the literature of the quantities and rates in which outdoor-generated.
pollutants enter buildings.
Indoor-generated pollutants include carbon monoxide; carbon
dioxide, nitrogen oxides and sulfur dioxide from indoor combustion;
particulate matter and chemical vapors from household cleaning; halo-
genated hydrocarbons from solvents; mercury from paints; propel1 ants and
active ingredients of aerosol spray products; carbon monoxide, particu-
lates, nicotine and other chemicals from smoking; aldehydes from cooking
and many others. There has been considerable research into combustion
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product pollutants in the indoor environment, including measurements and
calculations of source strengths. Estimates of pollutant emissions have
been made for aerosol spray product propellents, and to some extent for
the airborne pollutant products of smoking. Emission rates for the active
s,
ingredients of aerosol spray products have been difficult to estimate in
the absence of sophisticated monitoring and laboratory technology -
because the exact nature and proportions of such ingredients are pro-
prietary information not usually disclosed by manufacturers. Source
strengths have typically not been reported in the literature for the
"fugitive" type of indoor pollutant emissions, such as those arising
from diffuse sources in cleaning, food preparation, pesticide application,
painting and hobby activities.
2.4 DISTRIBUTION AND BEHAVIOR OF INDOOR AIR POLLUTION
The concentration, residence times and decay rates of the
standard major ambient air pollutants, S02, NO, N02, CO, 03 and sus-
pended particulates (also called the National Ambient Air Quality
Standard criteria pollutants) have been extensively studied in indoor
environments. Much of this research has been concerned with indoor-
outdoor concentration ratios, evidence of a tacit assumption by many
researchers that outdoor sources of air pollution are the important
ones for indoor air pollution.
Building ventilation and indoor climatology have a major
influence on the transport, diffusion and removal of indoor pollutants.
These influences have been studied for the standard pollutants in the
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Indoor-outdoor context. Data collected 1n these studies typically pro-
vide gross or partial measures of pollutant behavior, without the fine
structure needed to permit the making of conclusions about dimensional
pollutant gradients and behavior within a building. The building (Indoor
space) 1s generally treated as a plenum (or whole) Interacting with the
outdoor space. Differing air pollution characteristics 1n different
parts of a building - necessary to determine human pollutant exposure
and dosage -'have not often been considered 1n research performed in the
past. Research data on the Indoor decay of introduced ambient reactive
pollutants show definite relationships between pollutant decay and indoor
climatology. There appears to have been no important research dealing
with indoor chemical formation of secondary pollutants, e.g., sulfates
and nitrates. In general, the area of chemical transformation and fate
of indoor pollutants has not been addressed in depth.
Data on Indoor emissions (source strengths) of the standard
pollutants are uncommon in the literature, except for measurements on
the production of carbon monoxide and nitrogen oxide in gas stoves.
This scarcity is probably a function of the considerable technological
difficulty in making emission measurements of the uncontrolled gener-
ation of air pollutants when these appear indoors from stoves, leaky
furnaces, smoking and other diffused sources. Measurements of quanti-
ties of propel1 ants in aerosol sprays, and of some combustion products
of tobacco smoking, have been made; these are essentially calculations
of source strength from known ingredients rather than actual measurements.
Aerosol and smoking pollutant source strengths have been correlated with
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pollutant concentration measurements to produce Information about decay
^s
rates; but such source strength-indoor concentration comparisons are
rare in the literature of research into indoor-generated pollutants.
The data tend to be partial, providing pollutant concentrations but not
pollutant behavior histories.
2.5 MONITORING TECHNOLOGY FOR THE MEASUREMENT OF INDOOR AIR POLLUTION
Indoor air quality monitoring technology relies heavily upon
the technique and instrumentation earlier developed for ambient air
monitoring and for Industrial hygiene monitoring. Adaptations in tech-
nology must be made for the special circumstances of the indoor environ-
ment.
In outdoor (ambient) air pollution monitoring the instruments
used for making measurements do not significantly alter the environment
in which they operate. They are infinitesimally small in physical size
and in air intake requirements compared to their environment. This is
not the case for indoor air monitoring. A high volume air pump of the
type conventionally used to monitor ambient particulate through trapping
particles on a filter for weighing could sensibly alter the concentration
of partlculates in the air inside a house because its flow rate is high
enough to exchange all the air in a large room in an hour. Further, the
size and noise of its operation would impede normal use of any indoor
space in which it is placed. Instruments for indoor use must be physically
smaller than outdoor instruments. The analyzers, filters and pumps may
need to be located remotely from the sampling points. Flow rates of intake
air must be small and this often requires higher threshold detection levels
and instrument sensitivities than are customary 1n ambient air monitoring.
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The range of pollutants to be monitored 1s wide; wider than the
usual outdoor ambient concern which is largely limited to the National
Ambient Air Quality Standards criteria pollutants, their transformation
products and trace metals. Many of the pollutants of concern in indoor
residential spaces have been routinely monitored in the past only under
laboratory conditions or in industrial situations where the pollutant
concentrations are high.
Many indoor-generated pollutants are emitted in a "fugitive"
manner, I.e., they enter the atmosphere through uncontrolled emanation
from surfaces, leaks from faulty combustion systems, or from other
sources 111-defined in place and form. It 1s difficult to measure source
strengths for such pollutants; conventional emissions monitoring tech-
niques are not applicable. Innovative measurement techniques, involving
combinations of pollutant concentrationsmonitoring, controlled tracer
gas measurements and simulation modeling may be required.
One approach to the problem of avoidance of altering the Indoor
environment through monitoring has been to place the analyzers, filters
and pumps in a mobile monitoring van located outside the building in
which pollutant behavior is to be measured. The sampling inlets,
located In the building, are connected to the analyzers by long, small-
diameter, flexible tubing passing through closed windows or other openings
In the building's outside wall. Special problems of air flow and possible
pollutant loss in the tubing are involved; but these are solvable.
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The Instruments used 1n indoor air monitoring operate upon
physical and chemical principles already demonstrated, for the most part,
1n ambient and Industrial air pollution monitoring. The differences are
1n the details required for the special indoor conditions suggested above,
not in principles.
2.6 HUMAN OCCUPANCY PATTERNS IN INDOOR SPACES
Levels of indoor air pollution are in part a function of the
activities of occupants of indoor spaces. People affect the indoor-outdoor
pollutant concentration relationships by opening and closing doors and
windows and by controlling operations of heating, ventilating and air con-
ditioning systems. People also create indoor air pollution inside buildings
through such actions as sweeping, using aerosol sprays, cooking, smoking
and breathing.
The hazard of air pollution to human health is a function of
pollutant toxicities and human dosages. Dosages are functions of exposures,
which In turn are functions of the strengths, durations and locations of
pollutant concentrations and of the locations and types of activity of
people who occupy the spaces contaminated by air pollution. For these
reasons studies of human movement and activity in buildings are needed to
0) provide additional information about indoor pollutant generation and
distribution and (2) make it possible to estimate human exposure to indoor
air pollution; but few studies directed towards those objectives have been
undertaken.
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Occupancy profiles have been developed by investigators, display-
ing the levels of occupancy in buildings as a function of time. These are
typically gross patterns, showing occupancy of an entire building averaged
over periods of an hour or more. They are of more value to the design of
heating, ventilation and air conditioning systems than they are for indoor
air pollution generation and exposure studies. A finer detail of the time
and place of indoor human movement is required than appears to be now avail-
able in the scientific literature.
Activity patterns add some of the desired detail, by classifying
human activities into various categories which can be at least indirectly
related to pollutant-creating or pollutant exposure situations. But studies
of activity, as performed in the past, do not yet adequately relate activ-
ity events inside buildings to the times and places at which pollutant con-
centrations may be measured or predicted.
2.7 ENERGY CONSERVATION MEASURES AND THEIR RELATION TO INDOOR AIR QUALITY
Energy is supplied to buildings to maintain indoor conditions of
temperature, humidity and air flow which meet human requirements for health
and comfort. These conditions are maintained by the static considerations
of building design (orientation, layout, volume, shape, materials, planned
openings - windows and doors - and unplanned openings - cracks - in the
exterior wall) and the dynamic operation of the building heating, ventila-
tion and air conditioning (HVAC) system including mechanical equipment and
window opening and closing. Energy is required to operate the HVAC system.
The HVAC system moves energy in the building, as heated or cooled air, and
transfers energy from the building to the outdoors by venting air. Energy
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also enters the butiding from the outdoors whenever exterior temperatures
are htgher than Interior If building design and operation does not prevent
the heat transfer.
Energy can be conserved 1n buildings by minimizing heat flow from
the building to the outside. This can be done by methods which affect build-
ing air change rates, reducing the flow of air between indoors and outdoors,
and by methods which do not directly affect air change rates.
Among the possible structural modifications which save energy by
reducing air change rates are installation of storm doors and windows to
reduce infiltration (air leakage), caulking and weatherstripping, painting,
use of smaller windows, improved orientation of the building with respect
i
to wind and sun exposure, elimination of fireplaces, use of recirculating
kitchen hoods, vestibule doors, door closers, and windbreak landscaping.
Structural building modifications which save energy but do not
directly affect air change rates include: insulation of walls, roofs and
floors, double-glazing of windows, improved thermal capacities of building
materials, shading for windows, fluorescent lighting instead of incandescent,
elimination of gas-burning pilot lights, reduction of the ratio of building
envelope to floor area, ventilation of attic spaces, using appropriate
external building colors, and lower ceiling heights.
Modifications to the HVAC system and its operation which save
energy by reducing the indoor-outdoor air change rates include installation
of flue dampers, use of outdoor air for combustion, installation of an
economizer air conditioning cycle, internal pressurization, filtration and
re-use of ventilation air, reduction in percentage of outdoor air intake,
reduction in ventilation rate, and improved ventilation control.
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Modifications of the HVAC system to save energy which do not
affect air change rates include: recovery of flue gas heat through heat
exchange devices, zone control of the HVAC system inside the building,
separate make-up air for high exhaust rate areas, humidity control,
proper sizing of equipment, improved furnace design, nighttime tempera-
ture setback, and regular maintenance.
Human life-style habits also impact on energy use and loss in
buildings. Energy savings can be achieved by keeping windows closed,
minimizing use of exhaust vents, minimizing exit and entry to buildings -
all these reduce air change rates. Life-style habits which save energy
without directly affecting air change rates include use of lower thermo-
stat settings in winter and higher settings in summer, reduced use of
large appliances and lower lighting levels.
All the energy conservation actions which reduce indoor-outdoor
air change rates also impact directly on indoor air pollution levels,
essentially by tending to reduce the indoor levels of outdoor-generated
pollutants, while increasing residence times of indoor-generated pollutants.
The operation of the HVAC system, if it is equipped with filters, precipi-
tators or washers, may remove some portion of the particulate matter in
the air and some portion of the reactive pollutant indoor air concentra-
tions of species such as SCL and oxidants. A reduction in air change rates
may reduce this removal rate, resulting in somewhat higher levels of pol-
lutants than might otherwise be expected; this effect is small and may be
masked by the reduction of infiltration of outdoor pollutants. Changes
in building temperature and humidity impact upon decay rates of reactive
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pollutants; typically decay rates increase with rising temperature and
humidity, meaning that the pollutant concentrations reduce more rapidly.
This may or may not be desirable from the health point of view, since
the pollutant transformation products in conditions of heightened tem-
perature and humidity may adversely impact on health.
There have not been quantitative studies linking measured param-
eters of energy conservation, and of HVAC operation for energy conservation,
with changes in indoor air pollution levels. Such studies are a desirable
objective for future research.
2.8 HEALTH EFFECTS OF INDOOR AIR POLLUTION
Many people spend a major part of their lives 1n nonworkplace
indoor air environments, exposed to air pollution which differs significantly,
1n type and level, from the better-studied ambient and occupational air
environments. What are the health hazards of these exposures?
The question has been little studied in the specific context
of the nonworkplace indoor environment. Population studies correlating
general ambient air pollution levels and health status are reported 1n the
literature for the more common, widespread ambient pollutants; a number of
these studies have considered synergistic effects of pollutant combinations.
Such studies in years prior to 1971 were the basis for the establishment
of National Ambient A1r Quality Standards for the six "criteria" pollutants -
sulfur dioxide, carbon monoxide, nitrogen oxides, photochemical oxidants,
total nonmethane hydrocarbons and total suspended particulates - to protect
public health and welfare. Many other studies of health effects of specific
pollutants have been made in the context of occupational exposures, often
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dealing with pollutant concentrations higher than would usually occur in
other environments. The scientific literature relevant to indoor air pollu-
tion is largely to be found 1n these related fields of ambient and occupational
air pollution health effects.
The review upon which this report is based has examined the litera-
ture for the purposes of (1) identifying the health effects of those pollutants
most likely to occur in nonworkplace indoor environments, (2) considering
the interactive effects of pollutants, (3) considering the susceptibility of
population subgroups to indoor air pollution hazards, and (4) attempting to
develop a rationale for appraising the relative health hazard of various
indoor pollutants.
Indoor, outdoor and occupational air pollution health effects
cannot readily be separated. The effort here 1s not to consider the health
effects of Indoor air pollution 1n isolation, an Impossible task, but to
examine the existence and role of indoor air pollution as a significant
factor 1n the overall problem of air pollution impact upon human health.
From the literature of general and occupational air pollution
health effects studies, there 1s adequate evidence to substantiate the
health hazards, Indoors and outdoors, of the so-called "criteria" air
pollutants. The level of knowledge about the health effects of these
major air pollutants is uneven. The synergistlc effects of S02 and partlcu-
lates and of S02 and sulfates in producing both acute and long-term respira-
tory system problems are well documented, but the adverse impacts of SOp
alone at common ambient levels are less well understood. Sulfur dioxide
exposure is probably typically lower indoors than outdoors. The dose-effect
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relationship of carbon monoxide is well-established and a substantial
amount of research into its cardiovascular impact continues. The subject
is an important one because carbon monoxide may occur at high indoor levels
from several sources, including gas stoves and smoking. Carbon dioxide, a
noncriteria pollutant but one which may occur in high levels indoors,
can produce adverse health effects through oxygen deprivation, but the
evidence suggests that pollutant levels high enough to cause this will be
rare in nonworkplace indoor environments. Nitrogen dioxide has been less
studied than sulfur dioxide and carbon monoxide; its correlation with acute
respiratory disease has been demonstrated and studies of this aspect con-
tinue. Nitrogen dioxide has also been implicated in long-term respiratory
problems and with increased mortality from cardiovascular disease and
cancer, although the evidence is less clear than for acute respiratory
disease. Like carbon monoxide, nitrogen oxides are a potentially common
Indoor pollutant associated with gas stoves. Photochemical oxidants have
well-documented, short-term irritative effects but long-term effects are
not well understood; however, they may not be a significant indoor problem
because of the rapid decay of reactive oxidants in indoor environments.
Total suspended particulates, a "criteria" pollutant, are impli-
cated as a group in short-term pulmonary health effects, particularly in
the severity of asthma attacks. Among particulate components, lead, alu-
minum and asbestos have been reported in indoor air at concentrations which
could result in increased blood levels (for lead), pulmonary effects (for
aluminum),.and mesothelioma (for asbestos). Cadmium and nicotine are among
other particulate products of tobacco smoke which have a potential for health
damage as components of the indoor air environment.
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The hydrocarbons are a diverse group including many pesticides,
propellants and solvents which may be present in indoor environments in
high short-term concentrations or in continuous lower-level concentrations
quite unlike typical ambient or occupational levels. Chemically, many of
these are halogenated hydrocarbons which have been implicated in liver
and respiratory system pathology, are neurotoxic, and have caused cancer
in animals. The vapors from one common solvent, methylene chloride,
metabolize to carbon monoxide in the human body resulting in elevated
carboxyhemoglobin levels. Pesticides may also contain organophosphates
which impact acutely upon the nervous system.
Smoking represents a special Indoor air pollution health hazard
through Its production of indoor air concentrations of carbon monoxide,
trace metals, nicotine and many other toxic, organic chemicals. The health
effects of tobacco smoke have been widely studied, although more in the
context of the active smoker than of the nonsmoking individual exposed
to smoke-contaminated air. Documentation of the health hazard of this
aspect of smoking 1s sparse.
The synerglstlc action of partlculates and SQ2 correlating with
an Increase 1n adverse health effects, seems to be well established.
Some evidence is available Implying a similar action among part1culate§,
N02 and oxldants. There is less evidence for other synerglstlc effects,
although studies available suggest an additive effect on lung cancer of
exposures to POM (polycyclic organic matter) from smoking, occupational
pollutants, and ambient pollutants.
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Several studies have investigated the contributions (individually
and in combination with various pollutants) of temperature and humidity.
The CHESS studies imply that the ambient pollutants contribute more to
aggravation of respiratory disease at higher temperatures. PAN (peroxy-
acetyl nitrate) appears to be more potent at higher temperatures. Another
study concluded that increasing the relative humidity of occupied spaces
reduced the relative incidence of respiratory conditions in school children.
Available information indicates that young children, the elderly,
and those with chronic respiratory problems are in general more sensitive
to irritant gases and particulates. Some asthmatics are particularly
sensitive to irritant gases and particulates. Anemics are theoretically
more susceptible to CO and N02» and persons with low cardiac reserve or
high COHb levels could also be jeopardized by ambient CO levels. Although
the factors in lead intake and balance are not well established, children
or workers who may already have a high lead blood level could possibly
achieve clinically important burdens from respiration of ambient lead
concentrations.
Research priorities in indoor air pollution ought to bear a
relation to the health hazards of the various pollutants. A ranking of
pollutants in terms of the hazards they present in the indoor environment
is conceptually possible, but its practicable realization is extremely
difficult.
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The health hazard from an indoor air pollutant is a function of
the following elements:
1. The levels at which it occurs indoors
2. The frequency with which it occurs indoors
3. The extent to which individuals are exposed to the pollutant
4. The exposure-response health effect of the pollutant
5. A judgement of the relative disbenefits to society of the
various possible health effects.
These elements are potentially quantifiable to society as a whole,
and from them a ranked order of the hazards of each indoor air pollutant could
be developed. Reliable data for Items 1 through 4 are difficult to obtain,
increasingly so as one goes down the list. Quantification of Item 5 must be
judgemental, probably arbitrary, and certainly controversial. The subject
is addressed, but not resolved, in Section 8.0 of this report.
Considering the concept of such a ranking, but without hard
numbers to support the conclusion, it may be suggested that the following
rough combined priorities, of health hazard and need for further research
into specific indoor air pollutant research, exist on the basis of present
knowledge of:
1. Carbon monoxide, nitrogen oxides and sulfur oxides
2. Tobacco smoke and its products
3. Chlorinated hydrocarbons and organophosphates in
pesticides
4. Fluorocarbons in propellents
5. Lead, cadmium, arsenic and aluminum.
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These air pollutants are listed in this order on the basis of
their ubiquity in nonworkplace indoor air environments, the extent to
which substantial health hazards have already been identified, and the
extent to which the existence of the hazard and current lack of data
suggests that further research is needed.
2.9 MODELING OF INDOOR AIR POLLUTION
Important objectives in studying indoor air pollution are to
obtain a better understanding of the potential health hazard and to
obtain information upon which methods for controlling indoor air pollution,
thus mitigating the health hazards, can be based. The achievement of
these objectives, even a partial achievement, requires the development
of models which can describe the interactions of indoor air pollution,
with the indoor environment and with people in that environment.
Useful models have two common attributes: they simplify complex
situations and they have a predictive capability. A model provides numeri-
cal relations between inputs (e.g., air pollution levels, human occupancy
habits, and structural characteristics of buildings) and outputs (e.g.,
air pollution exposures, health effects). No model is a perfect repre-
sentation of reality. Workable models of complex processes are highly
imperfect representations; their relative simplicity requires that this
be so. But they are considerably better for predicting outputs than
the alternative of guessing.
A complete mathematical model of the indoor air pollution
problem would enable a researcher, given appropriate input information
about air pollution sources and other factors, to calculate health hazards
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in any indoor environment. Some of the input data for that model would
be extremely difficult to obtain. With the present inadequate state of
knowledge of factors affecting indoor air pollution and human health, the
model's results would be of doubtful validity. The complexity of the
model, even with much necessary simplification, would probably make it
costly to operate. But despite these problems researchers have considered
It desirable to move toward developing such models. Models are one of
the keys to understanding and correcting the problems of Indoor air pollu-
tion.
A model with an output which quantifies the health hazard (or
health effect) of one or more air pollutants 1n an indoor, nonworkplace
environment should have the following classes of inputs:
Ambient outdoor air pollution
0 Climatology and meteorology
Building design and siting elements
Heating, ventilation and air conditioning characteristics
of the building
t Indoor air pollutant sources
Indoor/outdoor energy flow
0 Building occupancy characteristics, including personal
habits of the occupants
0 Mobility patterns of the occupants within the building
over time
0 Personal health status characteristics of the occupants
0 Toxicity of the pollutants, in terms of dose-response
0 Exposure and dosages of air pollutants experienced by the
occupants when away from the building.
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No such general model exists, although several efforts to design
indoor pollution exposure models, having much of this input, are now in
the planning stages. A large model of this kind could be created through
the joining together of less ambitious models which seek to describe and
quantify only a subset of the major elements.
The present report reviews the literature of analytical modeling
studies of indoor air pollution relationships. Specifically examined is
the state-of-the-art of definition of the following model parameters:
pollutant source strengths, decay rates, indoor environmental parameters,
structure identification parameters, and the impact of human activity.
Energy load and consumption models are reviewed briefly; these relate
building energy requirements to structural and HVAC considerations and
have no direct output which can be used to quantify indoor air pollution
concentrations. Three existing models which simulate building infiltration
and air movement within a building are described. Finally, five existing
Indoor/outdoor ventilation models with indoor air pollution calculation
capabilities are reviewed. These models are considered in the order of
their Increasing sophistication and capability. These models have many
common features and represent a consistent line of research development.
But at their best they are highly constrained procedures for calculating
gross Indoor air pollution concentrations in an idealized building. Much
more work 1s necessary to develop models which can reliably predict
pollutant concentrations 1n the complex environments of ordinary residences,
schools and public meeting places. No models now exist which can predict
air pollutant dosages and health hazards in such an environment.
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2.10 AREAS OF FURTHER RESEARCH INTEREST
The efforts to develop air pollutant hazard ranking models and
less ambitiously to develop indoor pollution concentration and exposure
models, are essentially efforts to characterize the indoor air pollution
problem as an integrated whole. The act of attempting to develop such
models has the highly valuable effect of demonstrating where important
knowledge gaps are. For an understanding and resolution of indoor air
pollution problems the information input for these models is needed,
even if the models themselves are never developed in the forms conceived
here.
On that basis priority areas for future research may include:
Further studies of the indoor source strengths,
concentrations, behavior and frequency of occurrence
of S02> CO, C02, NOX, sulfates, nitrates, halocarbons,
organophosphates and trace metals in a wide variety
of indoor environments
Occupancy and mobility studies of the ways in which
people use indoor environments, including studies
oriented toward susceptible population subgroups
Studies of the epidemiology of air pollution which
consider the totality of ambient, occupational and
indoor pollutant exposure
0 Air exchange patterns of buildings as functions of
structural and operational characteristics.
In the broad field of health effects of indoor air pollution
it is appropriate to consider a range of questions relating to the
absorption and clearance of pollutants in man and their health effects:
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Absorption and Clearance in Man
What is the Nature of Exposure? Since the absorbed
dose, and thus the biologic effect, will vary with
the exposure, it is necessary to characterize the
exposure as infrequent, intermittent, and persistent.
Since the exposure of different household members
(i.e., to the byproducts of gas used in cooking) is
varied, a method of assessing this characteristic
must be considered.
t What are the Pathways of Absorption? Multiple sources of
entry (skin, respiratory tract, eyes) may be pertinent
and from other media (food and water) than air.
What Early "Mechanical" Clearance Mechanisms Exist for the
Agent?Is the agent cleared by clljary action? Trapped
In the mucus of the upper respiratory tract? Swallowed
and excreted in feces?
How and to What Degree (Following Mechanical Clearance) is
the Agent Absorbed?While much valuable data has been
collected which directly relates the degree of exposure to
physiologic and pathologic effects, there is increasing
recognition that a better understanding of the absorbed
dose and its subsequent fate in the human is of great
Importance.
Following Absorption, What Clearance Mechanisms Exist?
The original agent may be converted to a more toxic product
or carcinogen within the body. In the clearance and meta-
bolism process, a number of different tissues may be
exposed and each may differ in sensitivity to the chemcial.
Interpretation of dose-response must consider each type of
tissue affected. This is particularly Important in evaluat-
ing low-dose, chronic exposure and its consequences. In
addition to carcinogenesis and mutagenesis, other questions,
such as whether autoimmune disease results from continuous
exposure to concentrations which produce no observable acute
effects, must be considered.
t Following Clearance, Is there Significant Deposition of the
Agent in Human Tissue? Where? What Is the Expected Dose-
Body Burden?The agent's deposition in tissue is clearly
of great significance. For example, asbestos fibers of
appropriate size which lodge in the lung, cause clear-cut
pulmonary disease. The site of the carcinogenic process is
determined by:
- The physical and chemical properties of the agent
- The type of contact with the host
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- The mode of clearance
- The fixation in particular organs - in general the
the carcinoma arises at those sites where the
carcinogen has the most prolonged and intense
contact with the tissues.
The investigator must also consider other factors such
as: Will the current exposure add to the existing body
burden of the agent and other substances which may be
byproducts of the clearance process? Does the agent
inhibit the clearance mechanism of a second pollutant
and thus increase the letter's body burden?
Human Health Effects
What Is the Direct (Immediate) Physiologic Response of
Tissues Exposed to the Agent In Varying Dosages?
Lachrymatlon, respiratory Irritation?
What Effects Occur Due to the Clearance Mechanism? Are
clearance byproducts carcinogenic, or do they cause other
types of adverse physiologic or pathologic response?
What Effects are Related to the Deposition of the Agent
In the Tissues? At What Body Burden?
What Synergistic or Additive Effects are Known to Occur
Between the Agent and Other Exogenous Agents In the Human?
The synerglstic action of particulates and SOg seems to
be well established. Some evidence implies a similar
synergism between particulates, N0£ and oxidants.
Is there Specific Group Susceptibility to the Agent?
These examples of areas for future research directions are drawn
from the appraisals made as the literature of indoor air pollution was
reviewed for this report. Other specific suggestions appear in the
detailed text which follows.
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Section 3.0
SOURCES OF INDOOR AIR POLLUTANTS
Air pollution in the indoor environment (e.g., in dwellings,
schools, public buildings and vehicles) originates from two categories of
sources; (1) air pollution in outdoor ambient air which enters the indoor
environment through ventilation and infiltration, and (2) air pollution
which is generated indoors. As research subsequently cited in this report
will show, some indoor air pollutants originate in significant quantities
in both categories, carbon monoxide for example; some appear in the indoor
environment in significant measure only from outdoor sources, PAN (peroxy-
acetyl nitrate) is an example; while others arise primarily from indoor
generation, as in the case of the fluorocarbpns used as propel1 ants in aero-
sol spray products. Discussions of the sources of these and other pollutants,
with appropriate literature references, are presented in the following
pages. The review of research literature is presented in two categories,
pollutants of outdoor origin and pollutants of indoor origin.
3.1 OUTDOOR AMBIENT AIR AS A SOURCE OF INDOOR AIR POLLUTION
The phrase "pollutant source" refers to both the place and the
mechanism through which the pollutant enters the environment. Sources are
normally described in terms of locations and source strengths (i.e., rates
of pollutant emission). In the study of indoor air pollution this pro-
cedure for characterizing sources applies well to indoor-generated pollu-
tants. It presents problems in discussing sources of outdoor-generated
pollutants. The original sources of such pollutants may be far from the
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indoor environment of concern; e.g., sulfur dioxide from distant power
plants, or photochemical oxidants arising in the open atmosphere impacted
by automobile emissions.
The original source of an outdoor-generated pollutant is often
beyond the scope of interest of indoor air pollution research. The
researcher looks upon the ambient air as it enters the building as the
proximate "source" of pollution. From the standpoint of an observer in
a building, the sources of outdoor-generated pollution experienced within
the building are the windows, doors, ventilation system intake ducts, and
areas of unplanned leakage in the building envelope. In the discussion
of outdoor-generated pollutants which follows, it is assumed that the
effective "source" of the pollutant is the mechanism (ventilation or
infiltration) through which the pollutant enters the building. The pres-
ence of outdoor pollutants within buildings has often been examined, in
scientific research, in terms of the relation between indoor and outdoor
pollutant concentrations. The definition of an "emission rate" at the
point of entrance into the building has not often been attempted.
Two important reports of a previous literature search [65, 283]*
prepared by Benson, Henderson, and Caldwell of EPA in 1972 and 1973, con-
cluded on the basis of a broad literature review that, "except for bacteria
and perhaps for fungus spores, indoor pollution levels appear to be con-
trolled primarily by outdoor concentrations." The review did not neglect
the role played by indoor pollutant generation; its broad conclusion refers
The numbers in square brackets, here and on all following pages, refer to the bibliography in
Appendix B. References are listed there in an order which is alphabetical and numerical.
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to the dominant role of outdoor pollution as evidenced in the scientific
literature available at that time. Benson et al. noted that many other
factors influence indoor air pollution levels, among them internal activ-
ities and pollutant generation, atmospheric conditions and ventilation,
time, location, type of building and air conditioning and filtration sys-
tems. They found that relative indoor concentrations of pollen and
reactive gases decrease with increasing outdoor concentrations, and that
the same effect can be observed, with less certainty, for particulates
and non-reactive gases; but they cautioned against assuming indoor con-
centrations of these latter to be less than outdoor concentrations. Their
conclusions were that the indoor-outdoor relationships are far from simple
and that the amount of reliable and readily comparable data upon which to
make generalizations is highly limited [65, 283].
The present document owes a large debt to the work of Benson and
his associates. Their work has been drawn upon heavily. In general, where
they have covered a subject in detail, the treatment here is very brief.
The present document provides detail in indoor-outdoor air pollutant source
and behavior research principally upon work reported after 1972 and hence.
not covered in their review. The reader is referred to the work of Benson
and his associates for detailed discussions of work covered there.
There have been subsequent overviews of the indoor-outdoor air
pollution problem, a major recent one being an Arthur D. Little report in
1975 on the environmental impacts of the new American Society of Heating
and Refrigeration Engineers Standard 90-75 for energy conservation in new
building design [44]. The Arthur D. Little report reconfirms the accepted
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view that outdoor air quality is a primary determinant of indoor air
quality. One result of this general view of the indoor air pollution
problem appears to have been that outdoor-generated pollutants have
received the most study in indoor air quality research. Another result
has been a continuing emphasis upon studies of indoor-outdoor pollutant
concentration ratios.
A review of research into the outdoor-generated component of
indoor air pollution follows, categorized by major pollutant species.
3.1.1 Sulfur Dioxide and Sul fates
Sulfur dioxide (SOg) has been widely studied in indoor environ-
ments, as described in the following pages. No reports were found of
studies in which sulfate concentrations have been measured in an indoor,
nonworkplace environment.
The literature indicates that indoor Sf^ concentrations are
primarily the result of the introduction of outdoor-generated SO,, into
buildings. There are few literature references to indoor generation of
SOg, although it has been demonstrated to occur in heating systems burning
coal or oil [715, 69] and from gas stoves [308].
Typically, indoor concentrations of SOp are found to be a function
of the SOg concentrations occurring outdoors, with the indoor concentrations
generally lower than the outdoor concentration [65]. Two factors were
reported as having a primary effect in producing lower concentrations of
S02 indoors [65]. First, S02 is reactive and may be differentially
absorbed by the interior walls, ceilings, floors, and their interior
surfaces and finishes [704, 113, 590, 588, 591, 589, 250]. Second, the
-34-
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rapid rise and fall which characterizes outdoor peak concentrations of
SOp are not reflected in similarly high, acute indoor S02 concentrations
[492]. This reduction of peak values is the result of the mixing of
outdoor air with indoor air as the peak S02 levels enter the building
and diffuse within it.
In their 1972 literature review Benson, Henderson and Caldwell
state that indoor S02 concentrations are roughly equivalent to outdoor
concentrations when the latter are low. As outdoor S02 concentrations
rise toward 20 pphm indoor S02 concentrations rise at a lower rate,
reaching only about 50 percent of outdoor levels. When outdoor S02 con-
centrations rise above 20 pphm, the indoor-outdoor concentration ratio
becomes still lower, with indoor concentrations being only about 30 per-
cent of outdoor levels [65]. Many investigations have confirmed the
general conclusion that when outdoor S02 concentrations rise indoor
concentrations rise also, but at a slower rate and to lower maximum
levels.
A series of investigations, beginning in 1958 and continuing
to 1976, which demonstrate this are listed in Appendix B [492, 359, 69,
694, 681, 680, 433, 478, 243, 670, 712, 27, 308]. Table 1, adapted
from a similar table prepared by Anderson in 1972 [27], displays the
results of these investigators' findings of indoor-outdoor ratios. The
table offers a convenient comparison among findings of various researchers,
but care must be taken in interpreting results from such a display. Indoor-
outdoor ratios of S02 may be expected to vary with the type of building
and with its climatological exposure as well as with the absolute levels
-35-
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of ambient outdoor S02 outside the building. It would be desirable in
such a table to stipulate absolute values of the concentrations, expressed
in terms of a common, standard averaging period for measurements (24 hours
for example) to permit verification of the conclusion, by Benson et al. [65],
that the ratio drops with higher outdoor concentrations. Differences in
room sizes, building materials, fixtures, furniture, ventilation rates,
and occupancy.probably also account for the differences among indoor-outdoor
ratios found by investigators [27]. Of the studies made prior to 1973, only
two measured ventilation rates [694, 415].
Anderson's own work in Arhus, Denmark in 1969 and 1970 [27],
cited in Table 1, is illustrative as an example of indoor-outdoor S02
ratio studies. In this work the presence of S02 was demonstrated in
100.samples of outdoor air and 67 samples of indoor air. Sample values
below 20 pg/m (0.7 pphm) were omitted, when either indoor or outdoor
air concentrations below that level were recorded, yielding the 11 pairs
of simultaneous outdoor and indoor samples referred to in Figure 1. The
author felt that the location was not ideal for the experiment, and that
a higher outdoor pollution level would have been preferable for this
investigation. His linear regression analysis of the 11 samples gave a
coefficient of correlation r = 0.52 and a line of regression: y = 0.20x
+ 20.9.
-36-
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TABLE 1. AVERAGE INDOOR/OUTDOOR RATIOS OF SULFUR DIOXIDE (SO2)
AS MEASURED IN BUILDINGS BY VARIOUS INVESTIGATORS
Authors
Kruglikova
and Eflmora
Shephard et aL
Phair et aL
Weatherly
Bieisteker
etaL
Mima et aL
Padfield
Grafe
Wilson
Von Ubish
Yocom et aL
Anderson
Hollowell
etaL
Year of
Investigation
1954 - 1955
1956
1957
1960
1964
1965
1965
1965 - 1966
1968
1969
1969
1969 - 1970
1975
Country &
Town
U.S.S.R.
Moscow
U.S.A.
Cincinnati
U.S.A.
Cincinnati
Great Britain
London
Holland
Rotterdam
Japan
Tokyo
Great Britain
London
Germany
Hamburg
Great Britain
London
Sweden
Stockholm
U.S. A.
Hartford
Denmark
Arhus
U.S.A.
Berkeley
Albany,
Calif.
Indoor/
Outdoor
Ratio
0.48
<1.00
0.64
0.60
0.20
<1.00
0.40
0.20
.25 -1.00
0.60
<1.00
0.51
>1.00
No. of Days
with Paired
Samples
58
60
60
32
800
Not Stated
36
120
10
96
38
11
Sampling
Periods
24 h
6h
2 h
24 h
24 h
Not Stated
24 h
Continuous
Continuous
5 min.
24 h
Continuous
Notes: 1. Table has been reproduced (with minor emendations) from I. Anderson inAtmos. Environmental,
VoL 6, 275-278, 1972.
2. Citations for the original authors listed here appear in an attached bibliography.
-37-
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CO
1
S-
o
o
70
60
50
40
30
11 paired samples
30 40 50 60 70 80 90 100 110 120
Outdoor, ug ra"
Figure 1. Scatter diagram of relationship between simultaneous 24-hour averages of indoor and
...;" outdoor sulfur dioxide on one locality. The line of regression is shown as it appeared in the
original publication [27].
In another study of indoor-outdoor SOg levels, not recorded by
Anderson in Table 1, Arthur D. Little Inc. conducted a field measurement
program in air conditioned spaces in Boston and Cambridge, Massachusetts
[42, 43], The Arthur D. Little investigators, working in summer months,
found that the indoor S02 levels were only slightly less than outdoor
levels when the outside ambient air was between 3.5 to 5 pphm. As the
levels of S02 outdoors rose above 5 pphm, the indoor S02 concentrations
remained near their "normal" levels (normal was undefined by the author),
When the S02 concentration outdoors dropped below 3.5 pphm, the indoor
concentrations usually also dropped below 3.5 pphm. However, for one
period of several days, the outdoor concentrations were on the order of
4 pphm while concentrations indoors for similar averaging periods
were about 5 pphm. This was the only reported case in which indoor
concentrations were higher than outdoor, although the results were
-38-
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presented graphically and average concentrations were not given. During
the winter, when outside ambient. S02 levels were higher, the indoor-outdoor
ratio became lower as the outdoor S02 concentrations increased [65],
A study which specifically addressed seasonal and diurnal trends
in indoor-outdoor S02 concentration ratios was conducted in Hartford,
Connecticut in 1969 by TRC - The Research Corporation of New England [713].
Tables 2 and 3 were drawn from the TRC study. A Sign-X Model 604-13 con-
ductimetric St^ analyzer was used in this study. The four sampling points
were sampled sequentially on a 5-minute basis. The results show a wide
variation, with several surprising examples of indoor-outdoor SC^ ratios
substantially higher than 1. In the case of the houses shown in Table 3,
the high indoor concentrations were attributed to internal generation of
862 in a coal-fired furnace [714]. For the most part, the results of the
TRC study confirm A.D. Little's finding that indoor-outdoor SC^ concentra-
tion ratios are lower in winter than in summer.
TABIE 2. SUIFUR DIOXIDE SEASONAL AVERAGES (PPHM) AND DAY-NIGHT RATIOS AT FOUR
PUBLIC AND OFFICE BUIIDINGS IN HARTFORD, CONNECTICUT [713]
FALL:
Far Outside
Near Outside
Near Inside
Fat In Id*
Far Inside
Far Outside
WINTER:
Far Outside
Near Outside
Near Inside
Far Inside
Far Inside
Far Outside
LIBRARY
Day Night
0.4 1.3
1.0 1.9
1.0 2.2
1.2 2.7
3.0 2.08
6.3 7.6
6.6 7.8
6.1 7.7
6.0 7.3
0.9S 0.96
Rattol
Day/Night
0.31
0.53
0.45
0.44
0.83
0.8S
0.79
0.82
CITY HALL
Day Night
1.7 2.2
2.S 2.4
2.4 2.7
2.0 2.5
1.18 1.14
6.8 7. 1
7.2 7.4
6.1 S.7
5.8 5.6
0.85 0.79
Ratios
Day/Might
0.77
1.04
0.89
0.8O
O.96
0.97
1.07
f.04
100 CONSTITUTION PLAZA
Day Night
1.7 1.8
2.3 2.1
1.3 1.1
1.4 1.0
0.82 0.56
5.2 5.2
5.0 5.8
4.0 4.3
3.9 4.0
0.75 0.77
Ratios
Day/Night
0.94
1.10
1.18
1.40
1.00
0.85
0.93
0.98
250 CONSTITUTION PLAZA
Day Night
0.3 2
0.1 2
-0.2 -0.1
-0.4 -0.1
-
4.5 3.7
4.7 4.1
3.9 3.5
3.8 3.7
0.84 1.00
Ratios
Day/Night
1.5
0.5
-
1.22
1.15
1.11
1.03
Note: Average concentrations of SO2 are stated in pphm and are derived as averages of a series of
24 hour SO readings taken throughout the Fall and Winter seasons, respectively.
-39-
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TABLE 3. SULFUR DIOXIDE SEASONAL AVERAGES (PPHM) AND DAY-NIGHT RATIOS AT
TWO HOUSES IN HARTFORD, CONNECTICUT [713]
SUMMER:
FarOntddc
NMT Outride
Nculnitd*
Fulnild*
F«Tlnitd«
FatOotrtde
FALL:
FuOuadd*
N«uOottid«
Nuzliald*
Fulatfde
Fubulde
FuOattlde
WD4TER<
FuOnnid*
NcnOmld*
Ncsrbfide
FIT Inside
FirlMlda
FaiOnadde
BlimSt.
Day Night
0.6 0.3
0.9 0.3
1.7 0.4
1.5 0.5
2.5 1.67
3.5 4.0
3.5 3.9
2.3 2.8
1.9 2.5
Ratio*
Day/Night
2
3
4.2S
" 3.0
0.88
0.90
0.82
0.76
0.54 a 62
1.3 2.1
1.3 2.2
1.1 1.6
1.0 1.7
0. 77 0. 81
0.62
0.59
0.69
0.59
CanollRd.
Day Night
0.0 0.3
0.8 1.0
3.3 2,6
3.8 2.8
9.3
2.2 2.4
2.4 2.4
2.1 0.2
2.0 0.6
RtOot
Day/Night
0
0.8
1.27
1.36
0.92
1.00
10. S
3.3
0.91 0.25
1.3 1.7
1.3 1.9
0.8 0.4
0.6 0.1
0.45 0.06
0.76
0.68
2.0
6.0
As noted, the high S02 levels in the Blinn Street residence,
shown in Table 3, were attributed by Yocom to S02 generation in a furnace
in the building. This, and other references to indoor generation of S02,
will be returned to later in this report under the headings of Section 3.2,
Indoor-Generated Pollutants and Section 4.0, Distribution and Behavior
of Indoor Air Pollution.
A useful study of the contribution of outdoor ambient S0£ to
indoor air pollution is included in research recently reported by the
Lawrence Berkeley Laboratory [308] in which a survey was conducted of six
homes with gas and electric cooling and gas heating appliances, in order
-40-
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to characterize the indoor air quality and determine the level of gaseous
and aerosol air pollutants from typical indoor combustion sources. Field
measurements of SOp were made continuously both indoors and outdoors using
a Thermo Electron 43 instrument which monitors S0« by UV fluorescence.
Results are discussed subsequently in Section 3.2 under Indoor Generation
of A1r Pollution.
3.1.2 Carbon Monoxide
The literature review conducted in 1972 by Benson and his associates
concluded that carbon monoxide (CO) concentration levels appear to follow a
pattern similar to S02 concentrations [65]. Indoor concentrations of CO
ranged from 80 to 100 percent of outdoor concentrations when outdoor concen-
trations were below 10 ppm. They ranged from 60 to 80 percent of outdoor con-
centrations when outdoor concentrations were above 10 ppm. The authors noted
that carbon monoxide is relatively unreactive. It should not behave like S02
by being absorbed on the surfaces of walls, ceilings, or floor coverings, and
its indoor concentrations should therefore approximate the outdoor concentra-
tions when monitored over a period of time. No explanations were suggested
by Benson and his associates for the observed reductions of indoor CO levels
below the outdoor levels.
One of the studies referenced by Benson and his associates was
performed in Hartford, Connecticut by Yocom, Clink and Cote [713]. Figure 2
and Table 4 display results of this study.
-41-
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8 Sight! 100 c**. «.
.2B5ht] Carroll Road
NAAQS for CO
(eight hour average
not more than once
per year)
Far Hear
outside outside
Near
Inside
Figure 2. Indoor/outdoor profile for winter CO data in Hartford, Connecticut. [713 ]
TABLE 4. SUMMARY OF CARBON MONOXIDE RESULTS, PPM (INDOOR/OUTDOOR RATIO, DIMENSIONLESS)
o«y
V
\
V
4.72
4.21
4. SO
4.S2
0.94
1.71
i.a
1.41
1.01
UM
2.04
2.41
2.41
1.2S
2.M
2.47
3.07
J.OS
1.04
1.21
1.21
1.17
3.41
UO1
2.70
2.71
2.fl
2.M
I. 01
4.32
1.20
5.22
S.2»
O.M
7.SO
.44
4. O2
4. O2
0.10
3.3*
3.SI
1.7*
1.12
l.U
4.24
1.21
i.a
0.74
2,01
2.11
2.11
2.11
1.07
1.14
l.M
2. O2
2.07
1.12
1.02
2.71
1.O2
3.04
1.01
1.71
1.41
1.41
1.41
O.M
2.0
2.74
1.22
1.25
1.21
2.43
2.17
2.12
2.14
O.M
2.0*
2.M
2.11
2.27
1.01
2.07
2.20
2.21
l.U
Note; These tables were reproduced from an article by Messrs. Yocom, Clink, and Cote published in the
Journal of the Air Pollution Control Association. Vol. 21, No. 5, 1971. Averaging times were not given
although the monitoring methodology is described. Five minute samples were directed sequentially to an
Intertech Intra-2 NDIR spectrophotometer. [713 ]
-42-
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In these observations the indoor-outdoor CO concentrations ratio
varies from a low value of 0.76 to a high value of 1.32, clustering around
unity. There is not a clear tendency for the value to be significantly
below unity.
Benson and his associates [65] cited indoor-outdoor CO con-
centration ratios obtained in living quarters in the vicinity of two
Russian industrial plants by Skvortsova [575] in which outdoor concentra-
tions were above 10 ppm and the corresponding indoor levels were sub-
stantially lower. Other studies of carbon monoxide impact on indoor
air quality arising from exterior sources of carbon monoxide, cited
by Benson and his associates, involved monitoring indoor levels of CO
in dwellings near known outdoor sources. Among these were studies by
Lamport [367] and Berdyev et al. [66]. These studies of indoor-outdoor
CO concentrations in circumstances of elevated outdoor CO levels generally
indicate that indoor CO levels do not increase as rapidly as outdoor
levels. The results are not conclusive and suggest a need for further
studies of indoor CO concentrations when outdoor CO levels are 100 ppm
or above.
Several studies have examined the special case of "air rights1'
buildings, in which buildings for residential and public use are constructed
directly over heavily travelled roadways. The question of carbon monoxide
pollution penetration into buildings - the carbon monoxide originating in
motor vehicle exhaust - becomes of special interest in this type of building.
One such study, involving measurement of indoor-outdoor air
quality and traffic relationships at two buildings in New York City, was
-43-
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conducted by the General Electric Company for EPA and published in
1972 [233]. Five Intertech NDIR CO instruments were used by the
General Electric team of investigators. High concentrations of ambient
carbon monoxide at three monitoring locations at one of the buildings,
referred to as the "air rights site," were expected since that building was
an air rights, high rise apartment dwelling straddling the heavily travelled,
multllane Cross-Bronx Expressway. The other building, referred to as
the "canyon site," was a similar high-rise apartment dwelling but was not
an air rights building; air quality measurements at the canyon site were
taken for control and comparison.
The General Electric Company investigators concluded that the
primary Influences on the outdoor-Indoor relationships of the four pollutants
monitored (i.e., carbon monoxide, hydrocarbon, total partlculates and
lead) were:
Traffic conditions
Nontraffic-related sources
Meteorological conditions
Site configuration.
Specifically for carbon monoxide concentrations observed, the General
Electric Company Investigators concluded:
t Carbon monoxide concentrations at all outdoor and
indoor locations result from automotive emissions
on roadways 1n the site vicinity.
On-roadway concentration levels Increase linearly
with Increase 1n traffic flow rate and decrease with
traffic velocity.
-44-
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CO concentration gradients across a roadway vary as
a function of traffic conditions in all lanes of the
road and the wind conditions close to the road.
t CO concentration gradients from a roadway to a
building vary as a function of the horizontal dis-
tance and the road level wind direction between
the high volume traffic lanes and the building.
winds from the high volume lanes to the building
increase concentrations at the building.
Average CO concentrations at the base of the building
vary directly with average concentrations of CO on
the roadway but are lower in proportion to increases
in horizontal and vertical distances from road
level. These distances create finite response
time lags at the building to changes in traffic
concentrations which vary as a function of road
level wind speed, direction and turbulence,
t There is an appreciable reduction in both peak and
average carbon monoxide levels between "on-roadway"
locations and adjacent buildings at the air rights
site, but not at the canyon site. As a result there
is no significant difference in CO levels along the
outside walls and inside the two structures.
Concentrations indoors at the building base in both
buildings vary with outdoor concentrations. Indoor
concentrations lag changes in outdoor CO levels.
It is suspected that this time delay is a function
of both wind conditions as seen at the building and
the direction of change in outdoor concentrations.
t Average concentrations inside and outside the buildings
reduce exponentially with height above ground level.
The rate of change with height outdoors is essentially
the same in the heating and nonheating seasons. However,
Indoors the decay in average concentrations with height
is greater during the nonheating season than during
the heating season. This variation is the result of
changes in the roof wind angle from the nonheating to
the heating season.
0 Indoor concentrations normally are lower than outdoor
concentrations at all heights above the roadway when
outdoor concentrations are high. Conversely, indoor
concentrations are higher than outdoor concentrations
when outdoor concentrations are low [233].
-45-
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These nine conclusions offer explanations for variations in
Indoor-outdoor CO concentrations in terms of the four influences listed
previously, i.e., traffic conditions, nontraffic-related sources, meteoro-
logical conditions, and site configuration.
The TRC study by Yocom, Clink and Cote cited earlier [715]
produced similar results for a different air rights building. The
Hartford Public Library straddles a busy four-lane access road connect-
ing downtown Hartford with a major interstate highway. Indoor CO concentra-
tions at this library approximated near-outslde concentrations (i.e., CO
levels adjacent to outside walls of the structure) but were lower than
far-outside concentrations when the far-outs1de concentrations were high.
The terms near-inside, far-Inside, near-outside and far-outside refer to
sampling points close to or at some distance (unspecified) from the wall.
The studies cited above deal with CO as an outdoor-generated
pollutant. Other studies dealing with indoor CO pollution resulting from
Indoor generation (Incomplete combustion in gas stoves, for example) will
be described in Section 3.2, Indoor-Generated Pollutants.
3.1.3 Carbon Dioxide
Carbon dioxide (COg) is a normal constituent of the atmosphere
occurring 1n unpolluted ambient air in concentrations ranging from 310 to
330 ppm. Pollution of outdoor air with anthropogenic C02, resulting primarily
from combustion of fuels, may result in ambient C02 concentrations as high
as 700 ppm. Average background ambient C0» levels have risen over the
last 100 years, from about 290 to above 325 ppm [394]. There has been con-
cern over the yearly additions of C02 to global background concentrations
-46-
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because C02 in the atmosphere absorbs terrestrial long-wave radiation (heat
energy) and re-radiates it back to earth. The effect of an increased amount
of C02 in the atmosphere is to reduce the rate of cooling of the earth's
surface and, in theory, will lead to an increase in the earth's surface
temperature (greenhouse effect) [12].
Local ambient concentrations of C02 higher than background levels
are regularly produced as a result of the emission of C02 from industrial
combustion processes. High levels of C02 have thus been used as an indi-
cator of polluted air [557], but such concentrations, ranging up to 700 ppm,
do not appear to have been of concern as an outdoor pollutant infiltrating
into indoor environments. C02 is generated not only by a complete combustion
of carbonaceous fuels used in heating and cooking but also in human expira-
tion and smoking; it is therefore a commonly indoor-generated pollutant,
but a review of the literature suggests that its indoor source strengths
have been little studied.
Researchers have found that carbon dioxide concentrations in
enclosed spaces can be dramatically higher than in the ambient air.
Ishido [326] reported that concentrations in several types of office
buildings ranged from 1 to over 10 times outdoor levels. Further,
according to Ishido, a space of 10 cubic meters (m3) per person and a
recirculation rate of 30 m3/h.r are required to maintain C02 concentrations
below 0.1 percent in rooms where people are doing office work.
Other investigators have examined carbon dioxide concentrations
indoors, finding higher concentrations indoors than out [65]. Studies
have been made of carbon dioxide generation in submarines and space
craft [530, 479, 661].
-47-
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3.1.4 Nitrogen Oxides and Nitrates
Only within the last four years have there been investigations
of the indoor-outdoor relationships of the nitrogen oxides, NO and NOp.
Studies previous to 1972 of nitrogen oxides in the indoor environment were
stated by Benson and his associates to have been insufficient for identify-
ing the indoor-outdoor relationships [65]. No studies of nitrate forma-
tion in or entrance into nonworkplace environments were found in the
literature search for the present report.
As is the case with S02 and CO, the nitrogen oxides may be
generated outside the building or within it. Researchers have studied
both aspects of nitrogen oxides in buildings. The present discussion
focuses on outdoor sources but the two categories of sources cannot be
wholly separated. Additional information on indoor generation of nitrogen
oxides appears in Section 4.4.
The sparse literature of indoor-outdoor nitrogen oxide concentra-
tions does not show the pattern of reduced indoor levels found for S02
and CO in similar situations. For example, in a study conducted in Dushambe,
USSR, on the effect of motor vehicle exhaust gases on air quality in
dwellings, investigators found that concentrations of nitrogen oxides were
the same in the street as in the first and third stories of the houses
monitored nearby [66]. In another case comparisons made between indoor
and outdoor air at several locations in Tokyo including factories, business
machine rooms and offices yielded no significant differences between indoor
and outdoor N02 concentrations [433].
-48-
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In a study of indoor-generated pollutants by TRC at four private
residences in Hartford, NO and N02 were monitored at several locations
within the dwellings and outside them using a Bendix Chemiluminescent
NO/NOY Analyzer [143]. Unlike earlier studies in Hartford by the same
t\
group of investigators, indoor-outdoor ratios of monitored pollutants were
not reported, since the purpose of this more recent program was to investi-
gate the indoor generation of air pollutants. The authors stated no
general conclusions pertaining to the ratio of indoor and outdoor nitrogen
oxides concentrations except in discussions of results of each separate
dwelling. In general, however, nitrogen oxides concentrations were reported
to be lower outdoors than at all locations indoors owing to the presence
of an indoor nitrogen oxides source, the gas stove [143].
Derham [158] conducted an investigation of Indoor and outdoor
concentrations of nitrogen oxides in a building near Los Angeles. Although
the building was not close to any heavily travelled roads, the report
stated that "peak concentrations seemed to be related to 'rush hour1 traffic."
Results of this study were reported graphically for each monitored pollutant,
with concentrations by time of day for selected days. Further discussion
of the results and conclusions of this study will appear in Section 4.4
since the thrust of the work centered on the indoor behavior of this pollutant.
Thompson and others [627] monitored NO, N02 and oxidants out-
side and inside 11 buildings in the South Coast Basin of California
during summer and fall seasons. Nitrogen oxides were grab sampled in
mylar bags and brought to a laboratory where they were monitored by "Atlas
electric devices, N02 - NOX analyzers." Concentrations of nitrogen oxides
-49-
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were found to be lower inside than outside although the indoor-outdoor
differences were less than with the more-reactive oxidants. Nitrogen oxide
levels inside elementary and high school classrooms without air condition-
ing were found to be essentially the same as levels of nitrogen oxides
outside the buildings.
The study of nitrogen oxide monitoring by the Lawrence Berkeley
Laboratory [308] will be discussed under Section 4.4 with indoor-generated
pollutants, since this was the thrust of that investigation.
3.1.5 Photochemical Oxidants
Photochemical oxidants are secondary pollutants formed 1n photo-
chemical smog from reactions involving hydrocarbons and oxides of nitrogen.
The principal component in this category is ozone (03) [557]. The presence
of significant amounts of ozone in the indoor environment is usually the
result of its Infiltration from the outside [439, 534, 627].
Indoor and outdoor concentrations of ozone were measured for
three air-conditioned offices in Boston and Cambridge during the 1968 air-
conditioning season by the Arthur D. Little Company. A follow-up study was
conducted during the heating season. In general, the investigators found
that ozone levels indoors were not much lower than those found outdoors.
The 03 levels were much less in the winter heating season, since 03 is
photochemically generated most strongly during the summer, but the
differences between indoor and outdoor concentrations were slight in
both seasons [42, 43]. These results are contrary to what might logi-
cally be expected to take place in the transfer of ozone to the Indoor
environment. Since 03 is a strong oxidizing agent reacting with other gasey
-50-
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(for example, with NO to form N02) reactions with NO and with various
materials within the building would have been expected to deplete the 0~
rapidly. Subsequent studies have validated these results for offices using
outside air for ventilation, but show variant results for other types of
buildings [627, 439, 534].
In a study conducted in 1971 by researchers at California Institute
of Technology [534] comparisons were made between the indoor and outdoor
03 levels 1n Pasadena, a city known for its high 03 concentrations. The
first purpose of the investigation was to monitor outdoor and indoor ozone
levels at a typical private residence and at two adjacent campus laboratory
and office buildings. Both campus buildings were air-conditioned but one
was supplied with 100 percent outside air while the other was supplied with
70 percent outside air and 30 percent recycled exhaust air. A second purpose
of the investigation was to investigate the mechanism through which ozone
decays. Measurements of the rate of ozone decomposition were recorded. Air
filters were tested with respect to their effectiveness in destroying ozone
and, finally, a theoretical model was developed to permit the correlation of
Indoor versus outdoor concentrations of ozone as a function of time [534].
Within the office building which utilized 100 percent outside air, peak
ozone concentration values were found to be about 80 percent +_ 10 percent of
the outside values monitored at an APCD (A1r Pollution Control District,
County of Los Angeles) station, located roughly 500 feet from the two
buildings. Within the adjacent office building, where 30 percent of the
air was recycled, the peak ozone levels were about 65 percent +_ 10 percent
i
of the peak outside levels measured at the APCD station. At the private
-51-
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residence the ventilation system was left off; windows were open and the
doors were opened periodically as persons entered and left the dwelling.
Instantaneous measurements of outdoor and indoor 03 concentrations indicated
that the maximum indoor concentrations of 03 were about 70 percent those
of the outside* and that these maxima lagged those of the outside by about
one hour. Further, the researchers found that the ozone level within a
home decreases at rather rapid rates once the doors and windows are closed
[534]. Specifics concerning mechanisms of ozone decay and the development
of a ventilation model for relating indoor-outdoor ozone concentrations will
be discussed later in this report under Section 4.0, Distribution and
Behavior of Indoor Air Pollutants and Section 9.0, Modeling of Indoor Air
Pollution respectively.
A group of investigators from Major Appliance Laboratories,
General Electric Company, conducted experiments on the decomposition rate
of ozone in several industrial facilities, an office and a home. Although
this study will be reported in more detail in Section 4.0, Distribution and
Behavior of Indoor Air Pollutants, it is worth noting here that the rate of
ozone decay was found to be dramatically altered by variations in humidity
or temperature and that the half-life of ozone in a typical bedroom was rather
short (6 minutes). The authors concluded that ozone decomposes rapidly after
it enters typical living spaces [439]. ,
In an independent study conducted in Cincinnati, investigators
concluded that ozone levels in a closed residence are significantly lower
than the normal range of outdoor ozone concentrations. Thompson [627]
attempted to determine the relationship between the concentrations of six
major pollutants (total oxidant, PAN, N02, NO, CO, and particulate matter)
-52-
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in the ambient air and the concentrations of those pollutants to which-people
were exposed in hospitals located in Riverside, California. Total oxidant
was monitored using a portable Mast ozone meter. Within specific struc-
tures, the relative concentration of total oxidant depended primarily upon
the rate at which it entered the building. Of the six pollutants studied,
ozone decomposed at the fastest rate [627].
3.1.6 Hydrocarbons
The outdoor-generated hydrocarbon of principal interest is the
total class of nonmethane hydrocarbons for which a National Ambient Air
Quality Standard has been established. There have been few studies of the
penetration of outdoor-generated hydrocarbons into indoor environments;
those which have been conducted, however, indicate that the indoor concen-
trations of hydrocarbons are directly proportional to the density of auto-
mobile traffic in proximity to the indoor locations [614, 233].
Hydrocarbons may enter a building as an outdoor-generated pol-
lutant (as implied by the studies cited above) or as an indoor-generated
pollutant from household chemicals, solvents, fuels and other consumer-
product sources. These indoor-generated categories will be considered in
Section 3.2.
Hydrocarbons and their derivatives are usually divided into two
broad classes: aliphatic hydrocarbons, the chained compounds and those
cyclic compounds which resemble the open-chain compounds; and aromatic
hydrocarbons, benzene and the compounds that resemble benzene in chemical
behavior. Polynuclear aromatic hydrocarbons are those hydrocarbons in
which two or more aromatic rings fuse and share a pair of carbon atoms.
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Polycyclic organic matter consists of compounds with two or more rings
that share two or more carbon atoms including aromatic hydrocarbons, cyclic
aliphatic compounds, and the aliphatic-aromatic compounds. All of these
may occur in the total class of nonmethane hydrocarbons and may enter
buildings as outdoor-generated pollutants. Given the task to produce a
background document on polycyclic organic matter pollution, a panel of the
National Academy of Sciences - National Research Council chose to divide
this broad area into two studies: Particulate Polycyclic Organic Matter
(POM) [459] and Vapor-Phase Organic Pollutants [460]. Since the latter
study was broad in scope 1n the sense that both cyclic and noncyclic com-
pounds were of concern, the document treated materials with low vapor
pressure and high molecular weight only briefly. Since these documents
are not in themselves original research, reports of studies described in
these documents which pertain to contamination of the indoor environment
required primary document assessment and are cited herein (when referred
to) under the .original investigations.
The contamination of indoor air with concentrations of poly-
nuclear aromatic hydrocarbons (PAH or PNA) may be the result of either
indoor generation, primarily smoking, or the infiltration of ambient air
which contains PAH. Bridbord et al. [87] reported Indoor concentrations
3
of benzo(a)pyrene (BAP) ranging from 0.0011 to 0.150 yg/m . BAP is an
Important constltutent of the polynuclear aromatics, 1s a known carcinogen,
and 1s often used as an Index compound for PAH concentrations. BAP con-
centrations in the ambient air are primarily the result of motor vehicle
emissions, heat and power generation, coke production and refuse burning
-54-
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[87]. Ambient levels of BAP have been found to range from 75-78 yg/m3
near bituminous paving operations (averaging times were unavailable) [87].
Data have been collected in office sites (with the absence of
tobacco smoke) that suggest that indoor air is 25-70 percent lower in POM
concentrations than air found in the immediate outdoor environment [459].
Detailed information on smoking behavior in these indoor spaces, however,
was unavailable.
Thompson [627] monitored PAN (peroxyacetyl nitrate, a chemically
reactive outdoor-generated member of the photochemical hydrocarbon complex)
using a PAN analyzer monitoring instrument in 11 buildings on the south
coast basin of California. The author found that PAN concentrations varied
in a similar fashion to those of ozone but that because of its greater
stability it persists inside structures much longer.
3.1.7 Particulates
Particulate matter has been measured both in the indoor and out-
door environments using a wide variety of techniques and is reported under
a number of names (e.g., total suspended particulate, particulate matter,
smoke, dust counts, inorganic and organic particulate, dirt, soiling index,
and resplrable particulate). The lack of standardization in research termi-
nology and technique makes it difficult to compare many of the important
results and conclusions of experiments undertaken to characterize particulate
indoor-outdoor relationships.
One study by Anderson [27], however, included a review of previous
indoor-outdoor particulate sampling, as shown in Table 5. In the work
cited by Anderson, it appears that when particulate measurements are taken
for one-hour averaging periods the ratio of indoor to outdoor concentrations
-55-
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of suspended participate matter is about 0.40 [564, 241]. Experiments
in which 24-hour samples were taken, however, reported indoor-outdoor ratios
of 0.80 to 0.95 [680, 478, 69], In his own experiment Anderson collected
150 paired samples of suspended particulate matter, measured simultaneously
at distances one meter inside and one meter outside a room in the technical
school of Arhus, Denmark. Figure 3 is a scatter diagram of the results of
his experiment. The correlation coefficient was 0.83 and his calculated
line of regression was y « 0.63 x + 5,9. In 69 percent of his paired
samples the indoor particulate concentrations were lower than the outdoor
concentrations. Anderson concluded that the reduction in suspended parti-
culate matter was presumably due to differences in the outdoor and indoor
settling, diffusion, and coagulation processes [27].
TABLE S. AVERAGE INDOOR/OUTDOOR RATIOS OF SUSPENDED PARTICULATE MATTER (SPM) [27]
U.J.A..
U.4.A..
-56-
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5O 6O 70 80 90 100 IIO 120
Figure 3. Scatter diagram of relationship between simultaneous 24-hour averages of Indoor and
outdoor suspended paniculate matter In one locality (the line of regression is shown [27].
Studies 1n Japan concluded that indoor suspended participate
levels are completely under the influence of outdoor changes [324, 325].
Thompson and his associates [627] stated that the greater part of the
large-sized particulate matter carried into schools and other buildings
in the South Coast Basin of California consists of soil particles
brought in on shoes.
In a study in Hartford, Connecticut, by Yocom and others,
investigators found that the daytime concentrations of particulate are
higher than nighttime levels by as much as 100 percent. The Hartford
group found that for offices and other public buildings, Indoor day-
night ratios are lower than outdoor day-night ratios in both summer and
winter, Another way of putting this is to say that the concentration of
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particulates in the air inside an office building does not drop relatively
as much at night as does the concentration of particulates in the immediately
adjacent outside air. For dwellings, the opposite was true. Particulate
levels within dwellings dropped relatively more at night than did the
particulate levels in adjacent outdoor air [65, 712].
The studies cited above have dealt with simple mass concentrations
of particulate matter per unit volume. These are of interest for indoor
air quality considerations, but it also of importance to study the size
distribution, other physical characteristics and chemical characteristics
of indoor air pollutants. Characterization of the size of suspended
particulate is important since the health hazard is related to the fraction
of particulate which can enter the human respiratory tract. Particles
larger than about 4 urn typically do not pass the nasopharyngeal portion
of the upper respiratory tract and are therefore of less health hazard.
Respirable particulates have been defined by the American Conference of
Governmental Industrial Hygienists [16] as those which pass through a
size selector with the following characteristics:
Aerodynamic Diameter Particles Passing Through
(unit density sphere) Size Selector
(ym) (Percent)
2.0 90
2.5 70
3.5 50
5.0 25
10.0 0
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In the course of the Hartford study of particulates an effort
was made to obtain an indication of the relative concentrations of both
respirable particulates and total suspended particulates, indoors and
outdoors, during the summer season. Unfortunately, however, the monitoring
methodology proposed was found to be unreliable by the investigators and
their sponsors and was therefore abandoned [713].
Concentrations of lead in the air and household dust were studied
in Omaha, Nebraska by Angle and Mclntire [33]. They reported lead levels
3
of up to 1.69 yg/m 1n a grade school located next to a battery fabrication
plant; lower levels were reported at urban and suburban high schools.
House dust lead concentrations were measured in urban and suburban homes
and day care centers. The urban samples ranged from 50 to 1200 yg/gm of
dust while the suburban samples ranged from 110 to 610 yg/gm [33]. Sayre
et al. [539] reported that lead in house dust may be higher than 5 yg/gm
and contribute significantly to the blood level of lead in children.
3.1.8 Other Outdoor-Generated Pollutants
Other outdoor-generated pollutants monitored with respect to indoor-
outdoor concentration ratios in nonworkplace environments were reported in
studies by Tomson and others of carbon disulfide and hydrogen sulfide [631],
monitored at a house near a viscose plant which discharged these gases into
the air; and "gaseous acids" as reported by Phair and others [492].
Studies of indoor-outdoor ratios of pollens and other biological aerosols
are found in the literature; these typically show, when the aerosols orginate
outside the building, that their concentrations indoors are at lower levels
than outdoors. Such studies have been more commonly performed for hospital
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and laboratory rather than residential environments [146, 595]. The non-
criteria pollutants (I.e., pollutants other than the six - SOp, CO, NOX,
oxldants, nonmethane hydrocarbons, and participates - for which National
Ambient Air Quality Standards have been set) have, however, been princi-
pally studied in indoor environments as indoor-generated pollutants.
3.2 INDOOR-GENERATED POLLUTANTS
The discussion of outdoor-generated pollutants in Section 3.1
was categorized by pollutant species, all pollutants having come effec-
tively from a single source - the outdoor ambient air. The discussion
of indoor-generated pollutants will be categorized by their sources in
the indoor environment: these are combustion, household cleaning and
maintenance, smoking, hobbies, aerosol spray products, and other sources.
3.2.1 Combustion
Two principal combustion sources of pollutants in buildings
are the heating plant and the stove. Other possible sources of com-
bustion-related pollutants are fireplaces, automobile operation in
attached garages, and candles.
3.2.1.1 Building Heating Plant Contributions
Building heating plants may be sources of CO, C02» NO, NOg
and SO, as well as particulates, any of which might be discharged
into indoor environments through faulty venting or operation of the
heating plant. Studies demonstrating the existence of such discharges
are rare.
-60-
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In a study conducted on 60 houses heated with oil, coal or
gas in Rotterdam, Netherlands, Biersteker and his associates concluded
that indoor S02 concentrations are not significantly affected by the
heating system used if the system is in good condition, but they reported
that indoor concentrations of SOp were 3.8 times the outdoor levels for
a 30 year-old home where a heater was believed to be faulty. They noted
that newer homes tend to have less sulfur dioxide in the living rooms
than older homes, and they concluded from their data that faulty
chimneys and heaters may play a bigger role in air pollution mortality
than has thus far been suspected [69], It was noted by Yocom and his
associates in their study of sulfur dioxide indoor-outdoor concentrations
at two houses in Hartford, Connecticut that a coal-fired furnace was the
probable source of indoor levels of S02 exceeding simultaneous outdoor
levels by a factor of as much as 2.5 [713]. In neither the Biersteker
nor the Yocom studies were any actual source strength measurements
attempted for the indoor pollution arising from heating plants.
In a recent study by the Lawrence Laboratory, elevated nitrogen
oxide levels were reported in a house equipped with a gas furnace [308],
but reports of NO and N02 levels associated with gas-fired heating plants
are rare; Benson and his associates found none in their 1972 literature
review. In this respect it is to be noted that Yocom et al. [716]
reported that gas heating systems did not appear to affect indoor CO
concentrations.
-61-
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The possibility that chrysotHe asbestos dust may be emitted
Into Indoor environments from rotary asbestos heat exchangers was cited
by Tonomura et al. [631] who reported concentrations from this source of
0.52 fibers/liter, well below a recommended maximum standard of 2 fibers/
liter.
3.2.1.2 Gas Stoves and Ovens
A comprehensive study of the impact of gas stoves on indoor
air quality was conducted by TRC in 1973 and 1974 [143]. The study
included two tasks:
Laboratory Study - measured emissions of NO, N02
and CO from normally used and operated gas
stoves in relation to several operating variables,
Concentrations on a mass basis were monitored in
a completely enclosed laboratory structure using
a stove selected as being representative. The
operating variables evaluated included air-fuel
ratios, flame intensity, time and temperature
and the use of ptlot lights.
Field Study - measured indoor and outdoor con-
centrations of NO, N02 and CO continuously over
two-week periods in four homes with gas stoves.
This study was conducted in Hartford, Connecticut
during two separate field measurement programs
during the spring-summer of 1973 and fall-winter
of 1973-1974. Three sampling points were located
indoors (one or two in the kitchen and either the
living room or bedroom) and one was located out-
doors. Data on stove use was recorded by the
homeowner.
Table 6 is a summary of the results of the laboratory program. For com-
parison, the authors included in the table emissions from a domestic gas
-62-
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TABLE 6. SUMMARY OF POLLUTANT EMISSIONS OF GAS APPLIANCES FOR SEVERAL
TYPICAL OPERATING CONDITIONS IN HARTFORD DWELLINGS [143]
Appliance
Older Gas Stove
with Cast Iron
Burners
Newer Gas Stove
with Pressed
Steel Burners
Unvented Space
Heater
Domestic Gas
Furnace*
Operation
Pilot Lights
1 Burner - High Flame
3 Burners - High Flame
Oven:
Transient
Steady-state
Broiler:
Transient
Steady-state
Pilot Lights
1 Burner - High Flame
3 Burners - High Flame
Oven:
Transient
Steady- state
Broiler:
Transient
Steady-state
Low Flame-Steady-state
High Flame-Steady-state
Heat Input
Rate
(Kcal/Hr)
150
2700
6780
2300
2200
3000
3800
100
3500
10200
4000
2200
4900
3700
2800
6200
Approx
30000
Pollutant Emission
Factors (yg/Kcal)
NO
45.3
92.6
117.0
157.0
91.4
137.0
88.8
4.7
130.0
138.0
331.0
77.9
126.0
136.0
76.4
135.0
N02
54.6
51.8
72.8
159.0
73.1
123.0
48.5
18.6
79.0
65.6
79.0
50.4
80.6
57.1
46.4
43.8
90.0
-co
419
382
475
1790
530
1350
818
842
510
315
1010
1620
846
757
632
319
36
Pollutant Emission Rates
mg/Hr
NO
6.8
250.0
793.0
361.0
201.0
411.0
337.0
0.5
455.0
1408.0
1324.0
171.0
617.0
503.0
214.0
837.0
N02
8.2
140.0
494.0
366.0
161.0
369.0
184.0
1.9
277.0
669.0
316.0
111.0
395.0
211.0
130.0
272.0
2700.0
CO
62.9
1031.0
3220.0
4117.0
1166.0
4050.0
3T08.0
84.2
1785.0
3213.0
4040.0
3564.0
4145.0
2800.0
1770.0
1978.0
1080.0
CO
I
* From Compilation of Ait Pollution Emission Factors (Revised), U.S. EPA, February 1972.
-------
furnace. From the laboratory study the authors concluded that:
The type of gas stoves tested emit significant
quantities of oxides of nitrogen and carbon
monoxides in the following ranges depending
upon stove operation:
NO = 90 - 130 yg/Kcal, 200-1000 mg/Hr
N02 =50-80 yg/Kcal, 100-500 mg/Hr
CO = 400 - 1000 yg/Kcal, 1000-4000 mg/Hr
Pollutant emissions from the newer stove were not con-
sistently higher or lower than the older stove for the
range of operations evaluated. The oven of the newer
stove did emit about three times more CO than the older
stove oven.
The different designs of the burners of the two stoves
did not appear to have consistent and reproducible
effects upon pollutant emissions. Tests designed to
evaluate the effect of air-fuel mixture upon burner opera-
tion Indicated that the best blue luminous flame was pro-
duced at an intermediate air shutter opening for each
stove. Variation in the shutter opening had little effect
on the pollutant emissions for the older stove but had
a greater effect on the newer stove. The Intermediate
air shutter opening (best flame) also had the highest
oxides of nitrogen levels for the newer stove.
Pilot lights, although using gas at a small rate, do con-
tribute quantities of pollutants comparable to those gene-
rated during cooking operations over a typical 24-hour
period because of their continuous nature. Pilot light
NO and N0~ emissions from the newer stove were less and CO
emissions higher than those from the older stove. The
newer stove also has a pilot light designed to use less
gas than the older stove.
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Evaluation of the number of burners in use and their flame
intensity showed that the emissions are similar for all
conditions when adjusted to an equivalent heat input basis.
Oven and broiler emissions are somewhat less than those for
the burners on the same heat input basis. An exception was
the larger amount of CO from the oven of the newer stove.
Total pollutant emissions per unit of time from a gas stove
are roughly proportional to the number and type of burners
used and the period of use [143].
The TRC group tested several representative types of utensils on
one burner of each stove. The types of utensils, flame settings and concen-
trations are shown in Table 7. The most substantial utensil effect apparent
1s higher CO concentrations from the use of the aluminum pot at low flame
conditions.
TABLE 7. POLLUTANT CONCENTRATIONS* RELATED TO VARIOUS UTENSILS
Test
ISA
18B
18C
18D
18E
19A
19B
19C
19D
19E
Operation
Condition
Low Flame:
High Flame:
Utensil
Aluminun
Cast lion
Stainless Steel
Fyrex
None
A himinum
Cast Iron
Stainless Steel
Pyrex
None
Stove
New
New
Pollutant Concentrations, jug/m^
NO
27
32
32
27
27
260
221
207
233
207
NO2
58
66
72
76
82
204
224
224
224
183
CO
1066
545
403
474
675
1910
1433
2380
2030
2030
The effect of utensils on pollutant generation was determined by measurement
of pollutant concentrations directly above the stove rather than by calculation
of pollutant quantities entering and leaving the laboratory enclosure [143 ].
-65-
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Based upon the findings of the field study the Hartford group
concluded:
Stove use and outdoor air quality both influence Indoor
air quality. This joint Influence 1s a function of house
permeability as determined by season. No evidence could
be found that stove and house age per se Influenced indoor
air quality. Except for CO in House No. 2, concentrations
of CO, NO and N02 are higher Indoors than outdoors.
The patterns of indoor air quality are influenced by Interior
design features. Kitchen concentrations are always higher
than other locations in the house where sampling takes
place.
Indoor N02 concentrations in the kitchens of most of the
houses are at concentrations which would exceed the National
Ambient A1r Quality Standard for N0« of 100 yg/m3 annual
average (if the concentrations were projected over one year.)
On several occasions, a concentration of 100 yg/m3 is
approached or exceeded throughout the house. In fact, aver-
age kitchen N02 concentrations for most sampling periods were
two to four times the outdoor NO,, concentrations.
t Indoor CO concentrations during the winter at House No. 3
and No. 4 approached the 8-hour average air quality standard
for CO of 10,000 yg/m3 (10 mg/m3 or 9 ppm).
The half life of CO, an extremely unreactive gas, was found
to be 2.1 hours in House No. 2 during an unoccupied period.
The half life for NO was 1.8 hours indicating its relatively
high stability in the indoor atmosphere. On the other hand,
N02 had a half-life of 0.6 hours indicating that in addition
to dispersion and dilution, NO? disappears through reaction,
absorption, or adsorption. This effect was noted in a quali-
tative way in several of the other houses.
§ Stove pilot lights were found to be a significant source of
N02 [143].
Findings by the Hartford group differ somewhat from findings of
Eaton and others at EPA [178]. This group, studying indoor air pollution in
a home using a gas stove, found significantly higher indoor kitchen concen-
trations of N02 than did the Hartford group. Eaton and his associates found
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peak values of N02 of 1 ppm (% 1880 yg/m ) with one-hour averages ranging
from 0.25 to 0.50 ppm (^ 470 to 940 yg/m ) when the kitchen was closed with
no ventilation; the gas flow was 0.204 ft /min, and the sampling intake
was 6 feet from the stove. Comparisons of indoor CO concentrations observed
by these two groups show more similarity, however, although the EPA group
found significantly lower CO concentrations. Most probably the difference
in CO concentrations may be explained by the difference in sampling distance
from the stove. The Hartford group sampled above the stove and "in the
kitchen, displaced somewhat from the stove" [308]. The difference in N02
concentrations would require more careful comparisons in technique, averag-
ing time and instrumentation for a valid comparison of results.
Most recently "pilot measurements" of S02, NO/N02/NOX> 03 and CO
were taken at various locations in and out of doors by a team of investiga-
tors from the Lawrence Berkeley Laboratory of the University of California.
Indoor measurements were taken in kitchens with the measurements being made
in the breathing zone approximately 1.5 meters above the floor near the
front of the stove [264]. Table 8 shows levels observed by this group in
three houses with the gas oven operating at 550° F for approximately 20 minutes,
TABLE 8. GASEOUS AIR POLLUTANTS OBSERVED IN HOMES WITH GAS OVENS
(OBSERVED LEVELS + 15%)
Home ID
Number
Ventilation
Conditions
CO (yg/m3)
NO (yg/m3)
N02 (ug/m3)
S02 (yg/m3)
2
No Duct
Fan Off
23,000
2,000
850
no
No Duct
Fan On
6,000
1,000
320
65
3
Duct
No Fan
2,000
500
150
<: 25
5
Duct
No Fan
7,000
150
95
-cl5
(reproduced from Hollowell et al. 1976 [308])
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The reference to "duct" 1n this table is to a duct leading from
the kitchen to the outside air - House Nos. 3 and 5 were equipped with
ducts of this kind, but had no kitchen exhaust fans. House No. 2 had no
kitchen duct but was equipped with a kitchen exhaust fan; tests were made
in House No. 2 with the fan on and with the fan off.
Table 9, also from Hollowell et al. [308], shows the effects upon
pollutant concentrations in the breathing zone under various conditions of
operations of the top burners of a gas stove. These researchers also found
a small increase in ozone levels during the use of an electric stove.
TABLE 9. EFFECT OF GAS BURNER CONDITIONS ON GASEOUS EMISSIONS
(OBSERVED LEVELS + 15%)
Identification
Number
2
3
4
5
Pollutant
CO
NO
N02
so2
CO
NO
N02
so2
CO
NO
N02
so2
CO
NO
N02
so2
Kitchen
Background
9,000
85
85
40
1,000
25
30
<15
3,000
55
60
<15
4,000
75
60
25
One Burner
On
No Grate
10,000
1,050
380
65
2,000
165
115
25
4,000
1,110
450
40
8,000
1,260
340
50
One Burner
On With
Grate
9.000
1,110
380
90
3,000
125
65
««
3,000
1,230
470
35
9,000
990
320
30
One Burner On
With Grate
and All Stain-
less Steel Pan
27,000
740
370
80
13,000
160
125
*15
3,000
680
380
25
8,000
640
265
25
(reproduced from Hollowell et al. [308])
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The purpose of these separate works was to measure the emissions
of gas-fired appliances and to test and propose methodologies for NO
A
.reduction.
Comparisons of the various studies of N0/N09/N0 and CO emissions
* A
and concentrations must be made with great care. While the different experi-
ments described here have carefully documented the various operating param-
eters which are controlled or allowed to vary in the respective studies,
each experiment used different sampling point locations, gas fired-appliances,
air-fuel ratios, and so forth. A more detailed examination of each of the
studies and their respective operating parameters must be made before com-
parative tables or graphs of experimental results may be made. One such
comparative task was displayed in a recent work by A.D. Little, Inc. and
is reproduced in Table 10 [44].
TABLE 10. GAS KITCHEN AND OUTDOOR CONCENTRATIONS OF NO2 AND CO
(Indoor, jug/m3 /Outdoor, ^ig/m3)
Reference
Ellcins (average of 51 summer
samples and 70 winter samples In
121 kitchens)
Elltins (average of 69 winter
samples in 69 kitchens)
Cote (average of 24-30 winter
days of monitoring in 3 kitchens)
N0?
(24-hour average)
148/68
108/58
87/40
CO
(8-hour average)
*
-
6000/2800
*One hour CO average of 57 winter samples in 57 kitchens during
cooking was 8100 ug/m3 t 7400 ug/m3.
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3.2.1.3 Candles With Lead Wire Core Wicks
The burning of candles with wicks containing lead wire cores will
contribute lead fumes and particulates to indoor air. Bridbord and Shy [85]
reported on both chamber and home experiments. In the chamber study, a
3
lead-wicked candle was burned in an 1.5 m chamber with an airflow of
0.54 m per hour. The level of lead in the chamber air was reported to
3
average about 850 yg/m for the four hours that the candle was burned.
The investigators found an average airborne lead concentration
3
of approximately 20 yg/m as a result of the burning of lead-wicked candles
in a home. As a result of these experiments the investigators concluded
that "... it would not be unreasonable to expect average indoor air lead
levels in the range of 10-20 yg/m3 as a result of regularly burning candles
with lead wire core wicks in the home" [85].
3.2.2 Household Cleaning and Maintenance
Household cleaning and maintenance can impact upon indoor air
quality through mechanical action and through the entrance Into the air
of cleaning and maintenance materials as pollutants themselves. In the
first category, mechanical action, household cleaning and maintenance -
remove some particulate matter from indoor surfaces which could otherwise
become later reentralned and airborne. But household cleaning and main-
tenance also put particulates (e.g., dust) into the air and may result
in the generation of gaseous pollutants (from solvents, for example) and
aerosol pollutants from the cleansers. As ati example of the adverse
mechanical Impact of cleaning, suspended participate matter concentrations
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Indoors by weight, as well as by particle counts, were shown by Annls
and Annis [34] in 1973 to increase during the just after vacuuming.
Manoharan et al. [411] found that 73 percent of the particles
In Indoor air were below one micron in size. These small particles are
transported by the air medium in which they are suspended (i.e., subject
to Brown1an movement, streamline flow, etc.). Sweeping, dusting, and
vacuuming can resuspend small particles held on the floor or carpet; in
vacuuming many of these small particles pass directly through the vacuum
bag.
Solvents and aerosols used in cleaning process are themselves
contaminants in the indoor environment. Their impact may be localized
to the specific rooms in which they are applied but, nevertheless, they
can enter the respiratory system during the process as evidenced by the
ability of the occupants to detect their odor. A detailed inventory of
the contents of common solvents and aerosols used for cleaning and the
exposures to building occupants of any of the active Ingredients has not
been studied in a substantive manner.
Cote and his associates in 1974 listed the active ingredients
for several household cleaning products. Furniture polish often contains
silicone, wax, and morpholine. Window cleaners often contain sodium nitrate,
Isopropyl alcohol, ethylene glycol, and ammonium hydroxide. Oven cleaners
contain relatively reactive species as evidenced by the ease in which
organic materials break down on the surfaces of ovens and stoves; some
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of the Ingredients are potassium hydroxide, hydroxyethyl cellulose, and
polyoxyelthylene fatty ethers [143].
Air fresheners are also a source of indoor gaseous contami-
nations through Introduction of substances to remove or mask household
odors. Fennelly [208] points out that particulates are involved to some
extent in odor transmission; they themselves are volatile, or may simply
serve as a transport medium for volatile matter. The reduction of particu-
lates has been shown to reduce odors from food preparation [641], It has
been found [74] that many air fresheners simply contain scents for which the
nose is more highly sensitive than it 1s to the undesirable odor, as well
as containing substances that reduce the nose's ability to detect odors.
It is by this mechanism that most air fresheners mask odors rather than by
reduction of particle counts, since large concentrations of spray or mist
would be required to cause small particulates to coalesce. Cote et al.
[143] report that the typical active ingredients of air fresheners consist
of propylene glycol, morpholine, and ethanol. Triisoprdpanolamine and
morpholine are often also contained in disinfectant sprays.
Solvents used 1n the cleaning process at schools and public
buildings often contain higher concentrations of more active Ingredients
than those used in the household. Exposures to these substances, however,
are usually localized and confined to cleaning personnel. Many dust mop
dressings and sprays, as well as floor waxes and furniture polishes, release
petroleum distillates during application. Hueper reported in 1962 that the
distillation products of petroleum have been recognized as carcinogens en the
skin and in the respiratory and alimentary systems. Further, many waxes and
polishes utilize either turpentine, chloroform or carbon tetrachloride as a
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base to keep the product 1n a liquid form. Hueper noted that fumes which
result from the evaporation of the base are chloroform and carbon tetrachloride
which have been shown to be potential carcinogens. The many common cleansers,
detergents, and scouring powders which use chlorine as a bleaching agent .
release fumes containing chlorine gas. The maximum allowable concentration of
chlorine gas for an eight-hour exposure in Industry is 1 ppm, the level at
which chlorine can be detected by smell is usually 1n the range of 3-4 ppm
[571]. In addition, the use of dlchlorobenzene compounds to mask odors
In toilet rooms results in Its release as a gas [571]. The use 1n cleaning
procedures of solvents which Include the aromatic, chlorinated and aliphatic
hydrocarbons, as well as esters, ketones, adds, and alkalis may present
a potential air pollution problem [403]. Blume has noted that the many
products which are commonly used to "cleanup," therefore, may actually
contribute significantly to the deterioration of the air 1n the Indoor
environment of schools and homes [74].
Building maintenance projects are often a source of indoor air
pollution. Sawing and sanding of wood introduce particulates (sawdust)
Into the air. Blume has reported that pine, birch, mahogany and beechwood
when used as Indoor paneling can elict allergic reactions in some individuals,
presumably from emanation of airborne allergens although Blume Is not
explicit about the transfer mechanism [74]. The use of asbestos or fiber-
glass Insulating or tiling materials can introduce asbestos and fiberglass
Into the air. The use of paint, varnish, shellac and lacquer introduces
contaminants in the air which affect not only the user but also occupants
of rooms freshly painted; the principal pollutant is the solvent [494],
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The polychlorinated blphenyls (PCB's), which are used as plastldzers 1n
some paints, may evaporate and be present In the air [353]. PCB's are also
used In varnishes and floor tile and, therefore, may present a similar
problem in this context [622]. The diphenyl mercury dodecenyl succinate
used in latex paint to prevent fungal growth can result in the release
of mercury vapor. The application of latex paint in rooms with poor cir-
culation can lead to mercury levels which exceed recommendations of the
American Conference of Governmental Industrial Hygienists (ACGIH) [570],
It was also found that the mercury vapors will remain in the air for a
considerable period, being present at 1000 times the ambient outdoor
levels 220 hours after application [570],
3.2.3 Smoking
The combustion of tobacco products is a source of air contamina-
tion which 1s solely a function of human habit and decision. The health
effects of tobacco smoke for the smoker have long been studied, but the
effects of tobacco smoke on Indoor air environment and upon non-smokers in
Indoor environments have only recently been the subject of Investigation.
The Inhalation of tobacco smoke involuntarily, by persons who are not actively
smoking, has been defined by Hoegg as passive smoking; this term 1s widely
used in current literature to describe the circumstance of breathing air
contaminated with tobacco smoke [531, 546, 132, 270].
Tobacco smoke contains a large number of chemicals. Stedman [601]
reported that "the number of compounds in the vapor particle phase exceeds
1,200" including: acids; alkanes; alkynes; alkenes; aldehydes; alcohols;
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alkaloids (one of which 1s nicotine); aromatic hydrocarbons; arsenic;
carbon dioxide; carbon monoxide; cadmium; carbohydrates; chromium; hydrogen
cyanide; esters, ketones; nitrogen dioxide; nitric oxide; nitric cyclic
ethers; oxygenated Isoprenoid compounds; phenols, phenolic ethers; polycyclic
hydrocarbons Including benzo(a)pyrene and benzanthracene; nickel; radio-
active constituents; steroles; sulfur compounds, and fat soluble and insoluble
particles of 'tar' [601, 351]. Tobacco smoke has also been found to contain
toxins which may be produced by bacteria and fungi present during the curing
and storage of tobacco [218, 578]. The smoker's exposure to these chemicals
results principally from mainstream smoke which is the smoke inhaled directly
Into the smoker's lungs. The sidestream smoke, which is not directly inhaled
during smoking, 1s the major tobacco smoke contributor to indoor air pollu-
tion, since 1t has been found to contain higher concentrations of tobacco
smoke components than the mainstream smoke [341, 675]. Kilburn reports that,
"sidestream smoke contains greater quantities of chloroform, extractable
tar, nicotine, pyrene and cadmium" [351]. Rylander found that sidestream
smoke contained almost double the amount of benzo(a)pyrene than mainstream
smoke [533].
A table displaying a comparison of the quantities of various com-
ponents of mainstream and sidestream cigarette smoke, based upon data from
Hoegg [303] and Corn [141] appears in the Health Consequences of Smoking
published by the U.S. Department of Health Education and Welfare in 1975
[657].
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Compound
General characteristics
Duration of smoke production
Tobacco burnt
Particulates, no. per cigarette
Particulate phase
Tar (chloroform extract)
Nicotine
Benzo( a)pyrene
Pyrene
Total phenols
Cadmium
Gases and vapors
Water
Mainstream
(mg/ciK)
20 sec
347 12
1. OS x 10
20.8
10.2
0.92
0.46
3. 5 x 10
13 x lO-5
0. 228
-5
12. 5 x 10
Sidestream
(mg/cig)
550 sec
411 12
3. 5 x 10
44.1
34.5
1.69
'27 .5
13. 5 x 10
39 x 10-5
0.603 _
-5
45x10
Ratio
Sidestream/
Mainstream
27
1.2
3.3
2.1
3.4
1.8
2.8
3.7
3.0
2.6
3.6
Comment
Filter Cig.
Filter Cig.
7.5
0.16
31.4
63.5
0.014
298
7.4
148
79.5
0.051
39.7
46
4.7
1.3
3.6
3. 5 mg of
Mainstream
and 5. 5 mg
of Sidestream
in partdculate
phase, rest
in vapor phase
Ammonia
Carbon monoxide
Carbon dioxide
Oxides of Nitrogen
The quantities shown in this table are estimated for a 35 ml
puff volume, 2 sec. puff duration, one puff per minute and 23 or 30 mm
butt length and 10 percent tobacco moisture.
Another table from an earlier HEW report on The Health Conse-
quences of Smoking, published in 1972 [653], provides lists of cigarette
smoke compounds which were judged to be probable or suspected contribu-
tors to the health hazards of smoking. Those lists were as follows:
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Compounds in cigarette smoke judged as probable contributors to
the health hazards of smoking.
Compound
Acrolein
Cresol (all isomers)
Hydrocyanic Acid
Nitric Oxide
Nitrogen Dioxide
Phenol
Acetaldehyde
Acetone
Acetonitrile
Acrylonitrile
Ammonia
Benzene
2, 3 -Butadiene
Butylamine
Carbon Dioxide
Crontononitrile
Dimethylamine
DDT
Endrin
Ethylamine
Formaldehyde ^
Furfural
Hydrogen Sulphide
Hydroquinone
Methacrolein
Methyl Alcohol
Methylamine
Nickel compounds
Pyridine
Concentration in
cigarette smoke
micrograms/ cigarette
45-140
68-97
100-400
0-600
0-10
9-202
180-1,440
88-650
140-200
10-15
60-330
12-100
43-200
3
23,100-78,300
4
10-11
0-0. 77
0.06
10-11
20-41
45-110
12-35
83
9-11
90-300
20-22
0-0. 58
25-218
Primary phase
classification
G-gas
P-particulate
G
P
G
G
G
P
G
G
G
G
G
G
G
P
G
G
P
P
P
G
G
P
G
P
G
G
G
P
P
In the document from which these lists were taken [653] there
were references to specific scientific investigations to support the
suggested health hazards involved.
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As the above lists show, the products of tobacco combustion
Include a wide range of gaseous and particulate contaminants. Tar and
nicotine are often selected from these as the substances used to charac-
terize the relative productions of toxic pollutants in smoking. Tar
refers to the amount of particulate produced corrected for water vapor.
Nicotine, an alkaloid, is the largest particulate product; it is known
to be highly toxic. Its presence in the air results only from the
combustion of tobacco and of related plant products; it is therefore a
useful indicator of the presence of tobacco combustion products in indoor
air pollution monitoring programs.
Studies of passive smoking have also used suspended particulate
matter (SPM), smoke, and carbon monoxide to characterize indoor contami-
nation. A more detailed treatment of tobacco smoke concentrations and
behavior is discussed 1n Section 4.0, Distribution and Behavior of Indoor
Air Pollutants.
3.2.4 Hobbles
The types and kinds of hobbles individuals pursue govern to a
large extent their potential indoor exposures to toxic air contaminants.
Many hobbies include activities involving toxic materials which, in an
occupational environment, would be controlled through protective measures
such as hood ventilation. These controls may be absent in the home
environment. This is particularly true of such activities as soldering
and furniture refinishing.
Painting in the home requires the use of a variety of solvents
and pigments, many of which are potentially quite hazardous. Oil paints,
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on varnishes, and resins (containing solvent bases consisting of aliphatic,
aromatic and halogenated hydrocarbons, alcohols, ketones and esters, or
mixtures of these categories of compounds) release toxic fumes during drying
processes (which Involve oxidation and polymerization reactions) [650].
Artists may use pigments in powder form which consist of very
fine dust 1n the resplrable particulate size range. These pigments con-
sist of a powdering base and a metallic element which utilize lead, arsenic,
antimony, cadmium, chromium, manganese, or mercury (to name a few) to give
the pigments their characteristic colors. Paint removers that contain
methylene chloride (also known as dichloromethane) can result in high con-
centrations of carboxyhemoglobin because of the rapid metabolization of
methylene chloride to carbon monoxide [610, 611]. Varnishes and wood stains
used in such hobbies as furniture refinishing contain various toxic
solvents such as turpentine and the esters and ketones used in lacquers.
The inhalation of silica dust, which can lead to silicosis [273, 50],
1s a potential hazard in ceramics and sculpturing. The inhalation of
fumes which result from the firing of pottery is hazardous because of the
presence of toxic metals, fluorine, chlorine, and sulfur dioxide gas.
The presence of asbestos in soapstone and serpentine is also a concern in
sculpture because of the potential for inhalation of asbestos dust
[273, 50]. McCann has noted that solder, used in hobbies such as the
making of leaded glass objects, can produce vapors containing cadmium.
Hobbles which Involves the use of plastics (acrylics, polyesters, epoxy
resins, polyurethanes, vinyl polymers, and polystyrenes) can also result
In exposure to toxic gases as they are heated to make them pliable. Some
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hobbles Involve using acrylic sheets and blocks while others use acrylic
glues and cements. The cements are either pure solvents like methylene
chloride, ethylene dichloride, and trichloroethane, or acrylic chips
which are dissolved in those solvents. The polyester resins which are
used in laminating consist of nontoxic polyesters dissolved in a styrene
monomer to which methyl ethyl ketone peroxide or benzoyl peroxide is
added. Epoxy resins produce large amounts of heat during the curing
process and can result in the production of toxic amine fumes from the
hardener. The highly toxic polyurethanes are made of isocyanate and
polyols and the spray foam and is considered too toxic for casual use,
although these products may be purchased at most hobby shops. The vinyl
polymers which include polyvinyl chloride and polyvinyl acetate can release
hydrogen chloride fumes. The cutting or sawing of polystyrene when heated
will produce methyl chloride gas, also highly toxic [403].
The various printmaking processes such as silk screening,
etching, lithography, and the photo techniques involved with each, as well
as photographic processing, involve exposure to air contaminants. The
solvents used in silk screening contain several toxic vapors such as
xylol, methyl ethyl ketone and acetates. The fumes from the nitric and
hydrochloric acids used in etching and lithography are also hazardous.
Photo techniques which require use of carbon arcs as a lighting source
produce carbon monoxide, nitrogen oxides, ozone, and toxic metal fumes.
The development of film requires the use of solutions which can give off
toxic vapors containing sodium hydroxide, sodium sulfite, formaldehyde
and chlorinated hydrocarbons. The fumes from acetic, hydrochloric, and
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chromic adds which are used In most photographic processes are also
hazardous. The result of the mixing of sodium sulflte and acetic acid,
commonly used 1n the photographic fixer, produces sulfur dioxide. If
the most common reducer, which contains potassium ferricyanide, is
exposed to heat or concentrated acids In a photo workshop, hydrogen
cyanide gas can be produced [403].
3.2.5 Aerosol Spray Products
Aerosol spray products, although varying widely 1n the chemical
nature of the pollutants they put into the indoor air, may be appropriately
considered as a general category of pollutant source because of their
quite similar source emission characteristics. Their periods of emission
are brief, are wholly controllable, and are the direct result of
conscious human activity within the building.
Cote et al. [143] conducted a survey of aerosol sprays used
among TRC employees and attempted to quantify them as a source of indoor
air contamination. They noted in their survey the usage rates, loca-
tion of use and the frequency of time of use of each aerosol spray product.
Most aerosol spray systems consist of a small amount of active ingredients
and a propel!ant. The active ingredients vary greatly in both concen-
tration and contents. Many of the substances used are highly toxic to
humans and are accompanied with specific directions and warnings to
control misuse. All sprays contain a propel!ant used to dispense the
functional or active portion from the container. It 1s estimated that
75 percent of the aerosol products contain one or more Freons as propel1ants
[143]. Freon is a DuPont tradename for various halogenated hydrocarbons.
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The halogenated hydrocarbons consist of one or more alkyl groups with
one or more attached halogens, usually chlorine and fluorine. Other
propellents are isobutane, propane, nitrous oxide, methylene chloride,
and (in the past) vinyl chloride. Selikoff and Hammond reported that when
vinyl chloride is used as a propel1ant it can lead to exposures that can
exceed 100 ppm [560]. The discovery of a high incidence of angiosarcoma
in workers who had been exposed to high concentrations of vinyl chloride
led to the elimination of vinyl chloride as a propellent in aerosol sprays
through an action of the Consumer Product Safety Commission in 1975. A list
of active ingredients in aerosol sprays was provided by Cote et al. [143]
and Frisch et al. [223]. Table 11 is a combination of these two lists.
In a report published in 1975, Gay [230] presented a similar
list of propel!ants in aerosol products, by product category, which included
the following:
Product Propel 1ants
classification used
Inhalants containing Freon 11 (trichloro-
bronchodilator drugs fluoromethane)
(11 products) Freon 12 (dichloro-
fluoromethane)
Freon 114 (dichloro-
tetraf1uoroethane)
Mouth products (6 Freon 12
products) Freon 114
Freon 1426 (mono-
chlorodi f1uoroethane)
Vaporizers (2 Products) Freon 11
Freon 12
Trichloroethane
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Product
classification
Propel!ants
used
Hair products (62
products)
Women's personal hygiene
products (22 products)
Deodorants and anti-
perspirants (38
products
Foot products (9
products)
Miscellaneous products
for personal use (18
products)
Freon 11
Freon 12
Freon 114
Freon 152a (difluoroethane)
Methylene chloride
Vinyl chloride
Propane
Isobutane
Freon 11
Freon 12
Freon 114
Isobutane
Freon 11
Freon 12
Freon 114
Freon 142b
Propane
Isobutane
Freon 11
Freon 12
Freon 114
Freon 11
Freon 12
Freon 114
Isobutane
Propane
Cote et al. [143] estimated emissions in the form of usage rates
for the specific households surveyed. Since the exact proportions of
propellants and active ingredients were proprietary information, data
were unavailable on the exposure of individuals to any of the active
Ingredients contained in the sprays. Table 12 describes the aerosol
usage patterns of persons surveyed in this study.
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TABLE 11. ACTIVE INGREDIENTS IN COMMON AEROSOL
SPRAY PRODUCT CLASSES [143,223]
Housekeeping Product!
Furniture Polish Dinitrobamene, l,l,l-aich)oroethane, patxolenm
dtaUlatea, dllcone, wuc morphoUne
Spot Remover PereUeroetfaylene
Oven Cleaner Sodfam hydroxide, hydruxyethyl cellulose, polyoxyethyt
fatty ether*
Drain Cleaner 1,1,1-tricUaroemaae, petroleum distillate*
Lysol O-phenylpheaol, N-alkyl-N-ethyl motpholtadum «thyl
raUates
dome 4-chloro-Z-cjrclopentylpbeiiol, nid«-Uiiiic
add amide
TUe Cleaner Tetracxttametfaylenadlaiiilne
Pre-wadi Treatment Perdilofoetirjrlene, peoalenm rfiftt>1«trt
Window Cleaner* Sodhnn nitrite, inpcopyl alcohol, etfayleae (lyool,
DUtaleetem S(«y» Trii»ot«op«iol»min« moxphoUae
Ab Fieihtinri Proplyleae glyeol morphoHne, ctbaool
PeaonalUte
Deodotut Spray Hyckated «h«
-------
TABLE 12. AEROSOL USAGE PATTERNS BY AEROSOL PRODUCT CATEGORY IN TRC HOUSEHOLDS [ 143 ]
Product Category
Deodorant Spray
Halt Spray
Shaving Foam
Air Fresheners
Disinfectant
Sprays
Furniture Polish
Sprays
Dust Sprays
Oven Cleaners
Percentage of
Households
Using this
Product
74
71
45
26
63
84
18
42
Frequency of Use
Once or Twice a
Day
3 times per week
Once a day
Once a week
3 times per
week
Once a week
Once a week
4 times per
year
Time of Use
Early Morning
Late Evening
Morning or
Evening
Morning or
Evening
Morning-
Afternoon
Morning-
Afternoon
Morning-
Afternoon
Morning-
Afternoon
Afternoon
Location of Use
Bathroom
Bathroom
Bathroom
Throughout
House
Kitchen,
Bathroom
Living Room,
Bedrooms,
Dining Room
Living Room,
Bedrooms,
Dining Room
Kitchen
Average Usage Rate
for Household
g/mo.
112-140
84-112
84-112
28-56
112
56
28-56
84
Weight Fractions
of Propellant
Percent
40
70
10
80
80
60
60
10
Propellant
Emission
Estimates
(g/use)
1.0-7.2
4.9-6.5
0.3-0.4
5.6-11.2
7.5
8.4
4.2-8.4
20-25
I
00
ui
i
-------
Gay et al. [230] in an investigation of the exposure to vinyl
chlorides, PVC's and other propel 1ants, conducted an experiment to deter-
mine concentrations of these substances over time. The results found
were as follows:
Concentration of propel1ant after 60-sec release
of hairspray and deodorants in 29,300 liter room.
Propellent concentration,
ppm
Sample
1
2
3
4
Time,min
Breathing zone
during spray
Vinyl
chloride
122.7
10
30
60
25.8
5.6
0.1
Freon 12
62.1
11.0
2.5
0.1
Concentration of propellent after-30-sec release
of insect spray in 21,400 liter room.
Propellent concentration,
ppm
Sample
1
2
3
4
5
Time, mi n
1
31
61
151
151
Vinyl
chloride
380.1
52.1
24.6
10.3
0.8
Freon 12
466.4
54.4
26.4
11.5
0.9
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3.2.6 Other Sources of Indoor-Generated Pollutants
3.2.6.1 Pesticides
Pesticides in the air are extremely hazardous because it is
thought that the body is able to absorb pesticides faster and in greater
quantities through the lungs than through either ingestion or skin
contact [558]. The pesticides which are used most frequently in the
indoor environment and therefore contribute the most to indoor air
pollution are insecticides. Household insecticides comprise a large
group of chemicals which number in the hundreds and include synthetic
organic, inorganic and botanical chemicals. The synthetic organic
chemicals contain the derivatives of chlorobenzene (i.e., DDT), indane (i.e.,
aldrin, dieldrin and chlordane, etc.), benzene hexachloride (i.e., Hndane),
chlorinated camphene (i.e., toxophene), phosphate esters (i.e., malathion) and
carbamates. The inorganic chemical-type insecticides use arsenic compounds,
fluorides, selenium etc., while the insecticides from botanical sources
include nicotine and pyrethrin [36], The following table illustrates the
many different types of active ingredients which are present in some of the
most common brand name household insecticides.
Insecticide Active Ingredient
Echols Roach Tablets Boric Acid
Hot Shot Roach and Ant Bug
Killer d-trans Allethim
Johnson's No Roach Malathion
Longlife Flea Killing Collars
for Dogs DDVP
Raid Ant and Roach Killer DDVP
Raid Flying Insect Killer Pyrethrins
Real Kill Insect Spray Pyrethrins
Shell Improved No-Pest Strip DDVP
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In some cases the Insecticide's effectiveness Is Increased by adding
chemicals such a N-octyl bicyclopeptene dlcarboxamlde which has a syner-
glstlc effect on the d-trans allethrin In Hot Shot Roach and Ant Bug
Killer [36]. Insecticides can cause problems associated with indoor
air pollution primarily by two ways, through respiratory contact during
use (e.g., aerosols) and through the inhalation of the products which result
from the insecticide's volatilization [71]. Some insecticides, e.g.,
lindane, chlordane and DDVP, remain in the environment for long periods of
time and may vaporize from surfaces long after application thereby releas-
ing harmful chemicals to the air [139]. Many household insecticides are
sold in aerosol cans, presenting health problems to the user during and
shortly after their use. No reports of quantitative investigations of the
pesticide persistence in the indoor air were identified in the literature
search. Most pesticide studies have been concerned with pesticide use
outdoors as monitored in soil and water.
The dispersion routes that pesticides take in the air have not yet
been defined [594, 333, 624]. Very little is known of the products which
result from the transformation of pesticides that takes place in the air
[556, 566].
3.2.6.2 Air Conditioning Systems
Air conditioning systems can be a source of air contaminants of
the Indoor environment. The pollutants Include biological aerosols, ozone,
and participates such as aluminum and asbestos dust. A1r conditioners
have been found to be a source of biological aerosols, that is, micro-
organisms have been found in and being distributed from air conditioners
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[52, 313]. It has also been reported that air conditioners contribute
to the levels of ozone 1n the Indoor environment [313]. The authors
just cited found that air conditioning systems have contributed to the
generation of dust containing asbestos from wall spaces, where asbestos
had been applied by spray, as an insulation material in the airducts of
air conditioning systems. The contamination of air by aluminum compounds
(hydrated aluminum oxide, chlorinated aluminum oxide, and carbonated
aluminum oxide) was reported by Buchnea and Buchnea [94] and Morton [313]
to result from the corrosion of the aluminum used in air conditioners.
3.2.6.3 Insulation Systems
Asbestos has been widely used in fabrics, insulation, ceiling
tile, and fireproofing [488]. Damage to and erosion of such materials in
buildings has been found to contribute to contamination of the air [467].
Asbestos dust was reported in air samples when spray-applied asbestos was
used to coat wall spaces [313]. Spackling, patching and taping compounds
used in some home repair work were found to contain asbestos and result
in the exposure to dangerous concentrations in the indoor air [525].
Although Tonomura [632] found a lack of significant air contamination
resulting from the use of asbestos in heat exchangers, Morton [313] points
out that only light microscopy was used; the conclusion was not definitive.
Rohl et al. [525] pointed out that light microscopy cannot allow for the
individual study of particles in the Sum range where the spackling, patch-
Ing and taping compound particles normally are.
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The study of asbestos contamination of air in public buildings
conducted by Nicholson and others [467] included the reporting of measure-
ments of asbestos fiber concentrations in the air in homes of asbestos
3
workers. Concentration levels between 100 and 5,000 yg/m were cited,
but no information was provided about the circumstances of the measurements.
3.2.6.4 Particle Board
Formaldehyde is introduced into the indoor air environment from
particle board, a building insulation and furniture material which is being
used more and more frequently. Andersen et al. [29] reported in 1974 that
formaldehyde concentrations in the air of 23 Danish homes ranged from 0.08
3
to 2.24 mg/m . It was found that the concentration of formaldehyde decreased
with the age of the house (the newest had the highest concentrations) and
with increases in ventilation rates.
3.2.6.5 Solvents
Indoor air concentrations of carbon tetrachloride have been measured
in houses (near a solvent recovery plant in Maryland) at between 10-45 ppm
while the outside ambient air contained 1 ppm [86]. The same investigator
prepared a tabulation of predicted concentration levels of halogenated
hydrocarbon solvents (a class of which carbon tetrachloride is a member),
which is as follows:
Predicted
indoor air
Solvent Temperature "C concentration, ppm
Trichloroethylene 20 80
Tetrachloroethylene 26 26
1,1,2-Tr1ch1oroethane 21 26
1,1,1 -Tri ch 1 oroethane 20 130
Carbon Tetrachloride 23 130
Methylene chloride 24 520
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The predicted indoor concentrations shown here are based upon
the assumption that the solvents reach 0.1 percent of saturation levels
[86], which is in effect an estimate of source strength.
Methylene chloride (dichloromethane) is a main ingredient in
many common household products. One of these products is paint removers
which are important because of an increase in home furniture refinishing.
Methylene chloride Is a very volatile substance which is metabolized upon
Inhalation to form COHb (carboxyhemoglobin). This can take place in
levels which are toxic. Stewart and Harke [612] reported indoor methylene
chloride levels with a maximum concentration of 1278 ppm.
3.3 AN OVERVIEW OF RESEARCH IN INDOOR AIR POLLUTION SOURCES
An overview of this subject suggests that much remains to be
learned about the quantitative levels of indoor air pollution source
strengths» both with respect to those pollutants which infiltrate (or
are ventilated) into buildings and with respect to pollutants generated
in the indoor environment. Studies of indoor-outdoor pollutant con-
centrations provide a surrogate for source strength measurements of
ambient pollutants entering a building from outdoors, and there are many
such studies for the common ambient pollutants, S02» CO, NOx, photochemical
oxidants, and TSP. The studies show that concentrations are typically (but
not always) lower indoors than outdoors, with the indoor-outdoor ratio being
lower for pollutants which react chemically with materials in the environment.
This effect says something about pollutant behavior indoors, but little
about the relative or absolute source strengths of ambient pollutants
entering buildings. Ventilation studies (to be discussed in Section 9.0,
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Modeling of Indoor Air Pollution and in Appendix A) are required to esti-
mate the quantities of ambient air pollutants introduced into buildings.
Indoor-generated pollutants arise from combustion in heating
systems and stoves, from household cleaning and maintenance, from smoking,
from hobbies, from the use of aerosol spray products, and from many other
sources. There has been considerable research into the combustion product
pollutants in the indoor environment, including measurements and calcula-
tions of actual source strengths. . Estimates of pollutant emissions have
been made for aerosol spray product propellants, and to some extent for the
airborne pollutant products of smoking. Emission rates for the active
ingredients of aerosol spray products have been difficult to estimate
because the nature of the ingredients is often proprietary information not
disclosed by manufacturers. Source strengths so far have been little
Investigated for emissions from diffuse sources such as cleaning, food
preparation, pesticide application, painting and hobby activities.
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Section 4.0
DISTRIBUTION AND BEHAVIOR OF INDOOR AIR POLLUTANTS
In Section 3.0 we discussed the sources of indoor air pollution*
identifying the causes of pollutant occurrence in buildings. The focus
of the discussion was upon points of origin (indoor-outdoor), source
strengths, and the observed indoor concentrations of the pollutants.
Much of the early research into indoor air pollution was con-
cerned with the relationships between outdoor pollutant levels and
indoor pollutant levels, the tacit assumption being that outdoor sources
of pollution were the important areas to consider. The research placed
emphasis on "indoor-outdoor" concentration ratios. Studies of indoor-
generated pollutants concentrated upon source strengths, and upon their
contributions to the indoor-outdoor ratios.
A now growing body of research addresses another aspect of
indoor air pollution, the dynamic behavior of the pollutant as it moves
in the building from its point of origin to its ultimate fate. Research
into the behavior of indoor air pollutants includes studies of their
airborne transport, diffusion, chemical transformation, deposition and
absorption. It is concerned with the spatial and temporal changes of
pollutant concentration and character within the building, and with
decay rates, residence times and the fate of pollutants.
The discussion which follows, based upon a review of the
existing literature of indoor air pollution research, necessarily draws
upon work already reviewed in Section 3.0, Sources of Indoor Air Pol-
lutants. There is overlap in the literature and data reviewed because
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past researchers have not separated source and behavior characteristics
of pollutants in their studies of indoor air pollution. An effort is
made In what follows to make that distinction.
In ambient, outdoor conditions, air pollutants are transported
and dispersed under the influences of wind speed, wind direction and
the turbulence in the atmosphere. Pollutants in the ambient air are
chemically transformed (if they are chemically reactive) through inter-
action with other airborne pollutants and through absorption and adsorp-
tion onto vegetation and other surfaces at ground levels; the rates at
which some of these processes take place in ambient conditions are
affected by temperature and humidity. The outdoor, ambient air pollu-
tion concentrations are thus a function not only of outdoor pollutant
source strengths but also of air transport, diffusion, and chemical
reactivity; all of which are influenced by ambient meteorology.
Indoor air pollution concentrations are also functions of
pollutant source strengths (whether due to infiltration of polluted
outdoor air or indoor generation of pollutants) and of air transport,
diffusion and chemical reactivity occurring within buildings. The
chemical reactivity and the internal air flow are both affected by
temperature, and the reactivity may be affected by humidity as well.
In the outdoor environment the meteorological processes which
affect air pollution concentrations occur on a large scale and cannot -
in general - be controlled or altered significantly for air pollution
control purposes by human efforts.
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In the indoor environment the air movement and other elements
of indoor climatology which affect indoor air pollution concentrations
depend only in part upon outdoor conditions. They are also functions
of building design, heating, ventilating and air conditioning system
operation, and building use and occupancy. The mechanisms by which
indoor air flows and indoor temperature and humidity (building clima-
tology) are determined are discussed in detail in Sections 7.0 and 9.0
of this report, to which the reader is referred. They will not be
discussed here. The distribution and behavior of pollutants indoors,
as observed by various researchers and reported in the scientific lit-
erature, are discussed below. The discussions are categorized by types
of pollutants.
4.1 SOo AND SULFATES
As discussed in Section 3.0, Sources of Indoor Pollutants,
there are few indoor sources of sulfur dioxide, although in some cases
SOp emissions have been attributed to faulty heating plants in buildings
and dwellings fueled by oil or coal [69, 713]. Investigations of
indoor SOg behavior have characteristically begun with consideration
of an indoor-outdoor S02 concentration relationship. The residence
time and fate of S02 in the indoor environment have typically been
investigated in the context of these indoor-outdoor concentration
studies.
To the extent that the concentration of S02 inside a building
is a function of the ambient concentration of S02 outside the building
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it is also a function, in part, of the emission of S02 from outdoor
sources in the upwind environs of the building. Outdoor source emis-
sions of S02 are dependent largely on the sulfur contents of fuel used
for power generation and heating and upon the quantities of fuel used.
Outdoor emissions of S02 tend to be highest during the heating season
in locations where the winters are colder, and highest in the cooling
season in locations where the summers are warmer [39, 40].
Researchers have found indoor S02 levels to be generally
(although not always) lower than outdoor concentrations [69, 397, 359,
694, 680, 42, 43, 433, 478, 243, 712, 670, 27, 65, 308].
Benson and his associates identified two factors as probable
principal causes for the observed reduction of S02 concentration levels
in the indoor environment [65]. First, S02 is a chemically reactive
species and is adsorbed by walls and other interior surfaces; second,
the frequently sharp and brief outdoor peak concentrations of S02 may
be reduced by the lag time of transport into the building through narrow
or small inlets and the relatively slower diffusion rates indoors where
the turbulence characteristic of ambient outdoor air is lacking. Because
of these factors the outdoor concentration peaks, frequently sharp and
of short duration, are spread out and flattened when they reach the
indoor environment [492].
Findings by Biersteker et al. [69] in Rotterdam homes and
Yocom et al. [716] in a home in Hartford, Connecticut support a con-
clusion that the principal source of S02 in houses may be faulty
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heating system operations. Of two coal-fired houses sampled in the
Hartford study, one was found to have significantly high indoor S02
concentrations. In this house the Indoor SOp concentrations were com-
pletely dominated by this Indoor source with peaks roughly coinciding
with furnace stoking periods. The indoor concentrations over time were
presented and shown to be much higher than those recorded outdoors [716].
In the Rotterdam study of indoor air pollution, only one home
was found to have continuously higher S0« concentrations indoors than
outdoors. In another, Intermittently higher concentrations of S02 were
found Indoors than had been reported outdoors. The effect was believed
to be due to faulty stoves or chimneys. This finding led the authors
to say that "If 1 out of 100 houses has a falling chimney or a failing
stove during smogs, one begins to wonder how far Indoor concentrations
of air pollutants play a role 1n causing premature death 1n persons
with failing circulation and respiration and what role CO plays in the
process" [69].
In a laboratory room at the Department of Chemical Engineering
and Chemical Technology, Imperial College, London, England, Wilson [674]
measured the decay rates of sulfur dioxide concentrations which followed
the closing of windows which had been open to the polluted London atmo-
sphere. Simultaneous concentration measurements of the decay of known
amounts of nonreactive helium and of 50^ (introduced at the start of
the experiment) permitted estimates of the extent to which S02 was
absorbed onto surfaces or otherwise removed by indoor sinks. "The rate
of air change in the room was measured by liberating some helium at the
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start of an experiment and determining the concentration at intervals
with a chromatograph." The helium was not adsorbed and the reduction
of its concentration was a measure of gas leakage rates out of the
closed room which would affect S02 and helium alike.
Wilson found that S02 had a half-life of 40 to 60 minutes
and that the equilibrium concentrations of SOg in the test room were
controlled mainly by processes at the surface rather than by transport
processes. Wilson's work is noteworthy, in addition, for his experi-
ments with a controlled concentration of S02 liberated within the test
room at a constant rate. Air containing a 2 mg/m^ concentration of SOg
was placed in contact with absorbing surfaces in a closed vessel over
measured periods of time, after which SOg concentrations were again
measured. The resulting reductions of S02 concentration were a measure
of absorption. Table 13 illustrates this. The authors said "that the
walls, floor and treated wood surfaces had little effect in removing
sulfur dioxide; and that only the ceiling was reasonably effective" [694]
TABLE 13. CONCENTRATIONS OF SO2 ABSORBED BY VARIOUS MATERIALS [694]
Material
Varnished Wood
Painted Wall
Floor
Ceiling
Softwood
Corduroy
Knitted Wool
2
Sulfur Dioxide Absorbed (mg/m )
After 1/2 Hour
0.11
0.13
0.36
0.53
1.70
0.65
1.85
After 1 Hour
0.11
0.13
0.36
0.99
2.82
1.20
3.46
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Wilson concluded that an increase in transport to surfaces
which have reached a state of equilibrium in S02 adsorption capacity
cannot reduce the airborne S02 concentrations further. This finding,
that materials reach a capacity for S02 adsorption, was also observed
by Biersteker et al. [69] and Grafe [243]. In these investigations,
increased outdoor 502 concentrations and subsequent increased inflow of
S02 were observed to be ineffective in changing the indoor adsorption
patterns.
A series of papers [589, 591, 590, 588, 592, 587, 250] on
adsorption by indoor surfaces shows, that of the surfaces studied,
leather is the most efficient surface for sulfur dioxide adsorption
followed by natural fibers (wool, cotton). In general organic materials
such as leather and natural fibers are more efficient adsorbers of SCL
than inorganic materials or manufactured organic materials such as
artificial fibers. Spedding [589] concludes that adsorption of S02 by
many surfaces is dependent upon the moisture content of the surfaces and
thus of the atmosphere. Previous studies have reached the same general
conclusions [587, 681, 315].
Cox and Penkett [144] found that the first order decay of S02
indicates an irreversible adsorption on the surface of the material.
As humidity is raised from 30 to 86 percent, the speed at which S02
1s deposited upon gloss paint is increased by a factor of 32.7 [144].
The authors hypothesize that the S02 is probably taken up by a film of
water associated with the surface; after adsorption it will be converted
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to sulfate at a rate dependent upon the extent to which materials from
the surface are dissolved 1n the water film. They concluded that
"Sulfur dioxide 1s going to disappear very rapidly onto the walls of
any containing system at high relative humidities" [144].
Benson et al. [65] conclude that sulfur dioxide 1s removed
from Interior air by adsorption at a rate dependent primarily on the
properties of the Interior surfaces and only slightly on the rate of
transport to the surfaces. The authors reported Wilson's [694] findings
that "stirring" the air was effective 1n reducing S02 concentrations by
10 to 40 percent; the higher the Initial concentration 1n the room the
greater was the percentage reduction. The reviewers do not discuss the
role higher relative humidity plays In Increasing S02 adsorption on all
Interior surfaces.
There have not been studies which directly addressed the
behavior of sulfurlc add and other sulfates in the Indoor environment.
It has been determined from previous Investigations of atmospheric
chemistry processes that S02 does not remain unaltered 1n the atmo-
sphere, but is oxidized to sulfuric acid and other sulfates by several
environmental-dependent mechanisms (most of which are not well understood)
Involving reactive agents such as photochemical smog, ammonia, catalytic
metals, and fine partlculates [664]. The rate of formation and, to some
extent, the final sulfate form, are determined by the different mechan-
ism paths. The most Important sulfate mechanisms Identified to date are
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categorized in Table 14 on the following page, reproduced from work by
Wilson and his associates [695]. Those sulfate compounds currently known
to be formed 1n the atmosphere from gas-particle conversions involving
S02 oxidation are listed in Table 15 from Wilson [695], which in addition
shows those sulfates emitted directly by industrial or by natural sources.
Studies of the S02 * sulfate transformations are proceeding
vigorously in the larger context of ambient air pollution research.
For example, the Electric Power Research Institute Inc. (EPRI) is
sponsoring the on-going Sulfate Regional Experiment (SURE). Currently,
efforts in this research are directed towards an experimental design
for a major regional air chemistry study of how particulate sulfate
concentrations may relate to sulfur oxide emissions based upon an
evaluation of existing air quality data, chemical processes, and numer-
ical modeling capabilities.
Of the transformation mechanisms known, few, if any, give
promise of providing an explanation for the conversion of S02 to
sulfate in an airborne phase in an indoor residential environment.
A principal reason for this is the relatively long reaction time for
S02 -> SO, reactions (typically greater than the air exchange rates of
residences) and the short times of S02 in the indoor environment (typi-
cally less than an hour).
4.2 CARBON MONOXIDE
Benson et al. [65] concluded that carbon monoxide indoor-
outdoor concentration relationships are similar to those of sulfur
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TABLE 14. MECHANISMS BY WHICH SULFUR DIOXIDE IS CONVERTED TO SUIPATES [695]
t
_j
o
ro
i
Mechanism
1. Direct photo-
oxidation.
2. Indirect photo-
oxidation.
3. Air oxidation in
liquid droplets.
4. Catalyzed oxidation
in liquid droplets.
5. Catalyzed oxidation
on dry surfaces.
Overall reaction
SO,
light, oxygen
water
smog, water, NOX;
ganic, oxidants,
hydroxyl radical (OH)
water
SO oxygen, liquid water
heavy metal ions
SO oxygen, water ^
. carbon, particulate
Factors on which
sulfate formation
primarily depends
Sulfur dioxide concen-
tration, sunlight
intensity.
Sulfur dioxide concen-
tration, organic oxidant
concentration, OH, NO .
Ammonia concentration.
Concentration of heavy
metal (Fe, V, Hn) ions.
Carbon-particle concen-
tration (surface area),
-------
TABI£ 15. KNOWN ATMOSPHERIC SUIFATES [695]
Formula Names
Sulfuric acid (oil of
H2)304 vitrol)
NH.HSO, - Acid ammonium sulfate
(NH,)_H(SO,)2 \Triammonium acid disul-
fate (Letovicite)
Ammonium sulfate
(NH4)2S04 (Mascagnite)
Sodium sulfate
Na2SO, (Glauber's salt)
Calcium sulfate
CaSO, (gypsum)
Magnesium sulfate
MgSO, (Epsom salts)
Sources
Atmospheric oxidation
of S0_; direct from
manufacturing ,
Oxidation of SCL with
NH3 addition.
Oxidation of 'SO,, plus
NH3,
Oxidation of SO. plus
NH3. ^
Paper pulping by
kraft process.
(1) Wind-blown dust.
(2) Manufacture of
gypsum products.
(1) Sea spray.
(2) Paper pulping.
Notable chemical
properties
Strong acid, very
hygroscopic (drying
agent at low RH) .
Strong acid,
hygroscopic.
Acidic, deliquenscent
(?) at ^65% RH.
Weak acid, water-
soluble, deliques-
cent at 80% RH.
Water-soluble,
deliquescent at 84% .
RH; relatively inert.
Low solubility in
ILOj relatively
inert
Very hygroscopic;
relatively inert
and non-toxic,
Probable Size
class by mass
particle
Diameter, Dp
0.1 - 1.0 ym
0.1 - 1.0 ym
0.1 - 1.0 ym
0.1 - 1.0 ym
Dp > 0.5 ym
(uncontrolled
pulp mill)
D > lym
Dp > 1 ym
(sea spray)
Dp > 0,5 ym
-------
dioxide in that (a) concentrations are generally higher outdoors than
indoors and (b) increases in concentrations outdoors do not lead to
proportional increases inside. Further, they point out that short-
term peaks in outdoor CO concentrations, like those of SOp, are not
reflected by indoor concentration patterns. There are important dif-
ferences, however, in the reactivity of the two gases and in their
residence times within buildings. Carbon monoxide is relatively unre-
active and decays very slowly compared to S02. Further, CO is of
particular interest because it is not only an outdoor-generated pol-
lutant but is an indoor-generated product, arising from gas-fired
appliances, leaky furnaces and chimneys, and attached garages. The
significance of indoor-generated CO is substantially greater than that
of Indoor-generated SOg.
In a comprehensive study conducted by the General Electric
Company [233] the behavior of carbon monoxide was investigated in two
high rise buildings, one of them an air-rights structure. As reported
in the section on pollutant sources, indoor CO concentrations were
normally lower than outdoor concentrations at all heights above the
roadway when outdoor concentrations are high. Conversely, indoor con-
centrations were higher than outdoor concentrations when outdoor con-
centrations were low. At heights greater than 100 feet above the
roadway, concentrations of CO were larger indoors than outdoors; this
was attributed to the entrapment of CO within the building (i.e., inside
the building it was not removed by the air transport processes which
were operating actively at this level to dissipate CO in the air outside
the building) [233].
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In the comprehensive study of buildings in Hartford, Connec-
ticut by Yocom [713], carbon monoxide was monitored at four locations;
far outdoors, near outdoors, near indoors and far indoors. Far indoor/
far outdoor concentration ratios were found to approximate 1.0 for all
structures when a long averaging time was used as a basis for compar-
ison. For comparisons of short-term CO concentrations, however, con-
centrations indoors were found to lag behind those found outdoors.
Outdoor CO concentrations showed gradual peaks corresponding to the
hours from 6 to 9 A.M. during which outdoor CO concentrations steadily
rose above those found Indoors. However, as the CO concentrations were
subsequently depleted outdoors, Indoor concentrations rose above those
found outdoors but to levels less than those found earlier outdoors.
The authors also determined an exponential decay constant for carbon
monoxide by both closing off the ventilation and "spiking" the indoor
atmosphere with CO.
The authors described the response Indoors to peak outdoor
concentrations at one of the homes monitored with the windows and doors
closed and the air conditioner turned off as sluggish, but highly
dependent upon the air exchange rate of the building monitored. Further,
the authors found that the heating system had little effect on CO levels
except 1n a home 1n which a coal-fired hot air heating system was
believed to be faulty. Here the CO and SOg levels were found in concen-
trations high enough to be of concern for possible adverse health
effects. Finally, the authors found that the carbon monoxide emissions
from a gas stove had a significant effect on indoor CO levels [713].
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In a study conducted in California on the relation between
indoor and outdoor concentrations of nitrogen oxides, carbon monoxide
was also monitored both inside and outside a building [158]. The
investigators reported results similar to those found by Yocom et al.
[713] in which the CO concentrations indoors lagged behind the peak
concentrations outdoors; these latter corresponding to peak automobile
traffic nearby. The authors concluded, after finding that nitrogen
oxide showed similar temporal behavior, that both NO and CO levels
/\
could be reduced by restricting the intake of outside air during these
periods.
Studies of the concentrations and behavior of carbon monoxide
emitted from gas-fired appliances in the indoor environment have shown
that this source can contribute concentrations of significant amounts
[143]. The Institute of Gas Technology in conjunction with Battelle
Columbus conducted a survey of 57 homes equipped with gas cooking
kitchens in order to determine the concentrations of CO and NO levels
- - - A
in the kitchen. The investigators monitored air 6-10 feet from the
cooking unit at a height of about 3-1/2 feet from the floor. Samples
of air were collected over a period of one hour from the start of
cooking the main meal. The authors concluded that the concentrations
of CO were negligibly small compared with the 1-hour standard of 35 ppm.
In 71 percent of these homes, the concentrations were less than the 8-hour
standard of 9 ppm. One of the homes, however, had a CO concentration
for one hour above the 35 ppm level (39.4 ppm) as a result of a badly
adjusted oven. A repeat sample after adjusting the oven measured
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7.1 ppm during cooking of the same meal [184]. The finding concerning a
badly adjusted oven represented 1.75 percent of the homes surveyed. While
not statistically significant in Itself, the finding would be of concern
if this percentage of maladjustment were an adequate representation of
all homes equipped with gas-fired appliances, particularly considering
the fact that the 39.4 ppm CO concentration was monitored as far away
as 6 to 10 feet from the cooking unit.
In a more recent study conducted in Hartford, Connecticut,
CO concentrations were monitored in the kitchen and three other locations
In four private residences for two-week periods in the spring and early
summer of 1973 and again in the following fall and winter [143]. The
Investigators found that the CO concentrations were higher inside than
outside, with one exception, and always higher in the kitchen than in other
parts of the house. Further, the authors found 40 percent of the indoor
concentrations above the 8-hour NAAQS for CO at all three indoor loca-
tions 1n House No. 4 where CO concentrations were highest among the
four houses surveyed. Table 16 shows results of this survey.
It can be seen from this table that the CO concentrations
were differentially dependent upon background or outside concentrations
and indoor stove use. In addition, the patterns of indoor CO are influ-
enced by interior design features and ventilation characteristics.
Further, the half-life of CO was found to be 2.1 hours in House No. 2
during an unoccupied period [143].
Most recently the Lawrence Berkeley Laboratories conducted
pilot measurements of combustion-generated indoor air pollution for the
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TABIE 16. SUMMARY OF INDOOR/OUTDOOR CO DATA IN EACH HOME FOR BOTH SEASONS
House
Number
1
2
3
4
Sampling
Period
Spring -
Summer
Fall-
Winter
1st Half
Fall-
Wintei
2nd Half
Spring -
Summer
Spring -
Summer
Fall-
Winter
1st Half
Fall-
Winter
2nd Half
Fall-
Wlnter
Daily Average CO Concentration
of Each Location /ig/m*
Kitchen
Over
Stove
-
4190
4790
3000
4310
7820
7130
9070
Kitchen
1 m
from Stove
4490
3520
4210
-
-
6420
6620
9000
Living
Room
4070
3230
-
3080
3210
5070
.
8190
Bed
Room
4170
^_
3830
2900
2680
^,
5500
Outside
3480
1670
2310
2940
2230
3380
2500
2410
Total
Stove
(Oven Plus
Burners)
Use
Min./Day
198
106
(Unavail-
able)
43
37
66
115
201
Number
of Days
of Valid
Data
9
4
6
3
13
6
8
6
Adapted from Cote et al. [H3].
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U.S. Energy Research and Development Administration at six homes in
Berkeley and Albany, California; all fitted with gas heating systems
and five with gas-fired stoves. Results of the CO measurements shown
in Tables 8 and 9 in Section 3.0, again are observed to exceed the
1-hour NAAQS for CO [308].
Radford [504] reported that of 302 old houses surveyed in East
Baltimore 20 percent had elevated levels of 10 ppm or more of CO, 4 percent
showed levels at 20 ppm or more and 1 percent exceeded 50 ppm. In the houses
where the higher CO concentrations were found, the problem was traced
to unvented space heaters or stoves used for heating, to oil or gas
fired furnaces used for central heating and to combinations of these
sources. These data may be compared with an analysis conducted by
Morrison [436] of deaths in 1967 due to accidentally induced CO poisonings.
Although 68 percent of the death certificates revealed automobiles as the
leading cause of CO poisonings, heating equipment accounted for 26 per-
cent (over 300) of these deaths. Of these related to heating equipment,
11 percent were due to furnaces, 19 percent specifically identified as
space heaters and 64 percent were caused by other sources including stoves,
refrigerators and charcoal.
Carbon monoxide, as a product of the combustion of tobacco,
has been studied as a pollutant to which the smoker and nonsmoker are
exposed. The smoker is exposed through direct inhalation of the smoke
(mainstream) while the nonsmoker involuntarily inhales the tobacco
smoke from the environment (sidestream). The exposures to carbon monoxide
by the "involuntary smoker" from mainstream and sidestream smoke have been
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the subject of increasing study in recent years. Although carbon monox-
ide is often used as an indicator of other pollutants resulting from
tobacco, because it is both easy to measure and predict, it has been
studied in its own right as being a possible health risk to nonsmokers
[656]. Bridge and Corn have noted that "the CO generated by one cigar
is approximately 1.7 to 2.5 times as much as that generated from simul-
taneously smoking three cigarettes" [88],
Carboxyhemoglobin (COHb) level measurements for groups of
passive smokers have been conducted by various investigators in attempts
to assess the exposure and health risk of CO from smoking [39, 40, 41,
270, 531, 610].
In a study conducted to assess the nonsmokers' exposure to smoke,
Bridge and Corn [88] monitored carbon monoxide in two rooms before
and after two 90-minute parties where roughly half of the participants
o
were smokers. In the two rooms (5120 and 3570 ft ) background concen-
trations of CO were 1 and 2 ppm CO respectively. During the parties
the average CO concentrations were 7 and 9 ppm respectively attributed
to 50 cigarettes and 17 cigars at the first party and 63 cigarettes and
10 cigars at the second party. Bridge and Corn found that "if the CO
emitted by room occupants is taken into account, the measured concen-
trations are reduced to about 6.5 and 8 ppm for the first and second
parties, respectively" [88]. Results of their work are shown in
Table 17.
Bridge and Corn concluded that "concentrations of CO from
cigarette and cigar smoking do not present an inhalation hazard to
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nonsmokers. However, suspended particulate matter generated from
cigarette and cigar smoking was calculated to reach concentrations
considered to be excessive using the criterion of ambient air quality
standards for suspended particulate matter suggested by Federal criteria
(75 ng/m3)" [88].
TABLE 17. MEASURED CONCENTRATIONS OF CARBON MONOXIDE IN THE EXPOSURE CHAMBER
FROM TOTAL CIGAR SMOKE FOR ONE CIGAR SMOKED AT EACH OF 1, 3, 6, and 8
VOLUMETRIC AIR CHANGES/HOUR gg
Exposure
Chamber Exhaust
Rate
(cfm)
5.4
5.4 (repeat)
43.4
43.4 (repeat)
Air
Changes
Per Hour
1
1
8
8
. No. of
Cigars
Smoked
1
1
1
1
Smoking
Time
(Minutes)
28
28
30
28
Butt
Length
(mm)
31
30
28
35
CO Cone (ppm)*
Peak
57
58
24
25
Initial
5
1
2
1
* Ambient Air Quality Standard for 1 Hour is 35 ppm and for 8 Hours is 9 ppm.
In a study to assess the health aspects of smoking 1n trans-
port aircraft carbon monoxide concentrations were monitored at four
locations in 18 Military Aircraft Command jet aircraft for*6 to 7
hour flights and in eight civil domestic flights of 45 minute to 1
hour durations. For the MAC flights the highest CO concentration was
5 ppm CO in one location in one flight. In the total of 72 MAC flight
samples, 32 were 2 ppm or less, 25 were 3 ppm, 14 were 4 ppm and 1 was
5 ppm. For the domestic flights, no CO concentrations greater than
2 ppm were observed out of 24 samples taken. This discrepancy in MAC
and civil aircraft flights is attributed to the more rapid exchange of
-111-
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air in civil aircraft and the almost CO-free air entering the aircraft
at cruising altitude [662].
In a study conducted by Penkala and de Oliveira [486] a
literature review was conducted to offer a comparison to the authors'
subsequent measures of CO and Suspended Particulate Matter (SPM) in an
exposure chamber. The authors' results are presented with those of
other authors in Table 18. The results of the authors' measurements
of CO in a room occupied by a smoker and a nonsmoker are shown in
Table 19.
In comparing the removal rates of CO and SPM in the exposure
chamber the authors found the concentration half-lives to be 83.5 and
4.8 minutes respectively. Penkala and de Oliveira concluded that CO
should not be used as a tracer for tobacco smoke without correcting
for this difference [486].
Public gatherings for sporting events, concerts and other
activities are also sources for the accumulation of concentrations of
tobacco smoke. Elliot and Rowe [185] measured Total Suspended Partic-
ulate (TSP), CO and benzo(a)pyrene before and after events at three
arenas. In one event attended by 2,000 persons the arena was not air
conditioned and had no signs restricting smoking. The background
carbon monoxide was 3.0 ppm which rose to 25 ppm during the event.
Another place of public assembly in which CO may be found in
high concentrations is an ice skating rink. Rinks are peculiar sources
of CO not only from tobacco smoke but also from the large propane-
fueled ice resurfacing machines. In one rink in Seattle monitoring
-112-
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TABLE 18. MEASURES OF CO AND SPM IN AN EXPOSURE CHAMBER [ 485 ]
Investigator
Rosanno and Owens (1976)
Bridge and Com (1972)
Bogardus and Ramskill (1968)
Westanabe and Robasld (1967)
Harke (1972)
Penkala and Oe Oliveira (1975)
Milligrams
Mainstream
Smoke
23
23
--
22.0-28.8
..
CO per Cigarette
Sidestream
Smoke
63
~
--
«
Total
86
124
55
82-155
77
82.7
Ratio
Sidestream
Mainstream
CO
2.75
9.4
2.75-4.4
--
~
TABLE 19. ESTIMATE OF CO CONCENTRATIONS IN A 9.2 m3 ROOM
OCCUPIED BY A SMOKER AND A NON-SMOKER [485]
Ventilation Rate
. (air changes/hour)
0
1
2. 1 \ good
> ventilation
7.5 ) practice
CO Concentrations (mg/m3)
Minimum
15.2
3.3
1.1
0.0
Maximum
22.5
10.6
8.4
7.3
Mean
18.6
6.2
3.6
1.2
-113-
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took place after 15 children became ill and suffered a variety of
symptoms including headaches, nausea and vomiting. Carbon monoxide
concentrations averaged for one hour were found to be as high as 304
ppm. Table 20 shows the average CO concentrations at this rink and
Table 21 shows the results of a survey of other rinks conducted to
determine if they too were a significant source of CO exposure,[336].
In the ice skating arena a gas-powered resurfacing machine
was used. CO levels rose to a level of 175 ppm in 17 minutes, and remained
at 170 ppm 15 minutes after the machine was stopped. The authors estimate
that there are approximately 600-700 ice skating arenas in the United States,
most of which use ice resurfacing machines that produce significant amounts
of CO. Although catalytic mufflers and better ventilation practices are
offered as solutions, the authors suggest electrically powered ice resurfac-
ing machines are probably best [336].
Although "indoor" is usually taken to mean the interior of a
building, It can also define the passenger compartments of vehicles. Of
significant concern to the public is the exposure to CO concentrations
while riding in or operating motor vehicles since automobiles are by far
the largest anthropogenic source of carbon monoxide. In urban areas such
as Boston, Washington, D.C. and Los Angeles more than 98 percent of the
CO emissions are produced by automobiles. While many researchers have
studied emissions of CO from automobiles and exposures to ambient con-
centrations of CO in urban areas, there have been few studies of the
-114-
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TABLE 20. CONCENTRATIONS OF CO RECORDED IN ICE-SKATING ARENA DURING
OPERATION OF PROPANE-POWERED ICE-RESURFACING MACHINE
GENERATED FOR 10 MINUTES EVERY 1 OR 2 HOURS [336]
Clock (Hours)
4-5
5-6
6-7
7-8
8-9
9-10
10-11
11-12
EPA 1-hour standard
CO Level (1 Hour Average) ppm
214
304
224
225
186
157
261
219
35
TABLE 21. RESULTS OF INITIAL SURVEY OF CARBON MONOXIDE LEVELS IN ICE SKATING
ARENA EN KING COUNTY, WASHINGTON [336]
Ice Skating
Arena
Highland
Ballard
Bellevue
Burl en
Crossroads
Coliseum
CO Level
(Maximum)
(ppm)
250
45
75
100
175
12
Number of
Inspections
4
1
1
1
1
1
s
Remarks
Arena now opens doors to
augment ventilation
Doors opened prior to test
(not normally done)
Machine run only 7 minutes
(normally machine runs
10-15 minutes)
No public skating
-115-
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CO exposures to commuters in the enclosed environments of automobiles,
mass transit and buses.
Cortese and Spang!er [142] conducted a study of CO exposures
to commuters utilizing private automobiles and mass transit by equipping
62 volunteers with personal monitoring instruments for measurement of
the CO concentrations to which they were exposed. The results of the
aggregate personal exposure data revealed that for all commuting con-
centrations, 10 percent of the values are greater than 21 ppm, 5 percent
are greater than 26 ppm and 1 percent are greater than 36 ppm. In
analyzing concentrations reported at fixed locations the authors con-
cluded that these ambient CO concentrations measured at these fixed
sites significantly under-represent the 1-hour exposures actually
experienced by commuters. The investigators demonstrated that the
method of travel and exposure to cigarette smoke were the two factors
significantly influencing personal exposures to CO during commuting.
Travel on rail mass transit resulted in a CO exposure of less than half
that of auto travel.
Peterson and Sabersky [489] performed a series of experi-
ments to determine the concentrations of certain pollutants inside a car
under typical driving conditions. The experiments were conducted
during the summer months in the Los Angeles area and measurements were
taken of CO, 0,, NO and NOV. All of the experiments were conducted
<5 A
with the vehicle windows closed and with the air conditioner on during
most of the vehicle run. Samples were taken within the vehicle interior
and from outside air drawn into an analyzer through a duct passing out
-116-
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through a slit in the door window. The authors concluded that inside CO
concentrations on the average were the same as those in the surrounding
atmosphere outside and were below the National Ambient Air Quality
Standard levels for CO. Although the magnitude of the concentrations
were 15 to 25 ppm, the concentrations were sometimes higher for short
periods of time. In one severe traffic congestion the concentration
reached 45 ppm for 3 minutes.
It is noteworthy, however, that the ambient air concentrations
monitored at fixed locations near the route showed a peak reading of
8 ppm CO. The number of values exceeding the 8-hour NAAQS for CO in
Burbank was 1,101 of a possible 4,406 valid values in 1973. Further,
since attempts were made to monitor under a range of typical driving con-
ditions in Los Angeles, the time period on the freeway sections which were
s
often congested was minimal; much of the monitoring was conducted during
off-peak conditions. Presumably, the CO exposures to commuters in Los
Angeles during peak traffic conditions are often significantly above NAAQS
levels, particularly on days when the one-hour and eight-hour standards
are exceeded at fixed locations.
Brice and Roester [84] monitored concentrations of CO in moving
vehicles in six cities. The data collected showed a maximum concentration
of CO inside moving vehicles, in traffic, of 77 ppm (St. Louis). In
another report exposures to levels of CO on school buses were found to
be higher than the recommended one-hour standard of 35 ppm [356]. This
latter study was performed after several children became ill, two
requiring hospitalization.
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4.3 CARBON DIOXIDE
Like carbon monoxide, carbon dioxide is a relatively stable
pollutant and would be expected to have a relatively long residence
time in indoor air. Unlike carbon monoxide, however, carbon dioxide
concentrations indoors would likely be a function of the number of
occupants. Additionally carbon dioxide is a product of complete com-
bustion and is therefore emitted by gas stoves and appliances and
building heating plants. Only one reference was found concerning the
indoor concentrations of carbon dioxide. Ishido [326] found indoor
levels of C02 ranging from 0.03 to 0.32 percent (300 to 3,200 ppm).
This is from 1 to 10 times the normal ambient air level of C0« [557].
Bush and Segal! reported that C02 is not removed from the indoor
environment by air conditioning [100],
4.4 NITROGEN OXIDES AND NITRATES
Concentrations of nitrogen oxides found indoors are attributed
to both infiltration from the outdoor environment and to generation from
household heating and cooking appliances, primarily gas-fired. In field
measurements in a home in Hartford, Connecticut, Cote et al. [143] found
that the half-life of NO was 1.8 hours while N02 decayed with a half-
life of 0.6 hours. Further the investigators found that the ratios of
HO2 to NO varied somewhat but that there was generally more NO than N02
generated from the gas stove. Hollowell et al. [308] reported concen-
trations of NO which were more than twice those of NOp in a home with a
-118-
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gas-fired stove with no duct and an exhaust fan off. Table 22 shows the
results of their findings.
TABIE 22. CONCENTRATIONS OF NO AND NOg (jig/3) OBSERVED IN HOMES
WITH GAS OVENS* [308]
Home ID #
Ventilation Conditions
NO (Mg/m3)
N02(/ig/m )
2
No Duct
Fan Off
2000
850
No Duct
Fan On
1000
320
3
Duct
'No Fan
500
150
4
Duct
No Fan
150
95
Measurements in center of kitchen, approximately 1.5 meters above the floor, with the gas
oven at 550°F for approximately 20 minutes.
The investigators found "elevated indoor particulate nitrogen
levels" (this is Hollowell's terminology) in the home equipped with a
gas furnace [308]. These results compare favorably with those reported
by Eaton et al. [178] where a maximum NO value of 1.0 ppm (2000 yg/m3)
/\
was observed in a kitchen after a 6-minute cooking time with a gas
burner. In controlled tests for indoor oxides of nitrogen the investi-
gators also reported higher concentrations of NO than NOg. Derham
et al. [158] reported on the concentrations of nitrogen oxides inside
and outside a building in Pasadena, California, a city where embient
concentrations of these pollutants are known to be high. NO was found
to behave very similarly to monitored CO with peaks associated with
rush hour automobile traffic outdoors; since their behavior was similar
-119-
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no significant chemical reactions were believed to be involved in
establishing the indoor concentrations of NO. Indoor 03 concentra-
tions during the experiments were relatively low when NO was present.
High NO and N02 concentrations were found in the months from about
October to March whereas high 03 concentrations were found in the months
from March to October. Finally, the results support findings that NO
and 03 do not co-exist indoors except in small quantities [158].
No investigations have been made to determine possible indoor
mechanisms for nitrate or nitrosamine formation although Hollowell et al.
[308] made some preliminary tests in a home equipped with a gas furnace.
Experiments to measure those nitrogen species in kitchens equipped with
gas-fired appliances would help to establish these mechanisms if such.
conversions take place.
Indoor NO and N02 concentrations, to the extent that these
arise from outdoor-generated pollution, are dependent upon the location
of the building in relation to the point and area sources at which NO
and N02 emissions are generated. Atuomobiles are the major source of
NO and NOg emissions. The location of the building in relation to auto-
mobile traffic patterns will, therefore, have an important influence on
the levels of outdoor concentrations of NOX which are available to enter
the building.
Presumably, the N0/N02 ratio would be higher in buildings
close to roads than those further away. In the latter case the N0/N02
ratio will not only be lower but might as a result be subject to relatively
-120-
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higher concentrations of 03 (which is not generated directly by automobile
traffic but indirectly through photochemical reactions involving auto-
motive emissions which have typically moved many miles from the emission
sources by the time oxidant generation occurs). A further discussion of
reasons for the relatively low 03 concentrations near heavily travelled
highways appears later, in Section 4.5. These conditions, as taking
place outdoors and monitored at continuous monitoring stations in urban
and suburban locations, have been discussed by Altschuller and Bufalini
in 1971 [8].
Observed concentrations of NO are highly dependent upon the
meteorological conditions: indoor concentration measurements taken on
a day on which there was no inversion layer indicated low NO levels at
all times [158]. Figure 4 from the Derham et al. study, shows the
correlation between external and internal NO levels.
0.5-
0.4
10.3
00.2
0.1
/
:-^.
12
noon
3
prn
Tim*
/ j v1^ M>-
/ / V
/ liV Ventilation turned off
--^-r* t ,.
c Q 10
°' ' | 6 ' ' 9
am ventiiation tinned on
Figure 4. Relative NO levels as recorded outdoors (1), indoors (2), an
reported by the Pasadena APCD station (3) on a typical day [l58J.
midnight arn
and as
-121-
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4.5 PHOTOCHEMICAL OXIDANTS
Ozone and PAN (peroxyacetyl nitrate) are secondary pollutants
in the ambient atmosphere, typically arising from interactions of
automobile-generated hydrocarbons and NOX emissions in the presence of
sunlight. Ozone may also be generated independently in indoor and out-
door environments through electrical discharge at equipment such as air
cleaning predpltators and fluorescent lights.
Ozone and PAN are also highly reactive species and, like S02»
do not persist in high concentrations indoors even when outdoor con-
centrations are high, because of rapid decay through adsorption on indoor
surfaces. 03 and PAN concentrations indoors are highly dependent on the
location of the building monitored in relation to large urban areas.
Ambient concentrations of Og and PAN are a function of particular meteoro-
logical conditions of low wind, low atmospheric stability and large
amounts of sunlight as well as the presence of sources of hydrocarbons
and NO . The topography of the urban area, its size, and its location
A
govern the climatological history of episodic pollution potential [309].
The daily generation of NO, N0« and hydrocarbons, particularly from
automobile emissions, during these episodic conditions determine the
concentrations of 0, and PAN within the large urban plume. The location
of the building monitored, 1n relation to wind direction and the urban
plume, largely determines the concentrations of outside 03 and PAN which
can infiltrate into the indoor environment. The immediate vicinity of
a building near a heavily traveled highway (including buildings within
-122-
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the urban core) may have concentrations of 0- which are relatively low.
This observation has been attributed to the ability which high concentra-
tions of NO, emitted from automobiles, have to scavenge the (L. Investi-
gations of 03 and NO indoors have verified this relationship [561].
Ambient Og concentrations are high in the warmer months and occur during
daylight hours. Figures 5, 6, and 7 show the indoor-outdoor concentrations
of 03 on three summer days in California [534, 439].
Ozone does not usually originate in significant quantities in
indoor environments, its levels being closely related to the outdoor
ozone levels. Indoor-generated ozone, from electrical equipment opera-
tions, is not believed to be an important source in the nonworkplace
indoor environment. Many of the studies concerned with the behavior
and fate of ozone indoors have involved numerical models which relate
s
indoor ozone concentrations to those outdoors. An example of this is
the Hales et al. [262] linear combination model, which when used for
verification purposes, was found to be in agreement with actual ozone
concentrations in hallways of the selected test area. The concentrations
were found to vary from room to room depending on parameters such as
local ventilation and room geometry. The Hales et al. [262] study served
to verify the theoretical ventilation model of Shair and Heitner [561],
Development of this model was based, in part, on results of earlier
tracer experiments to obtain quantitative data regarding actual residence
time distributions of the tracer (SFg) in rooms and hallways [171]. A
simple "stirred tank" ventilation model was used to interpret experiments
involving the decay of ozone in the presence of various common materials
-123-
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O.3
0.2
OJ
* OUTDOOR CONCENTRATION OF
Oj REPORTED BT THE UXAPCD
fttSADENA STATION
-*- MDOOR CONCENTRATION OF
Oj IN THOMAS BUUXNG
AUGUST 8.1971
45678910 II 12 I 234567 8 9 10 II 12
MORNING NOON EVENING
Figure 5. Ozone concentration vs. time of day for Thomas Building, August 8, 1971.
03
OUTDOOR CONCENTRATION OF
Oj REPORTED BT THE LAAPCO
PASADENA STATO*
-»- MOOOR CONCENTRATION OF
Oj IN SW.DING LABORATORY
(2 I 23456789 10 II 12 I Z3456769IOIII2
MORNING NOON EVENING
Figure 6. Ozone concentration vs. time of day for Spalding Laboratory, June 27, 1971.
0.20
O.I5
O °-
;0. 0.10
0.05
0.
" J
: ji
4||
I«J
y,i
,'i i
w
/
/ . .
JJ -
It ll
J!"
x' Win
r }V\
i '
\
^- INDOOR
CONCENTRATION
OF 0,IN
ALTADENA HOME
JULY 25, 1971
/^
» \
^
\
\
, , . ^,..4,,.,*
9 10 II IZ I 2 34 56 7 8 910 II
MORNING EVENING
Figure 7. Ozone concentration vs. time of day in private home in Altadena, July 25, 1971.
Note: All figures are from Sabersky et al.
-124-
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in a lucite chamber [534]. All these modeling attempts utilize the
fact that ozone typically undergoes a first order heterogeneous decom-
position mechanism. Studies conducted in rooms of various sizes, indi-
cated the ozone decay rate is directly related to the surface-to-volume
ratio [439]. Table 23, from the same study, shows the measured values
of ozone decomposition rates for several common surfaces, as determined
in the lucite chamber. It can be seen that the higher rate constants
are characteristic of materials such as rubber, fabrics and plastics;
metal and glass have lower rate constants. Hales et al. [262] observed
that rooms with rugs, excess furniture, excess books and papers had
lower ozone levels than did those with concrete floors or those rooms
which appear to be neater, with few books and papers present.
In research by Mueller et al. [439], ozone decomposition studies
were performed in a closed bedroom. The results showed a short, six
minute half-life of ozone in the bedroom which suggests rapid decomposition
of this pollutant after it penetrates a typical living space. Research
by Ellis and Tometz [187] tested the "ozone decomposing catalytic
efficiency" (the author's terminology) of various materials at room tem-
perature in a laboratory. The results of their efforts are shown in
Table 24; the best catalysts are coconut charcoal and activated carbon.
Most researchers who have studied ozone behavior indoors have concluded
that additional studies should be conducted to further understand the
detailed mechanisms of ozone decay on common surfaces.
-125-
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TABLE 23. MEASURED VALUES OF OZONE DECOMPOSITION RATES
FOR SEVERAL COMMON SURFACES [534]
Material
Cotton muslin
Lamb's wool
Neoprene
Plywood (1 side varnished)
Nylon
Polyethylene sheet
Linen
Lucite
Aluminum
Plate glass
K. ft3/£t2
0.214
0. 208
0.19
0. 06
0.063
0.048
0.0185
0.012
0.002
0.002
- min
-* 0. 029
-* 0.008
-* 0.03
-* o.oi
-* 0.001
-* 0. 020
-*- 0. 0107
* 0.001
-*- o.ooi
*- o. ooi
TABLE 24. RESULTS OF TESTS OF OZONE-DECOMPOSITION CATALYTIC
EFFICIENCY OF VARIOUS MATERIALS [ 187 ]
% Ozone Removed
Materials
90-100
70 - 80
50-60
40-50
30-40
10 - 20
0-10
coconut charcoal, activated carbon
NiO, NiO-CuO mixture, NiO-FejO4 mixture, Hopcalite
MnO2, Ag, Fe3O4, SnO, Pb3O4, Ag2O, NiO-SnO mixture
mixture, CuO-Fe3O4 mixture, CoO, Fe2O3, CuO,
Sb205, PbO
ZnO, A12O3, Ci^Oj, CuO-SnO mixture
MgO, 500 W lamp, Ni
CrOj, CdO, Bi2O3, glass wool, zeolite catalyst,
silica-alumina catalyst, Ft
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4.6 HYDROCARBONS (NON PHOTOCHEMICAL ORGANICS)
A study by Bridbord and others in 1975 [86] examined the
behavior of halogenated hydrocarbons in indoor environments. The authors
described a theoretical basis for calculating the rate of decay of indoor
pollutant concentrations (assuming a chemically inert pollutant) as a
function of air exchange rate and time.
where C is .concentration at time t, C is initial concentration at time
t = o, Q is the air turnover rate (ft^/min), V is room volume (ft^), t is
time (min),,K is a constant to adjust for imperfect mixing, and Q/V is the
air exchange rate. Using a mixing constant of 1/2 they showed that pollutant
concentrations would decay in one hour to 61 percent of original con-
centration if the air exchange rate is once per hour, to 37 percent.
original concentration if the air exchange rate is twice per hour, and
to 5 percent if the air exchange rate is six times per hour.
These theoretical concentration decay rates (and others for
different time periods) were compared with actual measurements of concen-
trations made after controlled indoor releases of aerosol sprays containing
halogenated hydrocarbons. Decay rates of concentrations of vinyl chloride
and Freon 12 in a closed room showed concentration decay patterns approxi-
mately the theoretical pattern in form. The decay of vinyl chloride
roughly paralleled that of Freon 12, suggesting that vinyl chloride was
chemically stable during the periods of measurement (up to 2-1/2 hours).
-127-
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When hairspray and deodorants were released the concentrations
in the breathing zone during spraying were 122.7 ppm for vinyl chloride
and 62.1 ppm for Freon 12. One hour later both concentrations had
reduced to about 0.1 ppm. Using an insect spray the immediate breathing
zone concentrations were 380.1 ppm for vinyl chloride and 466.4 ppm for
Freon 12. One hour later the concentrations were 0.8 ppm and 0.9 ppm
respectively [86].
These authors also reported upon concentration of perchloroethylene
used in aerosol spot removers, estimating possible concentrations as high
as 100 ppm immediately following spraying. They also noted the occurrence
of carbon tetrachloride in an indoor residential environment near a solvent
recovery plant, finding a peak measurement of 90 ppm - peak duration was
not specified [86].
4.7 PARTICULATES
Indoor particulate behavior investigations have sought not
only to report mass-weight concentrations but to describe the particles
by their origins and chemical constituents.
Primary particulates are particles injected directly into the
atmosphere as a result of chemical or physical processes peculiar to
any emission source. Common sources are windblown soil, industrial
emissions, and combustion systems. Examples of typical primary particulates
are pollen, fly ash, the mixtures of combustion wastes often called "soot,"
and the mixtures of various particulates called "dust." Secondary particu-
lates are formed as a direct result of atmospheric reactions involving
-128-
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gaseous species such as S02, NOX> 02> NH3> H20, and hydrocarbons [209].
They range from 0.01 to 1.0 ym 1n size and are typically sulfates, nitrates,
or hydrocarbons. The classification of partlculates as primary or secondary
1s helpful 1n determining the origin of ambient partlculates, 1n describ-
ing their behavior, and 1n determining control strategies. This classifi-
cation however 1s of limited value 1n describing indoor pollutant behavior
and appears not to have been used to characterize airborne partlculates
Inside buildings.
Particle size characteristics are important in the study of
particulate behavior. Particulates may consist of "a cluster of several
molecules or they can be as large as visible dust kernels" [209]. Par-
ticles larger than 5 ym can be sized directly using screens or sieves
which measure the geometric or physical size of particles, according to
Fennelly [209]. Impingers are used to determine the aerodynamic equivalent
diameter of particles in the size range of 0.1 to 5.0 ym. Finally,
particles smaller than 0.1 ym must be monitored using the optical or
electric properties of the particle [209],
The importance of particle size to indoor particulate behavior
is twofold. First the size of the particles determines both their ability
to infiltrate and diffuse into the indoor environment and their trans-
port and decay within rooms and floors of dwellings and buildings.
Secondly, the size of particles determines the extent to which they
pass various stages of the human respiratory system. Fennelly [209]
points out that primary particulates ("particulates that are injected
-129-
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directly into the atmosphere") comprise the bulk of particles greater
than 2.0 vim and that secondary partictilates ("formed as a result of
atmospheric reactions involving gaseous species") comprise a large
portion of the particles and behave much like a gas by being subject to
Brownian movement, following fluid streamlines and capable of coagulation
and condensation.
The chemical behavior of particulates may be determined by an
analysis of individual particles and by the types of gases which can
absorb onto the particulates surfaces. Investigations of trace metals
in fly ash and urban air indicate that such toxic elements as Pb, Mn,
Cd, Tl, As, Ni, and S increase in concentration with decreasing particle
size [155, 381]. Tables 25 and 26 adapted from the work of Lee and
Van Lehmden [381], which show the concentration and size of trace metal
1n urban air and 1n fly ash as a function of size, appear on the following
page. This information applies to the ambient air, but would also be
relevant to infiltrated ambient air entering buildings.
The constituents of particulate matter, including sulfates,
nitrates, polycyclic organic matter, and asbestos, have been linked
with various chronic diseases [566, 567]. There is a growing consensus
that although size, shape and solubility of a particulate determine its
deposition in the human respiratory system, the chemical nature of the
particulate determines its toxicity.
Few studies have been conducted in indoor particulate behavior
in which both the size and chemical constituents of the samples have
been determined. Studies by Jacobs et al. [329, 330] of dust counts
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TABIE 25. CONCENTRATION AND SIZE OF TRACE METAL
PARTICLES IN URBAN AIR [38l]
Metal
Fe
Pb
Zn
Cu
Ni
Mn
V
Cd
Ba
Cr
Sn
Mg
Concentration,
M8/m
0.6-1.8
0.3-3.2
0.1-1.7
0.05-0.9
0.04-0.11
0.02-0.17
0.06-0.86
0-0.08
0-0. 09
0.005-0.31
0-0. 09
0.42-7.21
MMD*, fim
2.35-3.57
0.2-1.43
0.58-1.79
0. 87-2. 78
0.83-1.67
1.34-3.04
0.35-1.25
1.54-3.1
1.95-2.26
1.5-1.9
0.93-1.53
4.5-7.2
Particles
-------
and suspended participate, report that the mass-weight of participate
and its average size in indoor air are not significantly different from
that of outdoor air. Yocom et al. [716] suggest that particulate can
become enriched with soluble organic matter. Their data demonstrate
that the relative enrichment of indoor particulate matter with respect
to soluble organic material is a result of the generally small size of
these soluble organic particles and the presence of sources for this
enrichment indoors (smoking and cooking). Investigators have found
that the organic portion of particulate is higher indoors than outdoors,
whereas the ash content of particulate is higher outdoors [241].
Particulate resulting from cigarette smoking is no longer
considered to be just a personal health hazard, but a danger, in varying
degrees to the nonsmokers who occupy the same general area [486]. The
Federal Aviation Administration's 1971 report on "Health Aspects of
Smoking in Transport Aircraft" [662] found that cigarette smoke is the
primary contaminant on passenger aircraft. Elliott and Rowe [185]
reported that smoking at public gatherings leads to a five-fold increase
in the average total suspended particulate matter over the normal back-
ground level. The authors also reported that where enforcement of "No
Smoking" regulations is in effect there is a significantly lower level
of suspended particulate matter (SPM).
The size of particulates in tobacco smoke ranges from 0.01 to
1.0 ym [208], This is of particular concern since particles in this
range can be deposited in the lung. The particulate matter in tobacco
smoke remains suspended and, like a gas, diffuses within an Indoor
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environment. It has also been reported that the participate concentration
level which results from the "smoking of one cigar completely overcomes
the effect of the filtration device (electrostatic filter) for at least
one hour and the counts are still well up at the end of two hours" [382].
After smoking takes place there is a high concentration of SPM
in the room which decreases with time, as the ventilation system and
other mechanisms remove particulates. The rapid rise in the concentration
and the slow removal of particulates can be averaged to obtain the decay
rate in terms of a half-life. Because of the differences in half-lives
between CO and SPM, CO cannot be used as a tracer for SPM without the
use of a correction factor [486]. Also the use of CO as a tracer to
define the behavior of cigarette smoke was found to be unsatisfactory
by Hinds and First [296]. The authors determined that nicotine was a
better tracer since tobacco is virtually the only source of nicotine
and it is the second largest component of tobacco smoke particulates.
Penkala and de Oliveira [486] found that the-half-life of SPM is 42.8 min
from cigarettes and that the smoking of one pack of cigarettes per day
will raise the particulate concentration in occupied spaces above the
ambient air quality annual standard (75 yg/m ), and above the 24-hour
standard (260 ug/m3) in all but the best ventilated conditions. Bridge
and Corn [88] also concluded that suspended particulate matter generated
from cigarette and cigar smoking can reach concentrations considered to
be excessive in comparison with the annual ambient air quality standard
arithmetic mean. A later study by Hinds and First [296] obtained resif ":s
which were lower than those of Bridge and Corn, who did not allow for
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evaporative and diffusive losses to surface areas. Hinds and First con-
cluded that "although tobacco smoke concentrations often exceed the
annual average air quality standard for clean air, these levels would
not be expected to produce the strong public reaction to tobacco smoke
that has developed in the past few years. This observation suggests
that annoyance from tobacco smoke is caused by factors other than the
average concentration of particulate matter in the indoor atmosphere.
For example, annoyance may be a response to peak concentrations of
tobacco smoke that are likely to be much greater than the average values"
[296].
4.8 OTHER POLLUTANTS
There have been several studies of mercury vapor behavior in
buildings, examining sources such as fungicides in latex wall paints,
broken mercury thermometers, or laboratory emissions (from incomplete
cleanup of spilled Hg) [217], A study on the mercury emissions from latex
paints [570] reported interior background levels of mercury of 0.32 yg/nP.
The same study found Hg levels during painting (latex paint) of 4.5-
12 yg/m3 with a decay rate after 10 days of 3.5 x 10" percent/day. They
estimated that the mercury vapors would last for approximately seven
years [570].
Pesticides have been reported in various concentrations in
the indoor environment attributed to both infiltration from the ambient
air, and indoor use of common household aerosol insecticides. Davies
et al. 1975 [151] reported average DDT concentrations of 129 ppm from
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samples taken from 15 homes. In one home there was a peak level of
916 ppm of DDT. Davies also reported levels of Dieldrin at 29.3 ppm
and Methoxychlor of 212 ppm. Another mechanism for pesticide contamination
of the indoor air can take place as a result of the vaporization of pesti-
cides which have been applied in a liquid or solid state. Leary et al.
[379] found concentrations of DDVP as high as 0.13 mg/m^ in the air of
Arizona homes several days after installation of polyvinyl chloride resin
strips. This level declined to 0.08-0.09 mg/nv* between two and four weeks
after installation.
4.9 OVERVIEW OF RESEARCH IN THE DISTRIBUTION AND BEHAVIOR OF INDOOR
AIR QUALITY
The concentrations, residence times and decay rates of the
major ambient air pollutants, S02, NO, N02, CO, 03 and suspended par-
ticulates, have been studied in indoor environments by a number of
researchers. The role of building ventilation in establishing indoor/
outdoor concentration ratios has been investigated. Data are to some
extent available to assist in deriving correlations and testing the
validity of models which describe the physical behavior of all these
pollutants as they enter, remain in, and leave the indoor air environment.
The data available will permit only gross generalizations concerning the
movement of pollutants (i.e., pollutant concentration gradients) within
structures. Researchers have measured their concentrations "inside" and
"outside" the structure; sometimes "in a bedroom" or "in a kitchen."
In some cases, distances are given between pollutant sampler locations
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and potential pollutant sources, but the amount of concentration data
precisely located in space and time with respect to measured emissions
sources in the indoor environment is small.
There are research data on the indoor decay of introduced
ambient reactive pollutants, which show correlations between removal of
pollutants from the air and such elements of the indoor environment as
temperature, humidity, presence of other reactive pollutants in the air,
room volumes and room surfaces. The data show positive correlations
between pollutant decay and these elements. There appears not to have
been research dealing with the formation in the indoor environment of
measurable quantities of such secondary pollutants as sulfates, nitrates
and nitrosamines. In general, the area of chemical transformation and
fate of indoor pollutants has not been addressed in depth from a chemical
modeling point of view; an exception has been the indoor behavior of
ozone as studied by Shair and others [561, 171].
Tobacco smoking has been the subject of much investigation.
There are data on pollutant emissions by species and quantity, and
there is a substantial body of measured indoor CO concentration and
particulate data associated with information about smoking as a source.
There is considerable literature dealing with the presence
in indoor air of other pollutants, among them halogenated hydrocarbons,
asbestos, mercury and other trace metals. But reports of measured
indoor air concentrations of these pollutants, or of their measured
source strengths, have not appeared often in this literature research.
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Section 5.0
MONITORING TECHNOLOGY
Indoor air pollution monitoring must rely heavily on ambient
air and industrial hygiene sampling technology. As these methods are
incorporated into indoor air sampling programs, changes must be made
in order to meet more stringent noise and space requirements. Ambient
air samplers such as hi-vols will have to be replaced by quieter and
smaller particle samplers. Additionally, for indoor sampling, consideration
of the volume of air removed from the structure must be taken into
account in order to avoid introduction of error with respect to the
natural ventilation rate of the structure. For example, a structure
with 30,000 ft volume may have a natural ventilation rate of 250 ft3
per min. Sampling air from this structure for test purposes through
several sampling lines may amount to as much as 12 to 15 cfm which must
be considered while developing indoor-outdoor numerical models.
Many other parameters relevant to sampling cannot be over-
looked. Those which appear to be of greatest importance are listed
below:
Sampling line material
Retention time within sampling line
Reaction of pollutants within sampling line
Response time of the continuous monitors
Sampling pump and manifold materials
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Avoidance of problems resulting from physical
constraints, I.e., water vapor condensation during
winter sampling periods
t Strict quality assurance procedures.
The purpose of this phase of the survey was to gather Informa-
tion on the sampling for and analysis of pollutants expected to be found
Indoors 1n dwellings and public buildings. Methods of sampling and
analysis and related Information such as detection limits and collection
efficiencies were sought. A literature search produced much information
concerning the monitoring of the six primary (criteria) pollutants was
readily obtained. Also examined were literature articles detailing
procedures for collection and analysis of the following nonprlmary
pollutants:
Metals (in general) in suspended particulate
Cd in particulate
Al 1n partlculate
Pb 1n settled household dust
Hg (particulate and gaseous)
Aerosol propellants
Ammonia
Pesticides
PAN
t Soiling particulate.
Information on the available monitoring technology for various
indoor air pollutants is presented in the following pages, categorized
by pollutant species.
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5.1 SULFUR DIOXIDE AND SULFATES
5.1.1 Sulfur Dioxide
Sulfur dioxide ($02) is a common atmospheric pollutant pro-
duced by combustion processes. Fossil fuels, such as coal and petroleum,
contain elemental sulfur, and when the fuel burns, the sulfur is converted
to sulfur dioxide and to a lesser degree, sulfur trioxide. Since fossil
fuels are burned abundantly in the United States to heat buildings and
to generate electric power, pollution of the atmosphere with the oxides
of sulfur is widespread and is especially prevalent in cities. Petroleum
refineries, smelting plants, coke processing plants, sulfuric acid manu-
facturing plants, coal refuse banks, and refuse burning activities are
also major sources of sulfurous pollution. Indoor concentrations of
SOg have been found in numerous studies to be related to that of the
outside air [27, 65]. Yocom has shown that furnaces in homes heated
by coal are also a possible source of high indoor S02 concentrations
[714, 716]. Recent work by Hollowell found elevated indoor S02 levels
associated with gas stoves [308],
Many instruments capable of continuously measuring ambient
concentrations of S02 are available commercially [375, 608]. These
instruments are based on different measurement principles with the most
common principles of operation being conductometrie and gas chromato-
graphic [375, 608]. Continuous analyzers using these principles have
been used for many years and have been thoroughly tested under field
conditions [65].
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Indoor-outdoor comparison measurements requires locating
Individual monitors at each sampling point, representing a substantial
equipment investment, and resulting in multiple servicing and space require-
ments with a lack of confidence in the comparison of data from point to
point [691]. The use of a single instrument with a multiple sequencing
device has been found to be the most practical and economical approach
to the problem [715, 308, 691]. Yocom describes a unique mobile measure-
ment system capable of sampling at four locations using a single instru-
ment for each parameter [715, 716, 691]. This system consisted of four
continuously purged sampling lines with an integrating chamber and solenoid
switching valves. By drawing the instrument's air sample from the inte-
grated sample chamber, retention time was reduced to approximately two
seconds. The short retention time allowed four 5-minute samples to be
sequentially measured with a conductometric S02 analyzer every 20 minutes.
In studying combustion-generated pollution In six homes,
Hollowell used an UV fluorescence S02 analyzer in conjunction with a
sequential sampling system to make Indoor and outdoor measurements
[308]. The sample Intake for the gas and electric stove measurements
was placed 1n the breathing zone 1.5 meters above the floor near the
front of the stove.
Bubblers consisting of absorbing reagent and air flow measur-
ing devices have been used extensively in ambient air and industrial
hygiene to collect integrated S02 samples. These methods have been
Incorporated as standard measurement techniques by both the Environmental
Protection Agency and the National Institute of Occupational Safety and
Health [203, 649].
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Dynamic calibration of sulfur dioxide monitors Is considered
to be the most desirable technique as opposed to calibration by static
means. Dynamic calibration is normally accomplished by employing one
of two basic techniques:
Dilution of sulfur dioxide gas mixtures with "zero"
air followed by analyses employing the EPA Reference
Method [182].
The use of NBS certified sulfur dioxide permeation
tubes and related zero air dilution apparatus [475,
541, 542]. '
The technique employing dilution of the standard gas mixture
and simultaneous analyses by the reference method requires considerably
more effort and time as compared to the use of the permeation tube
technique. Both methods can result in the same accuracy and precision,
but due to the increased number of operations inherent to the dilution
technique the permeation tube methodology has received wider use.
5.1.2 Sulfates
Airborne sulfates, like nitrates, have both natural and
man-made sources. Natural producers include volcanic action and
suspension of magnesium sulfate from sea spray [208]. Combustion of
sulfur-bearing fuels and smelting of sulfide ores are major non-natural
sources [550]. Combustion would seem to be the major indoor-generated
source of sulfates; intrusion of external air would also contribute.
One study, which Included particulate sulfur, measured 1t
by X-ray fluorescence [308], Studies of outdoor suspended particulate
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used the same method of collection as for nitrate, filtration followed
by water extraction. The analytical methods are those for sulfate in
water, and Include precipitation as barium sulfate, barium sulfate
turbidimetry, specific ion electrode, and methythymol blue colorimetry
[20, 475, 378].
5.2 CARBON MONOXIDE
Carbon monoxide (CO) is by far the largest single gaseous
pollutant found in urban atmospheres [557]. It is a product of the
incomplete combustion of all types of .carbonaceous fuels. Indoor CO
is generated by combustion processes such as smoking, heating, and
cooking [715]. Being nonreactlve, CO readily penetrates all structures
and Indoor concentrations are strongly Influenced by that of the ambient
air outside.
Of the six methods used to measure carbon monoxide,(Gas
Chromatography with flame ionlzation detector, Dispersive Infrared,
Nond1spers1ve Infrared, Catalytic Oxidation, Amperometric, and Mercury
Vapor), the nondlsperslve Infrared (NDIR) technique is the most popular
instrument used [375], This instrument is also the basis of the reference
method specified by the Environmental Protection Agency [203]. Yocom
used a nondlsperslve infrared (NDIR) instrument in conjunction with a
special sequencing sampling system previously described to measure
pollutant profiles Inside and outside of structures [715, 716, 691].
In his study of Indoor and outdoor concentrations, Derham et al.
used two NDIR instruments to simultaneously measure Indoor and outdoor
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CO concentrations [158], One instrument was located in a room of a
laboratory building, the other at the ventilation intake duct in the
same building. By this method Derham insured that the concentration
of the air actually entering the vent system would be measured. Thompson
incorporated a continuous NDIR analyzer and grab samples to do compara-
tive measurements of indoor-outdoor CO concentrations for 11 buildings
in the South Coast Basin of California. The NDIR analyzer was located
in a small house trailer near the building to be monitored and was
used to continuously measure the outside air. Grab samples were then
collected 1n Mylar bags from different locations within the building
and brought to the NDIR analyzer to determine CO concentrations.
The nondispersive infrared analyzer has also been found to be
a reliable instrument in the measurement of CO concentrations on..board
nuclear powered submarines [529]. While most studies on indoor CO
levels were conducted on residential homes or private buildings, Elliot and Rowe
carried out CO measurements 1n an area during public gatherings [185],
Measurements of CO were carried out by use of indicator tubes This
technique provides a simple and economical method of sampling but is
only useful for spot-checking CO concentrations. With a sensitivity
of ± 25 percent this technique is not recommended for indoor monitoring.
There are a number of ways of preparing CO gas standards [548].
for dynamic calibration of carbon monoxide analyzers. Most methods
Involve dilution of CO with a nonreactive gas of zero or known CO content.
This can be done using pressurized tanks [20] for large amounts or
plastic bags [548] if lesser amounts of standard gas are required.
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Standard gases are also commercially available and any concentration
can be specified and certified by the manufacturer [682].
There have been instances where purchased CO standards
have been in error [410]. For this reason it is important to compare
standards from independent sources to make independent determinations
of the CO concentration.
Presently, standard gases contained in specially treated
aluminum cylinders under pressure are in the widest use.
5.3 CARBON DIOXIDE
Carbon dioxide, a normal component of air, is a part of
the carbon cycle in the biosphere. In addition to occurring
naturally, it is produced in the combustion of fossil fuel. Since
humans also exhale carbon dioxide during normal breathing, indoor
concentrations have been found to be higher than those found
outdoors [65].
COp 1s normally not considered a pollutant and very little
work has been done in this country concerning indoor measurements. Stern
describes a nondispersive infrared spectrometer similar to those used
for CO measurements as a reliable method of continuously measuring C02
concentrations [606]. Integrated C02 sampling methods where the air
sample is bubbled through a reagent was also described. Two areas in
which C02 is a major concern are submarine atmospheres and atmospheres
in manned space craft. In both cases, a system employing mass spectrom-
eters has been developed to continuously measure C02 along with other
gases [527, 530, 529].
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Such multi-gas sensors could be very useful 1n future indoor
air pollution work.
There are a number of ways of preparing C02 gas standards [548]
for dynamic calibration of carbon dioxide analyzers. Most methods Involve
dilution of C02 with a nonreactlve gas of zero or known CO- content.
This can be done using pressurized tanks [20] for large amounts or
plastic bags [548] 1f lesser amounts of standard gas are required.
Standard gases are also commercially available and any concentration
can be specified and certified by the manufacturer [682].
There have been instances where purchased standards have
been in error [410]. For this reason it is important to compare
standards from independent sources or make independent determinations
of the C02 concentration.
Presently, standard gases contained in specially treated
aluminum cylinders under pressure are in the widest use.
5.4 NITROGEN OXIDES AND NITRATES
5.4.1 Nitrogen Oxides
Oxides of nitrogen are one of the most important groups of
atmospheric contaminants in many communities. They are produced during
the high-temperature combustion of coal, oil, gas, or gasoline 1n power
plants and Internal combustion engines. The combustion fixes atmospheric
nitrogen to produce the oxides. At these temperatures, nitric oxide
forms first and 1n the atmosphere it reacts with oxygen and 1s converted
to nitrogen dioxide. While this oxidation Is very rapid at high
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concentrations, the rate Is much slower at low concentrations. In
sunlight, especially 1n the presence of organic material as typified
by Los Angeles-type photochemical smog, the conversion of nitric oxide
to nitrogen dioxide 1s greatly accelerated.
Indoor concentrations of NO have been found to be related
A
to Indoor combustion sources used for heating and cooking and to
the outside ambient concentrations [308, 691, 431, 385, 627, 158].
In order to make comparison measurements between Indoor and
outdoor N0-N0x gas analyzers [158] simultaneous measurements were taken
by locating one analyzer In a room of a laboratory building and the other
next to the ventilation Intake duct on the roof of the same building.
It was felt that this method assured that actual concentrations of
NO-NOX in the air entering the vent system would be measured. In this
way the relation between NO-NO entering the building and the Indoor
A
concentrations could be compared.
Hollowell, In making comparative measurements, utilized a
single chemiluminescence analyzer to measure NO/N02/NOX [308]. By
locating the Instrument near the Indoor and outdoor sampling locations
and using a multi-point sampling system, samples could be collected
at both locations. The sample Intake for gas and electric stove
measurements was placed in the breathing zone approximately 1.5 meters
above the floor near the front of the stove. Measurements to study
the effects of the heating systems were made with the sample Intake
in the bedroom approximately 1 meter above the floor.
Yocom determined indoor-outdoor pollutant profiles with a
single chemiluminescent analyzer and a mobile multiple point sequential
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measurement system [715]. Sample lines were run from the equipment to
four sampling stations. One station was located outside the structure,
the other three being in the kitchen, living room and bedroom. Sample
intakes for each station were placed in the breathing zone, between
4-1/2 and 6 feet above the floor. The sample inlet in the kitchen
was placed adjacent to the stove. By sequentially taking 5-minute
samples at each location short-term effects of stove use on indoor
air quality and pollutant behavior within the structure could be
studied.
When making comparisons of indoor-outdoor NO and N02 con-
centrations for 11 buildings in the South Coast Basin of California,
Thompson made use of both continuous and grab samples [627]. A continuous
N0«-N0 analyzer along with other instruments and accessory equipment
£ /\
were Installed in a small house trailer. The trailer was set up
near each building to be sampled and the N02-NOX monitor used to
continuously measure the outside ambient air. Indoor grab samples were
then collected in ffylar bags and brought to the N02-NOX monitor for
analysis. In studies where NO emissions from natural gas-fired
A
appliances were studied, continuous chemiluminescent NOX analyzer
and 24-hour integrated bubbler samples, determined with the Jacobs-
Hochheiser method, were used [431, 385].
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Dynamic calibration of oxides of nitrogen monitors, specifically
chem1lum1nescence analyzers which are in most prevalent use today, are
normally calibrated by one of the three following techniques:
t Dynamic dilution techniques employing certified
concentrations of NO or N02 in nitrogen contained in
treated aluminum cylinders under pressure. With this
technique the NO or N0£ gas is diluted with zero air
and the resulting mixture Is Introduced to the monitor
through a manifold system [182]. With this technique
for NO gas, there exists the possibility of oxidation
of NO to N02- Should this reaction occur the amount
of NO oxidized to N02 would be detected by the N0?
analyzer.
Certified NBS NO? permeation tubes and a related dilution
system has also found broad usage for the dynamic
calibration of nitrogen dioxide monitors.
t Gas phase titration [186] employing certified NO gas
concentrations as one of the gaseous reactants and
a stable source of ozone as the other 1s employed to
produce varying levels of known concentrations of NO
and N02, based on the following reaction:
NO + 03 -> N02 + 02, K = 1 x 107 mole"1 sec"1
Both NO and NCL monitors can be calibrated simultaneously
with this technique.
Of the three techniques referenced above, the gas phase titration
is at present being used more frequently due to the fact that both parameters,
I.e., NO and N02 can be calibrated against a standard which is traceable
to NBS.
5.4.2 Nitrates
Several sources contribute nitrate to the environment. Natural
sources include oxidation of atmospheric nitrogen by soil bacteria and
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lightning, and discharge by volcanic action [557]. Humans add nitrates
by combustion processes and application of fertilizer. Combustion appears
to be the major source of indoor nitrate; it is possible that bacteria
in household plant soils oxidize combustion generated NOX as well as
elemental nitrogen [62].
No major studies on nitrates in indoor air have been published.
Some work has been done on their presence in fugitive dust [495],
Generally, particulates are collected on a filter medium,
and the water soluble portion leached out. Nitrate in water can be
determined by the phenoldisulfonic acid (PDSA) method, the brucine
method, or by use of a specific ion electrode [19, 25, 475]. The
methods have different sensitivities and interferences, so the choice
must be made according to expected levels and other ions present.
5.5 PHOTOCHEMICAL OXIPANTS
Ozone is one of the principle oxidants found in photochemical
smog - a major air pollution problem arising from atmospheric reactions
of gases derived from the combustion of organic fuels. Emissions from
motor vehicles are a prime factor in the formation of photochemical
smog in virtually all parts of the country. Other factors which contribute
to smog formation are the combustion of fuels for heat and electric power,
burning of refuse, evaporation of petroleum products, and handling and
use of organic solvents. Ozone is also formed naturally by electrical
discharge (lightning) during thunderstorms and the reaction of ultraviolet
on oxygen molecules.
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Very little ozone is generated within a structure; it is
generally brought in with the outside air [626, 627]. Being highly
reactive, ozone levels inside structures were generally found to be
1/2 to 2/3 of those In the ambient air outside.
Although a considerable amount of work has been done in
measuring outdoor ozone concentrations, very few indoor measurements
have been made. This is probably due to the fact that ozone is highly
reactive and therefore 1s easily removed from the indoor air [626,
158, 627].
Thompson, 1n his measurements of ozone levels inside of a
hospital, used an ozone meter based on the electrolytic Brewer cell
[626], Calibration of this instrument was done by comparison
of concentration simultaneously measured with a solution of buffered
potassium iodide. A further check of the instrument's accuracy
was made by comparing its results to measurements obtained by the
absorption of a standard atmosphere of ozone 1n a long path infrared
spectrophotometer. Details of measurement locations were not presented
1n the paper. In a later study, Thompson used two of the previously
described ozone meters to make comparisons between Indoor and outdoor
ozone concentrations [626].
Ozone, while not being considered an indoor generated pollutant,
was measured In a study on combustion-operation indoor air pollution
conducted by the Lawrence Berkeley Laboratory [308]. A UV absorption
unit was used to measure any ozone that might be produced under typical
occupancy conditions of cooking and heating. As expected, except for
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a small increase in ozone during usage of the electric stove, no
combustion-generated ozone was found.
Analyzers employing chemiluminescence, electrochemical and
spectrophotometric gas phase techniques have been used to continuously
monitor ozone. Only analyzers that meet EPA Ambient Air Quality Reference
and Equivalent method standards should be employed in indoor air
monitoring [65].
Dynamic calibration of ozone analyzers requires a stable
source of ozone. Such a source has been developed [78] and is
commercially available. The ozone generator (source), however, requires
calibration. Three techniques are presently in wide use. They are:
The Neutral Buffered Potassium Iodide method [682]
§ The gas phase titration technique employing NBS
certified NO gas as the reference material
The reverse gas phase titration technique employing
NBS certified NO gas as the reference material and
related apparatus for complete reaction of 0, with
the N02 which is initially formed [186].
Of the three techniques stated above, the Neutral Buffered
Potassium Iodide method is employed most frequently, since the
other techniques require a nitrogen oxide analyzer as an integral part
of the calibration apparatus or other special gas apparatus for the
reaction chambers. In those instances where both ozone and nitrogen
oxide analyzers are to be calibrated, the method of choice is the gas
phase titration.
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5.6 HYDROCARBONS
5.6.1 Total Hydrocarbons
Hydrocarbons are a group of compounds made up of carbon and
hydrogen atoms. These are emitted during the incomplete combustion
of all fuels (including rubbish and agricultural field wastes), but
automobile exhaust 1s the major source. Hydrocarbons and other
organic gases are also expelled during the production, refining, and
handling of gasoline and from such manufacturing operations as industrial
dryers and ovens, and furnaces used for baking paints, enamels and printing
Ink. Indoor generated sources are heating, cooking, and solvent usage
[158].
Sampling of indoor air for HC presents no unusual problems.
While there are different monitoring methods available for HC, the
method recommended is that specified by the Environmental Protection
Agency. This method involves filtration through a 3 to 5 micron
filter before Injections of the sample into a flame ionization detector.
To determine nonmethane hydrocarbons, an aliquot of the same sample is
Introduced Into a stripper column which removes water, carbon dioxide,
and hydrocarbons other than methane. The remaining methane is then
measured by the flame ionization detector. The difference between
total HC and methane gives the HC that is of concern as an air
pollutant [607]. The non-dispersive infrared spectrometry technique
based on the broadband absorption in the wavelength region of a few
micrometers has also been used for THC measurements. This technique
is subject to interference because other bases (HgO, C02) absorb at the
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wavelength of Interest [375], Gas chromatography serves as a useful
tool 1n HC measurements, in that individual hydrocarbon components
can be identified [375].
Dynamic calibration of total hydrocarbon and methane monitors
can be performed by several techniques. These techniques include dilution
systems employing the desired hydrocarbon and a zero gas for dilution
air [645], a permeation tube containing the specific hydrocarbon which
has been gravimetrically calibrated [475] and an appropriate dilution
apparatus, or Inert plastic bags filled with known volumes of zero
air and the appropriate hydrocarbon [182]. Calibration gases are
commercially available and their content can be specified with respect
to concentration and certified by the manufacturer to within ± 2 percent.
Recently [682] these standard gases have been shown to be stable for
long periods at low concentrations, which enables one to employ the
gas directly from the cylinder without dilution.
This latter source of calibration gas, for low molecular
weight hydrocarbons (C-, thru Cg), is being employed most frequently
at present.
5.6.2 Organic Solvents and Trace Organic Materials
Organic solvents are found in most homes; for example,
various cleaning fluids such as perchloroethylene, lighter fluid,
and fingernail polish remover contain assorted aliphatic, aromatic,
and chlorinated components. In addition, hobby materials such as model
airplane cement and varnish contain similar materials. Some solvents
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likely to be encountered are perch!oroethylene, toluene, and naphthas.
Gasoline fumes can penetrate from an attached garage.
Organlcs other than solvents are found in many homes. Primary
examples are the Freon propel 1 ants in spray cans, various Insecticides,
and nicotine from smoking.
Two studies, by Collins et al. and Compton et al., investigated
pesticides in homes [133, 136]. The former involved collecting vapor in ethyl
acetate, followed by concentration and analysis by gas chromatography.
The second used collection 1n several media, followed by a series of
aqueous and organic extractions to separate pesticides Into groups.
Two other studies Involved sampling and analysis for chlorofluorocarbons
(Freons); only Hester's Included sampling and analysis [288, 86], His
group collected air in standard glass sampling tubes and analyzed
It by gas chromatography. Detection limits of Freon 11 and 12 were
5-10 ppt and 100-200 ppt, respectively. Two other groups studied
nicotine 1n Indoor air [296, 312]. Hinds collected tobacco smoke
on Millipore filters, extracted the nicotine with water, and analyzed
by gas chromatography. Morning's group analyzed air with a mass
spectrometer.
One of the most widely used methods for organic vapors in air
1s collection in tubes of activated charcoal, desorption Into an
organic solvent, often carbon dlsulflde, and analysis by gas
chromatography. The method has been used outdoors and 1n Industrial
applications [645, 550, 514, 690, 362]. Elfers achieved a detection limit
of 1-10 ppb when sampling 250 1 of air through 13 cm of charcoal [183],
-154-
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Studies in the laboratory have determined the collection
efficiencies of chromosorb 12, followed by hexane-acetone extraction,
and ethylene glycol with a benzene extraction [624, 423]. Both
sets of analyses were made by gas chromatography.
The major problem involved with any pesticide analysis is
contamination; the chromatograph must almost always be used only for
pesticides. The same restriction applies to the sampling and analysis
of Freons. The analysis of the more common organic solvents is not so
difficult because their levels are usually above the noise of a slightly
dirty chromatograph. Large samples can be taken by using long (15 cm)
charcoal tubes and high sampling rates, so long as the rate is not too
high to allow adsorption to occur.
5.6.3 Aldehydes
Aldehydes are a class of organic compounds, members of which
may be present in the indoor atmosphere. Some aldehydes are produced
from incomplete combustion during cooking; formaldehyde is a part of
the glue used as chipboard binder and is released from it over a period
of years [28].
Indoor studies of formaldehyde have involved sampling about
50 1 of air through a bubbler system into chromatropic acid solution,
followed by color development and spectrometric analysis [28, 686, 9].
Anderson's group attained a detection limit of 0.1 mg formaldehyde per
m, with a reproducibility of ± 5 percent at 1 mg/m3 [28].
Another procedure for aldehyde determination, which has
not been used on indoor air samples, is the MBTH (3-Methyl-2-Benzothiazolone
-155-
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Hydrazone Hydrochloride) method [276]. It involves sampling into a
solution of MBTH, followed by color development and spectrometric
3
measurement. A 50 1 sample has a sensitivity of 0.04 ug/m aldehydes
expressed as formaldehyde.
The MBTH method appears to be better than the chromotropic
acid method. It is more sensitive, and responds to all water soluble
aliphatic aldehydes; the chromotropic acid method responds to only
formaldehyde. The two procedures are about equally complex as far
as laboratory work. The WJTH method is not 100 percent efficient;
its efficiency can be determined under the exact conditions to be used.
Further research would include studies of collection efficiencies
under various flow rates and sampling times for both methods.
5.7 PARTICULATES
Particles of solid - and occasionally liquid - matter in
the air constitute an important portion of polluted community air in
most cities and towns in the United States. These so-called particu-
lates may be either so large that they rapidly settle to the ground or
they may remain suspended in the air until they are removed by such
natural phenomena as rain - or until they are inhaled by people.
Particulates may be quite complex in their chemical composition. The
organic materials found in airborne particles may contain aliphatic
and aromatic hydrocarbons, acids, bases, phenols, and other compounds.
Airborne particles may also contain any of a wide range of metallic
elements; those most commonly found are silicon, calcium, aluminum
iron, magnesium, lead, copper, zinc, sodium, and manganese. Sources
-156-
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of participates include such activities as fuel combustion, various
manufacturing and processing operations - including production of steel,
cement, and petroleum products, and open burning and incineration of
refuse. Particles found indoors which may be carried in with ambient air
or generated indoors are from cigarette smoking and resuspension of dust
by human activities (use of paper products, turning pages in books,
standing up, sitting down, and changing and brushing clothing [226]).
Cooking, heating, cleaning, and use of aerosol sprays are also known
sources [716, 308]. Buchnea and Buchnea report that air conditioners which
normally remove particles may generate aluminum oxide particles of
their own [94]. Indoor particle concentrations may be measured con-
tinuously or as integrated time-averaged samples. Most researchers
prefer to use the integrated method where particles are collected
(filtering, impactor, etc.) and then gravimetrically measured. The
main advantage of this method is that it is inexpensive and that particles
can be subjected to chemical and physical analysis at a later time.
Particle concentrations are normally presented as total suspended
particles (TSP) or respirable particulates.
5.7.1 Total Suspended Particulate
One of the most basic instruments for collection of total
suspended particulates (TSP) is the hi-volume air sampler. This instru-
ment, which pulls an air sample through an 8 x 10 inch filter at a flow
rate of 30 to 50 cfm, is widely used for ambient air sampling. Elliot and
Rowe used a hi-vol for making TSP measurements in an arena during public
gatherings [185]. One problem that Yocom and Thompson found in their
-157-
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studies was that the noise level of hi-vols was unacceptable in occupied
buildings [715, 626], In both cases special filter collection devices
were built. Yocom used a 4-inch filter holder with a Type A glass fiber
filter [715], The filter holder was connected to a vacuum line attached
to a pump. By locating the pump in a trailer outside the building the
indoor noise was minimized. Samples were collected over 12-hour periods
with approximately 100 cubic meters of air being sampled for each period.
In Thompson's case, a 9 cm diameter plastic Buchner funnel was modified
to use discs of the same diameter cut from glass-fiber hi-vol filters [626],
A gas meter and rotary pump were used to provide an air flow of 0.47 dubic
meters per minute through the filter.
When particles are collected for chemical analysis, care
must be taken to select the proper collection media. In the study of
combustion-generated indoor air pollution, Hollowell selected two types
of filters to be used to collect particles for chemical analysis [308].
For elemental composition by X-ray fluorescence a 1.2 NM pore size
cellulose filter was selected. Particle samples were collected on a
47 mm filter at a flow rate of approximately 70 1pm for 30 minutes.
A Selas Flotronlcs 5.0 NM pore size filter was used to collect
particles for Ionic species analysis by electron spectroscopy. A flow
rate of 70 1pm was used for a two-hour sampling period.
5.7.2 Respirable Particulate
In order to sample for respirable particulate some mechanisms
must be used to separate the respirable size particles from the total
particle loading. In his first attempt at measuring respirable
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particulates, Yocom used a polyurethane prefliter 1n accordance with the
method of Roesler [524]. Additional work on size discrimination was
carried out with two cascade impactors. This method proved to be effective
in determining the respirable size fraction of the TSP. Cascade impactors
were also used by Oesaedeleer to collect respirable size particles for
analysis by proton-induced X-ray emissions (PIXE) [161].
The Dlchotomous Sampler [488] is designed to sample airborne
particles and classify them into two size fractions. The heart of the
sampler is a two-stage virtual impactor whose principle of operation is
analogous to that of an inertia! Impactor; however, the problems of
particle bounce and shattering are eliminated. Particles above the cut-point
size flow directly through nozzles of two stages and are collected on a
filter at a rate of 1/50 of the sampling flow rate. The major fraction
of the air is deflected around the nozzles of each stage and flows
through a second filter where the particles smaller than the 50 percent
cut-point of the sampler are collected. The primary advantage of the
sampler is that the particles are uniformly deposited on low mass filters,
which is most suitable for the assessment of their mass and chemical
composition.
Fuchs, in his review of aerosol sampling, expressed concern
that sampling methods used may not give a true representation of the
air sampled [225]. He suggested a spherical probe tip whose surface
was pyramids, points out, so there are no flat surfaces facing out.
When the same problem was examined by Breslin it was found
that an open face filter of the type normally used to collect indoor
-159-
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air samples sampled correctly in calm air for the normal range of
operation [83]. While open face filters may be used for calm air,
sampling directly in air streams from ducts, air conditioners, or
furnaces presents a different problem. In order to get a representative
sample from a moving air stream, isokinetic sampling must be undertaken.
Gieseke, in work performed on techniques for evaluations of airborne
particulate matter, developed a sampling probe for use in sampling
return air ducts [238], With this method, air being sampled moves into
the probe at the same velocity with which it leaves the duct allowing
a representative sample to be collected. Three probes were used, two
for collecting TSP on filters and one for particle sizing with a cascade
impactor.
Many indoor particulates are generated by activities of people
and the concentration that a person may be exposed to during the day
is often much higher than that of the average indoor air. This would
be particularly true for housewives who are constantly being exposed
to dust from cleaning and cooking, while the overall 8 to 12 hour
-average concentrations in the house may remain low. Personal monitors
for respirable particulate have been shown to give good agreement with
other measurement methods and should prove to be a useful tool in health
effect studies [177].
One type of gravimetric sampling system which separates
respirable and nonrespirable dust consists of a portable pump with
an elutriator and filter in which the dust is collected. The
nonrespirable dust is collected in the cyclone (elutriator), and the
respirable dust in the filter.
-160-
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The elutrlator and filter are fastened to the person's
clothing near their breathing zone. In this manner the quantity of
dust that a person would actually breathe throughout the day can be
measured.
5.7.3 Trace Metals
Many metals can be found in the home. Some, for instance
lead, primarily enter from outdoor air. Others can be generated
Indoors. Principal contaminants to be expected are lead from automobile
exhaust, mercury from paint fungicides and aluminum from air conditioners
[217, 94], Specific household activities could contribute to
others. For Instance, antiperspirant sprays could add zirconium to
the air; home shops could suspend iron, zinc, aluminum, and lead dusts.
Many methods have been used to sample and analyze for airborne
metals 1n the home. Braman and Johnson describe a series of absorbers
to selectively trap different forms of airborne mercury; each absorbent
was analyzed by de-discharge spectral emission spectrography [80], Foote
collected mercury vapor on gold screens and analyzed for 1t by fTameless
atomic absorption [217]. Slbbett et. al [570] used an automated system
employing collection on a siver screen, vaporization, and ultraviolet
photometric analysis. Moffit and Kupel absorbed mercury vapor on
activated charcoal and analyzed for it using atomic absorption [434].
This last method had a detection limit of 0.02 ug in 10 1 of air.
Both Berdyev et al. and Vostal et al. examined the indoor
environment for lead [66, 671], The former sampled airborne particulate
and determined the lead content with the chromate method. Vostal's
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group, on the other hand, collected settled dust with damp paper towels,
leached them with add, and determined lead by polarography. Buchnea
and Buchnea found a high percentage of aluminum In both settled and
airborne dust, analyzing by 8-hydro*y qulnoline precipitation [94].
Several reported studies have been made of metals in outdoor
air partlculate; 1n general, they have employed high volume samplers
with either glass fiber or membrane filters, which are add leached
and the leachate analyzed by atomic absorption [438, 99, 685, 357, 321,
630]. Neutron activation analysis and X-ray fluorescence spectrometry
have also been employed [246, 723, 82, 487, 304, 516, 251, 105, 517,
515]. One study, however, addressed itself to the determination of metals
in low volume samples [62]. Polymer filters were acid leached and the
various metals determined by flameless (graphite tube) atomic absorption
spectrophotometry. The small amounts of the metals present necessitated
ultrapure reagents and scrupulously clean equipment.
The procedure used by Begnoche could certainly be applied
to Indoor studies. It Is extremely tedious, though, Involving a
considerable amount of acid washing of glassware, and costly ultrapure
reagents. Acid leaching of whatever filter type chosen, followed by
flameless or flame atomic absorption spectrophotometry, appears the
most versatile procedure for a wide variety of metals [62].
Mofflt and Kupel's activated charcoal mercury procedure
distinguishes between partlculate mercury collected on a prefilter
and gaseous forms In the charcoal [434], Collection on gold, as performed
by Foote, measures only elemental mercury vapor, and Braman and
-162-
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Johnson's sequential absorbents are too complicated for routine use
[217, 81].
Miniaturized continuous particulate samplers ("streakers")
have been developed [462] to collect particulate samples for elemental
analyses employing the proton induced X-ray emission (PIXE) analytical
method [462]. The streaker consists of an orifice which is driven with
a synchronous motor across a strip of nuclepore filter media at
a rate of approximately one inch per day. Vacuum is applied to the
orifice such that the restriction through the nuclepore filter at the
orifice is at critical flow conditions. The size of the orifice and
the porosity of the nuclepore filter have been chosen to result in a
sampling rate of 1 1/min. After sampling for one week the filter medium
is removed for PIXE analyses. The proton beam can be focused on the
filter material such that short (1/2 hour to 2 hour) increments of the
sampling period can be analyzed for as many as 10 elements simultaneously,
5.8 CONCLUSIONS
As a result of reviewing and evaluating the information
and data uncovered by this literature review, we have reached
a series of conclusions relative to the most appropriate complement
of methodologies and equipment currently available for indoor-outdoor
pollutant monitoring. Table 27 presents our recommendations for
the continuous monitoring program, including the pertinent performance
parameters of each system. Table 28 lists our chosen sampling and
analytical methods for indoor-outdoor monitoring of the nonprimary
pollutants of major interest to this investigation.
-163-
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TAB1E 27. CONTINUOUS MONITORING EQUIPMENT SPECIFICATIONS EMPLOYED FOR MONITORING INDOOR-OUTDOOR POLUJTANTS*
Pollutant
NO
NO
X
co2
CO
°3
j
so2
CH4
THC
Wind/Speed
Direction
Temperature
Relative
Humidity
Principle of
Detection
Chemilumi-
nesent
Chemilumi-
nesent
Nondisper-
sive Infrared
Nondisper-
sive Infrared
with flowing
ref. cell
Chemilumi-
nescent
Flame
Photometric
Flame loniza-
tion with
Selective TCH
Oxidizer
Flame loniza-
tion with
Selective THC
Oxidizer
Direction-
Syncho speed-
d.c. megneto
Bi-metallic
strip-temp.
Human hair
Concentration (ppm)
Range (s)
0-0.5
0-1.0
0-2.0
0-5.0
0-0.5
0-1.0
0-2.0
0-5.0
0-2,500
0-50,000
0-50
0-0.5
0-0.5
0-5
0-20
0-5
0-20
0-100 mp
0-540°
Adjust-
able
0-100%
Limit of
Detection
0.005
0.005
25
500
0.50
0.005
0.005
0.05
0.20
0.05
0.20
i 0.5 mph
5°
1°F
1% RH
Response Time to
90% or Greater
100 sec.
100 sec.
2.5 sec.
2.5 sec.
15 sec.
60 sec.
15 sec.
15 sec.
Precision
+ 1% Full
Scale
+ 1% Full
Scale
+ 1% Full
Scale
+ 1% Full
Scale
+ 2% Full
Scale
+ 1% Full
Scale
+ 1% Full
Scale
+ 1% Full
Scale
+ 1% Full
Scale
+ 1% Full
Scale
* Ranges, limits of Detection, Response Time to 90 percent or Greater, and Precision are specifications for particular models of continuous
instrumentation and will vary among manufacturers.
-------
TABLE .28. INTERMITTENT SAMPLING AND ANALYTICAL METHODOLOGY FOR INDOOR-OUTDOOR POLLUTANT MONITORING
Pollutant
Total suspended
particulates
Respirable
particulates
(3.5 y)
Organic
vapors
Alphatic
aldehydes
Ammonia
Sulfates from
TSP samples
Nitrates from
TSP samples
Lead from
TSP Samples
Elemental analysis
atomic No. 16
through 35 plus
No. 82
Sampling Rate
1/min
100
50
0.2
0.5
0.5
100
100
100
1
Sampling Period
hrs
24
24
-
24
4
1
24
24
24
Continuous
Analytical
Method
Filtration/gravimetric
Dichotomous/gravimetric
Cyclone @ 9 L/M
Charcoal absorption/
gas chromotography
Bubbler/MBTH
Bubbler/phenate
Filtration/me thyl-
thymol blue
Filtration/brucine
Filtration/atomic
absorption
Streaker sampler/
PIXE
Limit of De-
tection (working
0.1 yg/ffl3
0.1 yg/m3
ppb as CH .
1.5 ug/m3
5 ug/m
0.5 yg/m
0.1 yg/m
0.005 yg/m
ppb to ppt
o>
tJI
I
-------
Section 6.0
BUILDING OCCUPANCY
The levels of indoor air pollution are in large part a
function of the activities performed by building occupants, including
the control and operation of the building ventilation system by the
occupants. The building occupant determines, whether consciously or
not, an important part of the extent to which outdoor-generated
pollution is retained in the building. Many activities of building
inhabitants are in themselves pollutant-generating, for example:
sweeping, vacuuming, entering buildings with dirty shoes, use of
aerosol sprays, smoking, and breathing. Activities, mobility patterns,
various entrances and exits from the building, are all determinants
of indoor pollution levels. They are also determinants of the extent
of human exposure to indoor pollution, and hence of pollutant dosages
and the resulting health effects.
6.1 OCCUPANCY PROFILES
A first step in the investigation of indoor air quality is to
measure the duration of occupancy and the mobility of occupants. This
requires making detailed estimates of frequency, intensity, and duration
of human occupancy within the interior environment. Such estimates
normally take the form of occupancy profiles, where the rate of occu-
pancy is shown as a function of time. In a study performed by Seelye
et al. [555] occupancy profiles are shown for apartment houses and
elementary and high school buildings.
-166-
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MONDAY - FRIDAY-- WINTER
100
o
c
H
| 25
w
P.
i /I /i / / ;/ i
\/\''VV\/\>'\/
75 __ _.:. / £._!£_ ^ K .. . ! _
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5o-^;/-j^V- i:
1 2 3 l\ 5 6 7 8 9 10 11 ;i 1 2-3 4 .5 67-89 10 1112
MON. - FRI. - SUMMER
100 r,--
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\/\/\/\/\/\A/
1 2 3 ;i 5 6 7 S 9 10 11 i; i 2 3
5
7 8 9 JO 1.1. 12
WEEKEND SUMMER
100-
PI
D
75-
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FigureS. Apartment house. [555]
-167-
-------
100
WEEKEND - WINTER
o
52-.
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r>
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14
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t*
W
vvv
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1 23-!5 6? 8 9 10 11 N 1 2 3 V 5 6 .7 8 9 20 II12
Figure 8. Apartment house [ 553 J( Concluded)
CLASSROOMS
" 75
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WEEKDAY
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nrrixjm
1 2 3 *'> 5 6 7 3 9 10 11 21 1 2.3 ^ 5 6 7. 8 9 10 1.112
V/EEKDAY WITH LATE SHIFT
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12 3 Ji 5 6 7 S 9 10 11 II 1 23^ 56769 JO 1112
V/EEKDAY DURING BUSY SEASON
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1 2 3 ;i 'J C. Y C* 9 .V> :.''. i- 1 ^ 3 ;J
Figure 10. Shopping center. [ 555 ]
.7 89 jo :o. .1.2
-169-
-------
SATURDAY
J , , , .- { J .
o in o in o m o
o c- in CM o £- in
rt H
AONVdnOOO !M30H3d ' AONVdHDOO i
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Figure 10. Shopping center [555] (Concluded).
-170-
-------
Such estimates can be found in the literature for many building
types. Reported here are the occupancy profiles for apartment houses,
elementary and high schools and shopping centers, Figures 8, 9 and 10.
These profiles show occupancy as a function of time of day for various
building use modes relevant to the particular building type. For example,
profiles for an apartment house are given for weekday and weekend, for
summer and winter. The abcissa gives the hours of the day, while the
ordinate measures the intensity of occupation, in terms of percent of the
maximum occupancy for each particular building type.
Occupancy profile information can also be obtained from com-
puter models which use occupancy data to calculate building heating and
cooling loads. Figure 11 shows the occupancy profiles for residential
buildings used by two such programs. Both of these profiles show percent
occupancy as a function of time of day.
In contacting design professionals, it was found that occupancy
profiles are not often used in design work. The criteria which are
normally used in designing buildings include: the use to which the building
will be put (an office building will use different criteria than a super-
market); the maximum occupancy load of the building; how long, often and
at what time the maximum occupancies will occur; as well as the ability
to handle emergency situations (i.e., quick exits during fires) during
peak occupancy periods.
Building heating, cooling, and ventilating systems will be
designed to handle the peak occupancy levels and the specific temperature
and ventilation problems which can arise at these times. For example,
-171-
-------
o
o
o
UJ
Qu
1.0-
.75-
.50-
.25-
4 6 8 10 12 14 16 18 20 22 24
TIME OF DAY
SOURCE: NATIONAL BUREAU OF STANDARDS LOAD
DETERMINATION PROGRAM
PERCENT OCCUPANCY
1 . U '
.75-
.50-
.25-
h
1
4 6 8 10 12 14 16 18 20 22 24
TIME OF DAY
SOURCE: HITTMAN ASSOCIATES BUILDING ENERGY
ANALYSIS MODEL
Figure 11. Computer model occupancy profiles - residence.
-172-
-------
the cooling systems In a movie theater must be able to remove the body
heat of a full house while a movie is being shown. In a movie theater,
this occurs within well-defined time limits. In a residence, occupancy
does not always follow as strict a schedule of occupancy, but the body
heat of the people occupying a house at any point in time will usually
not be an overwhelming factor in the design of the cooling system. A
generalized occupancy profile, not specifying detailed time structure
of occupancy but based instead upon daily averages, will suffice for
HVAC system design.
6.2 HUMAN ACTIVITIES
The variety, frequency, and duration of human activities in
indoor spaces is an important factor necessary to adequately determine
indoor pollutant exposure. The occupancy profiles provide this for
occupants in the aggregate, but for individual pollutant exposure
studies it is usually necessary to collect this type of information
through subject interrogation.
A study by Chapin [117] reports the distribution of human
activities as a function of time. Results of this study are shown
in Figures 12 and 13. In each of these two graphs, the percentage of
persons engaged in a particular activity is shown as a function of time
of day. The activities shown hera, "sleeping," and "TV, rest and relax-
ation," are two which can easily be assigned to specific spaces within
a residence. The information collected in this study, as in most studies
of this kind, is in terms of types of activity, not in terms of locations
of activity within the building. Therefore, some assumptions must be
-173-
-------
UJ
_J
w>
t/1
o
.50
.25
o
a:
6 8 10 12 14 16
TIME OF DAY - WEEKDAY
Figure 12. Profile of persons sleeping [SOO].
18 20 22
TIME OF DAY - WEEKDAY
Figure 13. Profile of persons engaged in watching TV, rest, and relaxation [30°] .
24
0
X
0_J
tO UJ
S1*
a. a:
o
1 O
ry Q
t> '-'
a:
UJ Z
Q.*-«
l.Of
.75-
.50-
.25-
1 i . i
i 1
1 1
1
i
- ' r 1 1 i 1 1 i ' i i ' ~*
2 4 6 8 10 12 14 16 18 20 22 2
-174-
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made 1n order to find the time spent 1n various rooms of a house. For
example, 1t 1s clear that the activity "sleeping" usually occurs 1n the
bedroom. The activity "TV, rest, and relaxation" probably occurred 1n a
living room or family room.
Cooking, an activity which probably has a large impact on indoor
air quality, was not considered as a separate activity in Chapin's study.
Hittman Associates [301] developed a profile showing percentages of maxi-
mum appliance load as a function of time of day. This appears in
Figure 14. In this figure, a baseline of about 40 percent load represents
appliances that are used continuously, such as refrigerators and freezers.
The large peaks occurring in the morning, at noon, and in the evening
are due almost entirely to cooking activity. Increased hot water use
during these times also contributes to the peaks.
x
-------
One step in the investigation of human activity impact on
indoor air quality is the setting of baselines of human occupancy hours
during which indoor air must be suitably conditioned. This baseline
involves making detailed estimates, for various types of spaces of the
frequency, intensity, and duration of human occupancy which the spaces
experience.
Chapin and Brail [118, 119] devised a 13-class activity
profile of metropolitan activity and mobility patterns. These 13 person-
initiated activities are delineated by the relative freedom with which
a person engages in an activity. There are three categories in the system
devised by these investigators. Firstly, activities are performed either
in the home or outside the home allowing a basic split in environmental
conditions surrounding activity performance. Secondly, the authors dif-
ferentiate between discretionary and obligatory activities. Discretionary
activities are those in which an individual exerts his own initiative
towards the performance of the activity, such as reading, socializing,
or relaxing. Obligatory activities are those sustaining activities
required by human physiology, such as sleeping and eating. The terms
discretionary and obligatory can be viewed as the "polar extremes," with
most activities falling in between, having both discretionary and oblig-
atory aspects. Finally, the 13-class activity profile differentiates
activities by the level of interaction between the performer, other
individuals, and their environment [118, 119].
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Thus three parameters, location of activity performance, dis-
cretionary and obligatory classes, and levels of interaction, define
elements of the following 13-class system:
1. Relaxation
2. Arts, hobbies, and sports
3. Reading
4. Television and radio
5. In-home family
6. In-home socializing
7. In-home obligatory
8. Out-of-home discretionary
9. Out-of-home family
10. Out-of-home socializing
/-
11. Work related
12. Shopping and personal services
13. Out-of-home obligatory.
The first seven are in-home activities, and of these seven, the first six
are classified as discretionary. In-home obligatory activities include
housework; home, yard, or car maintenance; eating meals at home; personal
care chores; child-centered activities; and the like. The last six activ-
ities are performed out-of-home, and the final three are obligatory. Out-
of-home obligatory activities Include household errands, medical care
trips, taxi type driving chores, and eating meals out of the home within
a nonsocializing context. As suggested earlier, the authors' focus has
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been upon the discretionary activities, and their activity classification
scheme has been constructed with this focus in mind. Table 29 contains
the percentages of individuals performing the different activities and
the mean durations of those who do perform the activity at least once
during the day [118].
TABLE 29. PERCENTAGES OF INDIVIDUALS PERFORMING AN ACTIVITY ONE TIME OR
MORE DURING A WEEKDAY AND THE MEAN DURATIONS OF THE ACTIVITY,
FOR METROPOLITAN UNITED STATES [ll8]
Activity Class
Relaxation
Arts, hobbies, and sports
Reading
Television and radio
In-home family
In- home socializing
In- home obligatory
Out-of-home discretionary
Out-of-home family
Out-of-home socializing
Work-related
Shopping and personal services
Out-of-home obligatory
Percentage
48
10
29
66
10
14
100
15
11
13
47
35
49
Mean Duration
(hours)
1.65
2.76
1.34
3.08
1.65
1.81
5.67
*
2.71
2.33*
2.64
A
8.69
1.72*
1.57*
* Includes the full amount of travel time to the activity and from the
activity if trip begins or ends in the home. If travel for the activity
begins or ends in a place other than the home, only half the travel
time for the leg of that trip is included in the time spent at the
activity.
The personal activities of individuals may in themselves be
pollutant-generating - as for example in the use of aerosol - as well as
resulting in exposure by the individual to pollutants.
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6.3 OVERVIEW
Building occupancy has been quantified for various structures
as a percent of total occupancy by time. Information on occupancy of
dwellings and rooms within dwellings and other structures has not been
quantified, although such information can be obtained roughly from
previous attempts at quantifying the amounts of time people use per-
forming a variety of activities. Activity profiles of building occupants
have been investigated, although these are of only moderate use in rela-
tion to activities involving building ventilation or indoor pollutant
generation. It is evident that, if data about human occupancy of indoor
space are to be used in future to determine human exposure to indoor
pollutant concentrations and pollutant dosages, it will be necessary to
obtain data based on a more finely structured grid of space and time
.dimensions within buildings than has been customary in the occupancy
research described in this report.
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Section 7.0
ENERGY CONSERVATION MEASURES IN BUILDINGS
7.1 INTRODUCTION
This section has two purposes. The first is to provide an
appraisal - based upon a review of relevant literature - of the state-
of-the-art technologies available for reduction of energy use in
buildings. The second purpose is to consider - again based upon the
literature - some of the relationships between energy conservation
measures and indoor air quality characteristics of buildings.
In Section 7.2, there is a discussion of various possible
energy conservation modifications categorized into those which do and
those which do not directly affect air change rates in buildings. Where
possible, an attempt has been made to quantify the perturbation of air
change rate of a particular modification.
Subsequently in Section 7.3, there is a discussion of
building climatology and of some of the relationships between indoor air
quality and the operations of heating, ventilating and air conditioning
systems in buildings. A detailed investigation and evaluation of the
effectiveness of commercially available air cleaning devices (for example,
filters and electronic precipitators), and of quantitative relationships
between energy conservation measures and indoor air quality, was not
included in the scope of the first phase assignment which resulted in this
present document. A detailed study of that kind, intended to produce
quantitative information about air cleaning-air quality-energy conservation-
cost relationships in indoor environments, based upon a combination of
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literature search and new field research, will soon begin as a part of
the Phase II EPA-sponsored study of indoor air pollution being per-
formed by GEOMET. Results of that study will become available in late
1977. The discussions of indoor air quality and energy conservation
relationships which appear in Section 7.3 of the present document are
therefore of a preliminary, qualitative nature only.
7.2 ENERGY CONSERVATION MODIFICATIONS
7.2.1 Definition of Characteristic House
Many examples will be given in this section that require examin-
ing a specific residential building. In order to facilitate this, a
characteristic house has been defined. This house is representative
of many residential buildings in the northeastern part of the United
States. It should be noted that an attempt was made to use a somewhat
"average" characteristic house, but that it could not possibly be
representative of all styles of houses in the U.S. Specific results
and conclusions based on an analysis of the characteristic house are
not necessarily directly applicable to other style houses.
The structural and energy consumption parameters which describe
the characteristic house are given in Table 30; the floor plan of the
house is shown in Figure 15.
7.2.2 Structural Modifications
The first group of energy conservation measures which will
be discussed is structural modifications to a building. Some of these
modifications can practicably be considered only in the design stage of
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NORTH
CO
ro
i
SECOND FLOOR
DINING
ROOM
KITCHEN
FAMILY
ROOM
LIVING ROOM
PATIO
o
CAR PORT
UP
BASEMENT
Figure 15. Floor plan of characteristic house.
-------
TABLE 30. DESIGN PARAMETERS FOR CHARACTERISTIC HOUSE
Structural Parameters
Energy Consumption Parameters
00
OJ
Number of Stories
Basement
Garage
Floor Area, ft
Construction Type
Exterior W alls:
Outside Surface
Sheathing
Insulation
Inside Surface
Ceiling Insulation
Attic
Roof
Windows:
Type
Glazing
Area
Exterior Doors:
Type
Number
Total Area, ft2
Patio "Door:
Type
Glazing
Area, ft2
Two
Full (Unfinished)
Attached, Open Carport
1695 Finished
Wood Frame
Wood Shiplap
Plywood, 1/2 inch
R-7 Batting, 1/2 inch
Drywall, 1/2 inch
Loose Fill Blown-in 5 inches
Ventilated, Unheated
Asphalt Shingles
Aluminum Casement
Single
180
Wood Panel
3
60
Aluminum Frame
Single'
40
R7 Equivalent to 2-1/4 inch Fiberglass Batting.
Energy Consuming Equipment:
Heating System
Cooling System
Hot Water Heater
Cooking Range
Clothes Dryer
Refrigerator/Freezer
Lights
Color TV
Furnace Fan
Dishwasher
Clothes Washer
Iron
Coffee Maker
Miscellaneous
Forced Air, Gas
Forced Air, Electric
Gas
Gas (90 therms/year)*
Gas
Electric (1830 Kw-hr/year)*
Electric (2000 Kw-hr/year)*
Electric (500 Kw-hr/year)*
Electric (394 Kw-hr/year) *
Electric (363 Kw-hr/year)*
Electric (103 Kw-hr/year)*
Electric (144 Kw-hr/year)*
Electric (106 Kw-hr/year)*
Electric (1200 Kw-hr/year)*
* Energy Input to Structure Due to Use of Item.
Factors Affecting Heating/Cooling Load: (Base Case)
Exterior Glass Areas
External Landscaping
Dwelling Facing
External Colors
People
Weather
Garage Location
70% Draped
20% Shaded
10% Open
Patio Door on South Wall
No Awnings, No Storm W indows
No Shading Effect
North
White Roof and Walls
Two Adults, Two Children
Data for 1954 from Baltimore, MD.
Weather Station
West Side
-------
a building (such as building orientation, ratio of external wall area/
floor area, and thermal capacity of the structure). Most of the other
modifications can be considered either before or after the building
has been erected. The first part of this section will be devoted to
those structural modifications which have, as their primary effect, an
impact on air infiltration into a building. The second part of this
section will deal with structural modifications which do not directly
affect air infiltration, but conserve energy in some other way.
7.2.2.1 Modifications Which Directly Affect the Air Change Rate
Storm Doors and Windows
Storm windows have been cited by the National Bureau of
Standards as the one insulating component that saves more fuel dollars
than any other component. (This result is based on a test house in
which the NBS engineers monitored different energy saving measures
using infrared photography.) The fuel savings achieved by the addition
of storm windows over typical single-glazed windows are through two
mechanisms:
They reduce infiltration of outdoor air through
the window area by increasing the resistance to
air flow through the cracks between the window
sash and frame.
They create a relatively inactive air space
between the primary window and the storm
window, which adds insulating value to the
window area.
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The addition of storm windows will typically reduce infil-
tration around the window due to wind by about 15 to 30 percent. They
will also reduce the conductive heat loss through the glass area by
about 50 percent. The combined effects of reduced infiltration and
increased insulation resulting from the addition of storm windows can
represent a total savings on fuel for heating and cooling of 10 to 25
percent in typical residential buildings. The exact savings achieved
by any particular installation will depend on the characteristics of the
building, the quality and type of the materials and the workmanship.
The types of storm windows which may be installed:vary widely,
from a plastic sheet taped over the window to a permanently installed
system which allows for opening of the storm sash and sliding a screen
into place over the opening. In any type of storm window, the benefit
gained from it will be affected by the quality of the product and the
workmanship of the installation. If large cracks are left around the
perimeter, the window will be less effective in reducing infiltration.
Storm doors affect infiltration in the same way as storm
windows; that is, they increase resistance to air flow through the cracks
around the door. Storm doors, however, do not reduce the conductive
losses through the door area as effectively as storm windows reduce the
conductive loss through the window area.. Table 31 shows the difference
in conductive loss per square foot of area for windows with and without
storm windows, and for doors, with and without storm doors. Table 31
shows a reduction for conductive losses through the window area of 47
percent due to the addition of storm windows, and a reduction of con-
ductive losses through the door area of 36 percent due to the addition
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of storm doors. The reason that the reduction of conductive losses due
to storm doors is less than for storm windows is that a door is usually
a better insulator than a window. The addition of a small amount of
insulation to a door therefore has less of an effect than the addition
of a small amount of insulation to a window [2, 18, 38, 145, 157, 327,
254, 174, 299, 302, 340, 449, 596, 300, 301, 51, 477, 667, 668].
TABI£ 31. INSULATING EFFECTS DUE TO THE ADDITION OF
STORM DOORS AND STORM WINDOWS
Door Only
Door and Storm Door
Window Only
Window and Storm Window
R-Value
1.77
2.77
0.94
1.79
U-Value
(Btu/Hr.Ft. OF)
0.565
0.361
1.06
0.56
Percent Reduction
of Heat Flow
36%
47%
Caulking and Weatherstripping
Air infiltrates into a building through any opening or crack,
such as those around window and door frames, whenever the pressure out-
side is greater than the pressure inside. The amount of infiltration
is a function of the pressure difference and the size of the crack or
opening. Therefore, filling cracks with caulking and installing weather-
stripping to reduce the crack size around windows and doors will decrease
infiltration.
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Tests have shown that the use of properly Installed weather-
stripping can reduce the infiltration through the cracks between window
sash and frame by as much as 80 percent. To achieve results like this,
the weatherstripping must be reasonably good quality material, it must
be cut accurately to the size of the window, and it must be carefully
installed to insure that no gaps are left when the window is closed.
Caulking any cracks will also reduce air infiltration. The
most common places cracks occur which should be caulked are:
0 Around window and door frames
At corners formed by siding
At the foundation sill
0 Where pipes or wires penetrate the outside
wall or a wall or floor between a heated
and unheated space
0 Where two different materials meet (such
as masonry meeting siding)
Where the ventilators, mail slots, or other
penetrations of the exterior wall occur.
References are [2, 18, 44, 157, 174, 201, 327, 254, 287, 299, 300, 302,
340, 398, 449, 596, 597, 477, 667, 668].
Pointing and Filling
As a brick or stone building ages, the mortar joints deterior-
ate and begin to crumble. The weight of the masonry itself is usually
sufficient to prevent large gaps from forming in the walls, but smaller
gaps may still be formed. Pointing and filling reduces the size of the
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cracks and crevices in a masonry wall, thus reducing the infiltration
through the wall [302].
Decreased Window Area
Air infiltrates into a building through the cracks around the
outside of any window. A reduction in window area would produce a reduc-
tion in the total crack length around windows. However, the crack length
is not reduced by as large a percentage as the window area. Since area
is a function of the square of linear dimensions, a reduction in window
area produces a reduction in crack length approximately equal to the
square root of the reduction in window area. For example, a 4' x 5' win-
2
dow has 20 ft of area and 18 ft of crack around the perimeter. The area
2 2
of the window would be reduced to 80 percent of 20 ft or 16 ft if it
were changed to a 4' x 4' window. But a 4' x 4' window has 16 ft of
crack, about 89 percent of 18 ft or (»CF) x (18) (see Figure 16). This
relation is very close for windows that are approximately square, but
breaks down on windows that are very long and narrow.
Besides reduced infiltration due to fewer linear feet of crack
around a smaller window, such a modification is also accompanied by an
increase in the overall insulating value of gross wall area. Since
solid walls are typically better insulators than windows by nearly an
order of magnitude, any decrease in window area, and replacement of
that area by solid wall, would bring about a net increase in the
insulating value of the gross wall area [18, 44, 201, 239, 299, 300, 302,
340, 363, 596, 477, 498].
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00
£>
5 Ft.
AREA
PERIMETER
4 Ft.
4 Ftr
Window A
20 Sq. Ft
18 Ft
AREA OF B = (0.8) (Area of A)
PERIMETER OF B « (vO) (Perimeter of A)
4 Ft.
Window B
16 Sq. Ft
16 Ft
Figure 16. Window perimeter crack length as a function of area.
-------
Building Orientation and Configuration
The orientation of a building with respect to its environment
can have a large impact on the amount of energy required to maintain com-
fortable conditions inside the building. The two factors in the natural
environment whose impact is affected most by building orientation are sun
and wind. Conditions usually dictate that the ideal orientations with
respect to each of these two factors are different. A detailed analysis
is required for any particular building to determine the optimum orienta-
tion. The optimum orientation is normally a compromise among the ideal
orientations with respect to each factor considered. The magnitude of
the impact of each factor must be examined and tradeoffs made in order to
arrive at an overall ideal orientation.
Orientation with Respect to Sun
The sun affects buildings and their energy use in many ways.
It shines through windows providing light and warmth for the building's
occupants. In the winter months, the heat gained from the sun is welcome,
but in the summer, the additional heat from the sun must be removed by
the building's air conditioning system.
The amount of sunlight which shines in through a window or
impinges on an opaque surface depends upon its orientation. The ideal
orientation with respect to the sun for any particular building is a
unique problem and depends upon the geographic location, building physical
parameters, building use, etc. Generally (in the Northern Hemisphere)
buildings in warm climates should have a minimum of glass on the southern
side; buildings in cold climates should have a minimum of glass on the
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northern side. The longer dimension of a building should lie in a gene-
rally east-west orientation to avoid unnecessarily wide variations of
solar impact on the building during the day.
Orientation with Respect to Wind
The impact of building orientation on winds effects are shown
Figures 17 and 18. Figure 17 is typical of most single-family houses;
Figure 18 is typical of townhouses or low-rise apartment buildings.
As shown in Figure 17, the rotation of a building that has
approximately the same dimensions on each of its four sides by 45° radi-
cally changes the air flow pattern around the building. In Figure 17a
the direction of the wind is normal to one of the surfaces of the build-
ing, creating a very high pressure zone on the windward side of the build-
ing. The resultant effect on the building is infiltration of air through
the wall on. the high pressure side and exfiltration of air through the wall
on the leeward side. In Figure 17b, no surface of the building is normal
to the direction of the wind. The resultant flow of air around the build-
ing is substantially less turbulent and with smaller pressure differences
than in Figure 17a. Because of the smaller pressure differences, air
infiltration is considerably less in Figure 17b than in Figure 17a.
(If windows are fairly evenly distributed on all four walls, Figure 17b
would have about 15 percent less infiltration due to wind than Figure 17a.)
Figure 18 shows the importance of orientation with respect to
prevailing winds of a building which has one dimension much larger than the
other, such as is typical of townhouse or low-rise apartment construction.
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10
ro
17a.
17b.
Figure 17. Air flow around single-family dwelling as a function of orientation with respect to wind direction.
-------
UD
CO
I
18a.
Figure 18. Air flow around townhouse or low-rise apartment building as a function of orientation with respect to wind direction.
-------
In Figure 18a, the building is situated to minimize air infiltration due
to wind. The high pressure zone created at one end of the building and the
low pressure zone at the opposite end cause infiltration in the two end units.
But since a path through the building in the long dimension is blocked by
several party walls, infiltration effects in the interior apartments are
minimized. If the building is oriented as shown in Figure 18b, a high
pressure zone is created all the way across one long dimension of the build-
ing, and a low pressure zone on the outer side. This causes increased
infiltration in all the units in the building [18, 157, 239, 299, 300,
302, 340, 363, 474, 596, 668, 719].
Non-Operable Windows
The infiltration of air through the spaces between an operable
window sash and the frame accounts for about 50 percent of the infiltration
due to wind in the average residence. The infiltration through cracks
around the window frame account for an additional 15 percent. If an operable
window were replaced by a non-operable window, the crack size around the
window would be greatly reduced, though not completely eliminated. This
would reduce the infiltration due to the window but would not affect the
infiltration due to the window frame.
This particular modification would also eliminate the possibility
of using natural ventilation. Mechanical ventilation would be required
year-round. In residential applications, such a modification would have to
be considered as having an impact on the life style of the occupants of the
residence. In addition, the need for year-round mechanical ventilation
would offset some of the energy savings due to reduced infiltration [302].
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Elimination of Fireplace
A fireplace can add to the esthetic value of a room, and when it
is in use, it supplies that room with a considerable amount of heat. But
while a fire is burning, a considerable quantity of air is being drawn into
the house through all the cracks around doors, windows, etc., and drawn
up the chimney. In fact, depending on the size and stage of the fire, a
fireplace can cause over 200 cfm of infiltration, which would approximately
double the infiltration in an average house. This causes all the rooms
other than the one in which the fireplace is located to become quite cool
unless one provides for ventilation air directly to the fireplace. (Open-
ing a window in the room to provide air for the fireplace is a possible
solution, though this causes cold drafts within the room.)
During the course of a typical use of a fireplace in a residence,
including burning of the fire, and allowing for the damper to remain open
until the following morning, it is estimated that approximately 85,000 ft3
of outside air are drawn through the house, or a total of approximately
6-1/2 air changes in an average size (1600 ft2) house. Assuming a 50° F
temperature difference between indoor and outdoor, approximately 1/2 gallon
of oil would be required to heat the air which infiltrated due directly to
the fireplace.
Even when not in use, unless it is provided with an unusually
well-fitted damper, a fireplace is responsible for some infiltration.
Assuming a crack around three sides of the damper of about 1/4 inch, one
could expect an infiltration rate of about 20 to 25 cfm through the chimney
[299, 302, 340, 499, 596].
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Recirculating Kitchen Hood
A kitchen exhaust fan handles an average daily flow of about
14,000 cubic feet of air. This is based on an 80 cfm fan operating about
three hours per day and accounts for one complete air change in a
1600 square foot house. If this air is all exhausted to the outside,
it is causing an equal volume of air to be drawn in from the outside
through the cracks around windows, doors, etc. The modification of a
kitchen hood to a recirculating fan instead of an exhaust fan would
eliminate this flow of air into the house. Let us look more carefully
at the implications of the modification.
In operation during the heating season, an exhaust fan would
be discarding useful heat (the temperature of the exhaust air would be
about 110°F) and drawing in cold air from the outside, imposing an addi-
tional load on the heating system. A recirculating fan would put the
heat and moisture from cooking right back into the house where it assists
the heating system in maintaining comfortable conditions. But during the
cooling season, a recirculating fan would do nothing to remove the heat
and moisture generated in cooking. Instead, the entire load generated
by the stove would have to be removed from the house by the cooling system.
An exhaust fan, however, would remove much of the heat and moisture gene-
rated in cooking, and even.though it would cause additional infiltration
of air, the outside air being drawn into the house would almost always be
cooler that the exhaust air.
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Since it is impractical to install two kitchen fans, one that
recirculates air and one that exhausts the air to the outside, it is
important to choose the right type of fan for a particular installation.
In general, a recirculating fan would be better in cooler climates, and
an exhaust fan would be desirable in warmer climates [254, 299, 302, 340,
667].
Vestibule Doors
The use of vestibule doors in place of single doors affects
energy consumption for heating and cooling in three ways:
1. They reduce air infiltration into the building
by increasing the resistance of air flow
through the cracks around the door.
2. They increase the insulation value of the
door area by the addition of an air space
(the vestibule).
3. They decrease the quantity of outdoor air
entering the building each time the door is
used as an entrance or exit.
By creating a buffer zone between the interior of the building and its
external environment, the use of vestibule doors is more effective in
saving energy than storm doors. The savings achieved by using vestibule
doors instead of single doors are twice as large as the savings achieved
by using storm doors [18, 38, 299, 302, 448].
Automatic Door Closers
Each time a door is opened to allow a person to enter or leave
a building, outside air enters the building, displacing the air that was
.-197-
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previously occupying the space. The volume of air that enters a building
each time a door is opened depends upon the wind speed, the duration for
which the door is open, and any air pressure differences between the
interior and exterior of the building. By reducing the time a door is
open, an automatic door closer decreases the volume of outside air which
enters the building [18, 327, 299].
Outdoor Landscaping
The proper use of trees as windbreaks can reduce air infiltration
into a building. A windbreak temporarily diverts a fraction of the air-
stream upward, creating an area on the leeward side of the windbreak that
has reduced wind speeds. The airstream will return to the level from which
it was diverted, but typically a 50 percent reduction in wind speed will
be experienced as much as 15 barrier heights downwind of the windbreak.
For example, if the barrier were 20 feet high the 50 percent reduction in
wind speed would be present, at most, 300 feet downwind of the barrier.
Since trees let some wind through it is unusual for a windbreak constructed
of trees to cause a reduction of as much as 75 percent in wind speed, but
a large area downwind of the trees will experience a modest reduction in
wind speed. A distance downwind of the windbreak equivalent to almost
30 times the height of the windbreak may experience more than a 25 percent
reduction in wind speed.
Barriers which allow little or no wind to penetrate at the lower
levels provide a short range of very good wind protection (over 75 percent
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reduction in wind speed), but not as extended a range of moderate protec-
tion as provided by a less dense barrier. Also within the area of 75 per-
cent reduction of wind speed, eddies and turbulence can be expected [18,
157, 474, 596].
7.2.2.2 Structural Modifications Which Do Not Directly Affect
Air Change Rate
Insulation of Walls, Roof, and Floors
Insulation is a material that has a high resistence to the flow
of heat. The use of these materials in insulating the walls, roof, and
floor of a building is the most basic energy conservation measure that can
be taken. It is cited as one of the first steps to take in almost every
reference that deals with ways to save energy in buildings. The instal-
lation of an average thickness of insulation or the deletion of insulation
entirely from the walls, roof, and floor of a house can cause a variation
in the energy required for heating and cooling of about 50 percent.
The resistivity of a material to the flow of heat is termed the R-
value of that material. The reciprocal of the R-value is the U-value, which
is a measure of the conductivity of a material. Each of the many materials
used for insulation (e.g., wood, wood fiber products, plastics, brick, glass
fibers and plaster board) come in different forms, such as boards, foams,
blankets, loose particles and masonry. The R-value will be specific for the
material and the form (boards, blankets, etc.) that it is in. The resistence
to the flow of heat by any given material and form is determined by multiply-
ing the resistivity (R) by the thickness of the material.*
* Merkel, J.A. 1971. Basic Engineering Principles, University of Maryland, College Park, Maryland.
-199-
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In the characteristic house defined at the beginning of this
section, the part of the heating load due to losses through the walls,
roof, and floor is about 30 percent of the total heating load. The
walls, roof, and floor also account for about 20 percent of the cooling
load. If the insulation were removed from the roof and walls, the R-
values of those components would change as shown in Table 32.
TABLE 32. COMPARISON OF VALUES WITH AND WITHOUT INSULATION
Wall
Roof
R-Value
With Insulation
10
15
Without Insulation
3
4
U -Value
With Insulation
0.1
0.067
Without Insulation
0.33
0.25
As Table 32 shows, the heat flow through either the walls or
the roof would increase more than three times if the insulation were
removed from the house. The increased heat flow through the walls and
roof would result in an increase of about 50 percent for the energy
needed to heat and cool the house.
Perhaps as important as the insulation itself is the manner in
which it is installed. If insulation is cut short so that it does not
extend the full width, height, or length of the space it was intended to
fill, then heat leaks out around the edges of the insulation. Care must
be taken when installing insulation in attic floors so that ventilation
of the attic is not blocked. (Ventilation is required to remove moisture
which would otherwise condense in the insulating material, lowering its
R-value.) Small spaces around windows and doors must be filled with
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insulation or heat will leak out through those spaces. Vapor barriers must
be installed properly or moisture will condense in the insulation and lower
its efficiency. When insulation is compressed more than it should be, as
is usually done to fit it around pipes, it loses efficiency. Installing
insulation properly is not difficult, but it can greatly improve the per-
formance of any insulating material [2, 18, 44r 70, 145, 157, 327, 201,
239, 254, 174, 287, 299, 301, 302, 340, 363, 448, 449, 453, 474, 499, 518,
596, 598, 666, 668, 667, 719, 51, 477, 498].
Double-Glazed Windows
While windows typically comprise 5 to 8 percent of the total
area of the envelope of a residential building, they account for nearly
30 percent of the conductive losses through the building envelope. A
double-glazed window can reduce the conductive losses through the glass
area by about 50 percent.
Figure 19 shows the components through which heat must flow for
a single- and double-glazed window. Figure 19a shows that for single-
glazed windows, almost all of the thermal resistance is in the air films
on the interior and exterior surfaces of the glass. The double-glazing
(Figure 19b) retains the benefit of the interior and exterior surface air
films, and adds a very significant air space. The extra thickness of glass
has very little effect on the increased R-value of a double-glazed window.
Window manufacturers have achieved U-values even lower than 0.58 by utilizing
special surface treatments on the glass surfaces which face the air space
[18, 44, 327, 201, 174, 301, 302, 340, 363, 448, 449, 668, 667].
-201-
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P\
INSIDE SURFACE FILM-*r
ro
i
A
INSIDE SURFACE FILM
GLASS
A. SINGLE GLAZING
R-Value
OUTSIDE SURFACE FILM
Inside Film
Glass
Outside Film
Total
0.67
0.04
0.17
0.88
1.13
^-OUTSIDE SURFACE FILM
GLASS 1 T GLASS 2
AIR SPACE
B. DOUBLE GLAZING
R-Value
Inside Film 0.67
Glass 1 0.04
A1r Space 0.8
Glass 2 0.04
Outside Film 0.17
Total T77T
u ' if-.1777- °'58
Figure 19. Window component* which contribute to the residence to heat flow.
-------
Operable Insulating Shutters
The heat loss or gain through glass areas can be reduced by 80
to 90 percent (Table 33) when an insulating shutter is in place over the
window. Since the conductive losses through the glass area of residential
buildings typically comprise about 30 percent of the building's conductive
losses, insulating shutters would reduce the conductive loss for the entire
building by about 25 percent while the shutters are closed.
TABIE 33. BENEFITS OF INSULATING SHUTTER
R- Value
Window
Insulation
Total
0.88
5
5.88
1.13 -0.17
1.13 -°'S£
'U -Value
With Shutter =
5.88 =0'17
U-Value
Without Shutter =
0.88 =1'13
> = 85% Reduction in Heat Loss/Gain
Of course, the installation of insulating shutters in a building
does not guarantee an energy saving. The occupants of the building must
be willing to use the shutters, which means that the shutters must be
designed so that they are attractive and easy to use [299, 596, 668,
667].
Increased Thermal Capacity of the Building's Structure
If two buildings were identical except for their thermal capacity,
the building with the larger capacity would use less energy. This effect is
-203-
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most pronounced if the additional thermal capacity is in the envelope of
the building. The greatest impact of this effect is on the cooling load.
When the sun shines on a building wall, it heats the wall. If
the wall has a very small thermal capacity, that heat is seen as a load
on the inside of the building in a very short time. If the wall has a
greater thermal capacity, it can take several hours before the sun's heat
is transferred through the wall to the interior. When the load finally
reaches the building's interior, the peaks have been reduced and distri-
buted over a longer period of time. This allows for smaller size air
conditioning equipment. Besides distributing peak loads over a longer
period of time, a wall with a large thermal capacity may hold the sun's
heat well into the evening. When the temperature outside begins to drop,
some of the heat in the wall will flow back out and never appear as a load
on the air conditioning system. Also, by delaying the time that the load
from the sun is felt inside the building, some of the heat will be removed
by the air conditioning system in the evening, when cooler outdoor temper-
atures allow higher cooling efficiency [18, 239, 299, 448, 474].
Provide Shading for Windows
In an ideal situation, sunlight would be admitted into a building
through the windows at times when the outdoor temperature is low, and pre-
vented from entering the building when outdoor temperatures are high. One
action in achieving this ideal situation is the proper orientation of the
building, discussed earlier in this section. Another action is to provide
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proper shading of a building to control the admission of sunlight through
the windows. Sunlight control can be provided in three ways:
1. Reduce the transmission of sunlight through
the glass.
2. Prevent the sunlight from reaching the window
through the use of shading devices.
3. Use shading devices inside the window.
Reduce Transmission Coefficient of Glass
This modification to a building is not really selective control
of sunlight; it effects a reduction of sunlight admitted into the build-
ing at all times. While this solution may not be applicable to many
locations in the U.S., in warm climates, where cooling is required most
of the year, this is a reasonable solution.
Prevent Sunlight from Reaching the Window
When executed properly, this modification is the most effective
method of controlling sunlight. The two most widely used methods of
preventing sunlight from reaching the window are projections of the build-
ing structure, including roof overhangs and awnings, and planting of trees.
Building projections can be designed to allow sunlight to reach
windows in the winter months, but shade the window during the summer months.
This is due to the fact that the sun is higher in the sky during the summer
than during the winter. By examining the solar angles in any specific
location, it is possible to determine the dimensions a building projection
would have to be to selectively block the sunlight.
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Trees can also provide an effective control of sun. The plant-
ing of deciduous trees near a building would achieve the desired result
of selective admission of sunlight. During the warm seasons, the trees
provide a very effective shading device. In the winter months, once the
leaves have been lost, deciduous trees allow most of the sunlight to pass
through, between their branches, and into the building through its windows.
The most significant drawback to either building projections or
trees as shading devices, is that they operate on a relatively gross scale.
That is, as long as the weather remains cold during the winter and warm
during the summer, these devices remain effective. But in the spring and
fall, wide variations can occur and these shading devices cannot respond
to meet the changing conditions. If, however, sun control is maintained
through the use of an external, operable device, such as an awning or
louvers, then, provided the building occupant is willing to take the time
to adjust such devices, effective control of the sun can be maintained at
all times. Automatic adjustable devices are also available, which allow
the sun to enter the building only when the building requires heating.
Use Shading Devices Inside the Window
The most common devices in this category are blinds and curtains.
Both of these, operated by the occupant of the building, can reduce the
effect of sunlight entering a building. However, because they attempt to
control the sun after it has already entered through the window, they are
less effective than devices that prevent sunlight from reaching the window.
-206-
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Light colored blinds and curtains are more effective than those that are
darker because they reflect more sunlight back to ithe outside [157, 327,
239, 253, 254, 174, 340, 448, 474, 596].
Reduce Internal Loads
In many buildings, the largest component of the cooling load is
due to internal generation of heat. Essentially all electrical energy
that is used in a building is dissipated as heat; and other major appliances,
such as ranges and water heaters, regardless of the form of energy input,
contribute significantly to the internal load. In many cases, the reduction
of internal loads can be accomplished, at least partly, through physical
modifications to the building.
Use Fluorescent Lighting Where Possible
Fluorescent lights use electrical energy approximately three
times as-efficiently as incandescent lights. In residences, fluorescent
lighting is generally limited to use in the kitchen, bathroom and utility
areas, since the light is judged objectionably cool for other spaces
within a house. In schools and other public buildings, fluorescent lighting
can be used in almost all locations.
Automatic Pilot Lights
Pilot .lights in gas appliances use as much as 30 percent of the
energy for some appliances. The replacement of pilot lights with any of
the automatic ignition systems available today would significantly reduce
the internal loads.
-207-
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Proper Ventilation of Heat-Producing Appliances
The relative merits of a recirculating kitchen fan and a vented
kitchen fan have already been discussed. The same types of arguments also
apply to the clothes dryer, another appliance which generates large quantities
of heat when in use.
Install Timers on Light Switches in Infrequently Used Areas
This will prevent the accidental continuous burning of unneces-
sary lights.
Install Only High Efficiency Appliances in Buildings
A refrigerator can be the highest electricity consuming appliance
in a house, but the refrigerator's consumption need not be so high. The
least efficient refrigerators available today use approximately three times
as much electrical energy as the most efficient. The proper selection of
refrigerators, freezers and other major appliances can significantly reduce
the internal loads.
The hot water heater is another appliance which consumes large
amounts of energy and whose inefficiency contributes to internal loads.
Hot water heaters with thicker insulation lose less heat to the house than
those with standard amounts of insulation. Also, the hot water heater
should be sized properly to reduce unnecessary standby reserves. For
example, two people living in a house do not need a 50 gallon hot water
heater. In such a case, more water than those two people can use is being
kept hot, and more heat than necessary is being lost from the1tank into
the house provided that the tank is located in the house. Another
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high-efficiency type of hot water heater is one that is modulating.
That is, it has two burners, one to maintain standby conditions, and
a larger one for recovery when hot water is drawn from the tank. Since
the smaller standby burner would not have to. cycle on and off as much
as the larger burner, the water heater operates more efficiently [18,
327, 201, 190, 254, 174, 340, 668, 698].
Reduce the Ratio of Bui1di ng Envelope/Floor Area
Since heat is lost through the area of the building envelope,
reducing the area of the envelope without decreasing the floor area of a
building would result in a potentially more efficient building. The
achievement of the lowest practical building envelope/floor area ratio
would be a configuration of building spaces in which length, width, and
height of the building are nearly equal.
One negative aspect of this modification is that, for most
residential buildings, it would increase the exterior wall area and
decrease the roof area. In houses, because the thickness of the cavity
of a wall is usually smaller than the thickness in which insulation
can easily be installed in the roof, a net reduction in surface area
can result in a net Increase in heat gain or heat loss [18, 363, 448,
474].
Ventilate Attic Spaces
During the cooling season, the temperature inside an unventilated
attic can build up to 20°F or more above the outdoor temperature. This
elevated attic temperature causes a greater heat gain through the ceiling
-209-
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than would occur if the attic were vented. The ventilation of the attic
should be properly designed to achieve the best results.
If an exhaust fan is to be installed in the
attic, be sure to provide for adequate outside
air supply to the attic. If outside air is not
adequately supplied, the exhaust fan will draw
the cool air from the conditioned space below
the attic, causing additional infiltration into
the building.
The control for an attic vent should not sense
just the temperature in the attic, but also the
outdoor temperature. If the exhaust fan is
designed to turn on when the attic temperature
reaches some predetermined set point, the temper-
ature outside could be even warmer than the tem-
perature in the attic, in which case the fan
would operate continuously until the outdoor tem-
perature dropped, allowing the attic to cool down
below the set point of the thermostat. If the
thermostat is set high enough so that the outside
temperature will rarely exceed the set point, then
a rather significant range in which the fan would
be beneficial would be eliminated. But if the
thermostat senses the attic temperature and the
outdoor temperature and activates the attic exhaust
fan when the attic is several degrees wanner than
the outside temperature, both of the preceding
problems are eliminated.
References are [239, 254, 340, 448, 596, 668, 667].
Building and Roof Color
When the sun shines on a building surface, the absorptivity of
that surface determines how much of the sunlight will be allowed to enter
the mass of the wall or roof and become a potential load on the cooling
system or aid to the heating system. The color of the building surfaces
determines, in part, the absorptivity of those surfaces.
-210-
-------
The determination as to whether building surfaces should be light
or dark in color is not necessarily easy. Generally, the cooler the climate
the darker the building surfaces should be, since the cooling loads are less
important and heating loads are more important. But in most of the U.S.,
both heating and cooling are important and a detailed analysis of solar
effects on a building would be necessary to determine the best absorptivity
for the building surfaces [239, 253, 299, 340].
Lower Ceiling Height
Lowering the height of ceilings in a residential building from
8 feet to 7 feet 6 inches produces a corresponding decrease in the surface
area of the exterior walls of the building. The reduction in exterior
wall area, of course, produces a decrease in the heat gain or loss through
the walls.
Other advantages are also achieved with lower ceiling heights.
The reduced area of walls, interior as well as exterior, reduces the
quantity of materials needed in construction. (In some cases, the savings
on materials is not achieved, but is lost in increased waste). Also, the
lower ceiling height produces a space with a more intimate feeling than
one with a higher ceiling [239, 448, 668].
7.2.3 Modifications to the Heating, Ventilating, and Air Conditioning
(HVAC) System"
This section will consider modifications to the heating, venti-
lating and air conditioning (HVAC) systems of a building which result in
energy savings. The first part of this section will consider HVAC
-211-
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modifications which have a direct effect on the air change rate in a
building. The second part of this section will consider those HVAC
modifications which do not directly affect the air change rate.
7.2.3.1 Modifications Which Directly Affect the Air Change Rate
Flue Damper
When a gas, oil, or other combusting furnace is operating, the
products of combustion must be allowed to go up the chimney. But when a
furnace is not actually burning, the flue does not need to remain open.
In fact, if the flue does remain open, heat will be lost through the chim-
ney. An automatic flue damper would close the flue when the furnace is
not actually firing. Two different types of flue dampers could be used.
1. Motorized Damper. This type of automatic damper,
activated by the same signal that activates the
furnace, would open and close as the furnace '
cycled on and off. A malfunction of this system
could cause gases to leak into a building and
jeopardize the well-being of its occupants.
2. Differential Pressure Damper. This type of
damper is actually opened by the hot combustion
gases. As the gases rise in the chimney, they
build up pressure below the damper, which then
opens to allow the gases to escape. This type
of damper also has the advantage that it would
prevent downdrafts from blowing out the pilot
lights.
References are [299, 596].
-212-
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Use of Outdgor Ai r for Combu s t ion
Furnaces are generally installed to use indoor air for combustion,
then exhaust the air, with products of combustion, up the chimney. The
replacement of the air used for combustion causes infiltration into the
building. This infiltration imposes an additional load on the heating
system. Therefore, if a building uses a combustable fuel furnace any
decrease in the furnace operation will decrease infiltration.
Estimates of the percentage of the entire heating load due to
infiltration caused by a furnace range from 3 to 19 percent, depending on
the characteristics of the building. The most common values would be near
the lower end of this range. The use of outdoor air for combustion would
eliminate this cause of infiltration, resulting in lower energy use. This
could easily be achieved by installing a duct from the outside to the
furnace. A damper would be necessary to prevent a gust of wind from
blowing out the pilot light.
The same results could be obtained by changing the heating
system from a combusting source, such as gas or oil, to a noncombusting
source such as electrical or solar energy [299, 596, 668].
"Economizer" Air Conditioning Cycle
Many types of buildings use enough electrical energy, which
dissipates as heat within the building, that the building needs to be
cooled even though the outside temperature is lower than the indoor
temperature. In such situations, it is advisable to use 100 percent out-
door air for cooling, and exhaust all of the return air, rather than
recirculate part of the return air and mix it with some outside air.
-213-
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One of the aspects of this type of system one must be aware of
is that if the controls for the system sense only dry-bulb temperature,
the use of the outside air can, in some cases, be wasteful of energy,
even if it is cooler than the system's return air. The reason for this
is that moisture may have to be removed from the outside air before it is
circulated in the building. The removal of moisture from the air, of
course, can require a great deal of energy. If the system is controlled
by an enthalpy sensor, which takes into account both the dry-bulb tempera-
ture and the moisture content of both the return air and the outdoor air,
the economizer cycle will be capable of operating only when it is in
fact saving energy.
The range of conditions under which an economizer cycle can
operate may be expanded if the HVAC system is designed so that return
air also picks up internal loads, such as heat given off by lights. In
this type of system, the internal loads are intercepted before they
enter the space as a cooling load. Instead, they increase the temperature
of the return air. Whenever the return air has a higher enthalpy than the
outside air, the use of outside air will save energy, so this arrangement
of mechanical systems allows an economizer cycle to provide savings even
if the outdoor air is slightly wanner than the indoor air [44, 201, 174,
287, 300].
Internal Pressurization
Air infiltrates into a building whenever the pressure outside
is greater than the pressure inside. If a building's ventilation system
pressurizes the building, a higher exterior pressure must be reached
-214-
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before infiltration occurs. In order to pressurize a building, however,
a great deal of mechanical ventilation air is required; thus infiltration
through cracks in the building may be reduced, but the air change rate
will probably be higher for a pressurized building than for a nonpressur-
ized one.
Filtration and Reuse of Ventilation Air
The controlling factor in determining the quantities of fresh
air a space needs is not the physiological need for oxygen, but a comfort
factor - the removal of odors and other contaminants in the air. In trying
to lower energy consumption, the-owners or operators of many buildings have
reduced the amount of fresh air introduced into the building. This usually
results in an increase in odors present in the building unless a good air
filtration system is provided. What is meant by a "good" system is one
that is efficient at removing contaminants from the air.
Determining or defining efficiency can be a complex matter
because of such variables as particle size, shape, and specific gravity,
particle concentration and distribution and air stream velocity. In addi-
tion, the ability of a filter to remove dust may vary with time as the
filter collects and accumulates the particulate matter. For these reasons,
there are several standard test procedures for determining air filter
efficiencies. Each standard results in an efficiency of different defini-
tion and its application must be carefully considered. In general, three
types of tests are employed in determining air filter efficiency.
-215-
-------
300
r'.
u,
.u
*
U
H .
200
X,
o
100
VKNTILATION HATli,
CKM
10 20
WIND SI'KIOI). MJ'II
.-300
-200
Figure 20. Infiltration rates as a function of wind speed and ventilation rate.
-216-
-------
U
EXHAUST
FLOW
INFILTRATION RATE
PKESSUIUZATION
FLOW
= TOTAL FLOW
CRACKAGE'
INFILTRATION
FLOW
-300 -200 -100
EXHAUST HATKS. CFM
»200
4300
PKESSUKIZAT1ON FLOW KATES, CFM
Figure 21. Infiltration rate for a 15 mph wind as a function of ventilation rate.
-217-
-------
1. A simple test definition involves passing a
cloud of particles of known uniform size, type
and concentration through a filter. Measurement
of the resulting concentration on the far side
of the filter can then be used to define the
efficiency. This efficiency gives an indication
of the filter's ability to remove only the defined
particle size and is useful only for special
filtering applications.
2. A similar test, to include an entire size and
type spectrum of particulate matter such as
found in typical atmospheric air samples, involves
passing a standardized dust sample through a filter
and determining the efficiency as a result of the
weight fraction of the dust collected. The term
"arrestance" is often used to describe an efficiency
determined as a result of this procedure.
3. A third general category of filter efficiency
involves the discoloration effect of air before
and after being passed through a filter. This
procedure gives an indication of the filter's
ability to remove the finer particles within an
air sample. This type of testing procedure results
in an efficiency often referred to as a "dust spot"
efficiency.
When comparing filters used for the cleaning of ventilation
or recirculated air for general space conditioning applications, it is
useful to know both "arrestance" and "dust spot" efficiencies. These
two parameters give an overall indication of a filter's ability to remove
atmospheric dust.
Currently, when used in central heating and air conditioning
applications, filters with an ASHRAE Weight Arrestance of 85 percent and
an ASHRAE Atmospheric Dust Spot Efficiency of 25 percent can be normally
expected as being the most efficient utilized. These are typically dry
media, replaceable filters and many times are specified to meet pollen
control requirements. Filters normally found on window air conditioners,
-218-
-------
forced air furnace units, and packaged air conditioned units have sub-
stantially lower specifications, typically a 30 percent to 70 percent
arrestance and dust spot efficiencies from practically zero to 20 percent.
Higher efficiency dry media and electronic air filters are presently
available at arrestances near 100 percent and dust spot efficiencies
approaching 100 percent. Aside from cost considerations, the use of
these high efficiency filters is dependent on two other operating
characteristics: air flow resistance and dust holding capacity.
Dry media filters with higher efficiencies have high air flow
resistances. This presents a constraint on system air handling require-
ments. Electronic filters, however, operate at high efficiencies and
with air flow resistances tolerable for typical air handling systems.
Electronic filters are available for residential HVAC application. These
filters operate at spot efficiencies as high as 95 percent, depending on
air stream velocity. The maintenance of these filters is dependent on
the dust holding capacity. At normal dust-holding capacities, the
electronic air filter unit will require frequent periodic cleaning.
Preliminary indications show that the electronic type air filter
is probably the most preferable type of air cleaning device for high effi-
ciency residential air purification. Recent developments in electronic
air cleaning have led to the availability of this type cleaner for the
values of airflow found in residential buildings. Figure 22 shows per-
formance data for a few of the cleaners currently on the market. Among
the type represented are the dry media type which contains a replaceable
dry media filter for collection, the plate type in which the collection
-219-
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CARRIER SIMM MEDIA-TYPE
CARRIER 3TMP714 PLATE-TYPE
CARRIER 31MP220 PLATE-TYPE
ELECTRO-AIR WW-14-H/Y
ELECTRO-AIR WW-2.0-H/Y
100
90
* 80
o
UJ
3 70
u.
u.
UJ
60
50
0.30
0.25
0.20
0.15
0.10
0.05
0.0
o
Oi
o
=>
v>
«/l
Ul
500
1000
1500
2000
AIRFLOW, CFM
Figure 22. Typical performance data for electronic air cleaners (*at determined by NBS Dust Spot Test) reproduced from
technical option* for effective residential energy conservation measures, Hittman Associates, Inc. 1976.
-------
plates are removed to be cleaned, and the water wash plate type (the
Electro-air unit) in which cleaning is accomplished automatically by the
use of a hot water hook up. NBS Dust Spot Test efficiencies, an indi-
cation of the filter's ability to remove the smallest particulate matter,
range as high as 96 percent. Figure 30 also gives an indication of
expected pressure drop when the filter is installed in various airflow
volumes [201, 174, 299],
7.2.3.2 Modifications Which Do Not Directly Affect the Air
Change Rate
Recovery of Flue Gas Heat
Furnaces typically operate at about 80 percent efficiency or
less. This means that about 20 percent of the heat from the fuel being
burned is wasted (much of it going up the chimney) and not contributing
to the heating of the building. The heat that is lost up the chimney
is in a very high energy state, which makes it relatively easy to recover
through heat exchanger devices. Some of the uses to which flue gas heat
could be applied are:
1. Preheat Makeup Air. One way to reduce energy
consumption in a large building would be to pre-
heat the makeup air with flue gas heat. The use
of heat pipes placed in the flues for this purpose
would achieve the desired result with no additional
energy input. An air to air heat exchanger could
also be used for this purpose.
2. Space Heating. Flue gas heat could be used
as an auxiliary energy source for space heat-
ing using either of the above mentioned tech-
niques, heat pipe, or air to air heat exchanger.
-221-
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3. Preheat Combustion Air. Flue gas heat can be
used to preheat combustion air. By preheating
combustion air, the furnace would operate more
efficiently, but the heat of the flue gases would
not be put to as efficient a use in this purpose
as it would if it were used for either space
heating or preheating of makeup air.
Refer to [18, 174, 201, 327, 190, 299, 300].
Recovery of Heat from Exhaust Air
Several methods are available for the recovery of heat, both
sensible and latent, contained in exhaust air. The most widely used
application of heat from exhaust air is to preheat makeup air. This
can be done through the use of several devices.
1. Thermal Wheel. A thermal wheel-is a device
which extracts heat from one stream of air
and delivers it to another stream. This is
accomplished by the use of a slowly turning
wheel. As a segment of the wheel passes
through the warmer air stream, it absorbs
heat. Then, as the wheel rotates and the
warmed segment passes into the cool air stream,
it gives up its heat to the air. Thermal wheels
can be used to recover both sensible and latent
heat.
2. Run-Around Coil. This system is made up of
finned tube heat exchangers in the warm and
cool air streams (exhaust and make-up), with
the heat exchange tubes connected by piping.
The system is filled with a heat exchange
fluid, normally water and ethylene glycol,
which is circulated by a pump. The fluid
picks up heat from the warm air and delivers
it to the cool air. One of the main advantages
of the system is that it can be used even where
the exhaust and supply air ducts are in widely
separated locations.
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Heat Pipe. As discussed previously, a heat
pipe system can be used in any application
where heat must be moved from a warmer location
to a cooler location. Heat pipes cannot be used
unless the exhaust and make-up ducts are immedi-
ately adjacent to each other.
Air to Air Heat Exchanger. In this type of system,
heat is transferred directly from a warmer air
stream to a cooler one by conduction through a
common duct wall. A convoluted duct wall, provid-
ing a greater heat transfer surface, will make
the system more efficient, but normally, the
efficiency of this type of system is less than
50 percent.
Heat Pump. Using exhaust air as a heat source,
a heat pump would be capable of delivering
temperatures higher than that of the exhaust
air. Additional energy input is required; but
when a heat pump has a source that is near 70°F,
it can deliver about 3 Btu's for every Btu of
electrical energy input.
Refer to [18, 327, 287, 201, 415].
Zone Control of HVAC System
Because different parts of a building are subject to different
conditions and uses, they should be divided into separate zones for
heating and cooling system design and operation, with each zone
Individually controlled. In a large building, heat and heat flow
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In zones near the exterior of the building are affected very signifi-
cantly by outdoor conditions, e.g., temperature, wind, and direct
exposure to sunlight. These considerations do not apply to the Interior
zones of large buildings, where the temperature (and humidity) may
be affected only by the presence of the occupants and their activities,
plus, of course, the action of the HVAC system. If the HVAC control
system is not free to provide appropriate and different responses to
the temperature levels existing 1n different zones, the building will
very likely be an uncomfortable place.
Zone control of lighting 1s also Important. Except 1n
industrial and some commercial applications, gang switching of lights
usually results in a waste of energy. Because large areas must be
Illuminated to allow one person to work, switches should be installed
to provide reasonable zone control of lights. The zones for lighting
should be carefully planned. Areas near windows should be placed
on separate switches since these areas will be able to use dayllghting
much of the time. Other areas should be divided into the smallest
frequently used unit of area which 1s practical. For example, one
switch controlling a room 1s reasonable in residential applications
and in relatively small school rooms. But in larger school rooms, such
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as the cafeteria, auditorium, etc., more than one switch should be
provided for lighting with the room divided Into several lighting
areas. In offices, each office should have a light switch rather
than having many offices controlled by a single switch [18, 44, 201,
254, 174, 596, 667].
Separate Make-up A1r for High Exhaust Rate Areas
Building spaces such as kitchens or shops which require a
high exhaust rate should be provided with a separate make-up air system.
This will reduce the load on.the heating system due to Infiltration
1n the rest of the building and will also provide easier control of
the conditions 1n the high exhaust space. This energy conservation
modification has been used for a long time 1n Industrial applications
for activities such as spray painting, and can be applied to other
building sectors without much difficulty [201, 174].
Humidity Control
A properly humidified space can be kept at cooler temperatures
in the winter and warmer temperatures 1n the summer without a detrimental
effect on the comfort of the building's occupants. Providing humidity
control does require additional energy input, but it 1s more than com-
pensated for by the reduction in energy input associated with the lower
heating and cooling loads due to the modified Indoor temperature
conditions. In addition, building occupants will actually feel more
comfortable, especially in the winter, 1f humidity control is provided
[201, 299, 340]. S
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Equipment Sizing
HVAC equipment works most efficiently when 1t 1s operating
near full capacity. In this condition, the equipment does not have to
cycle on and off as frequently as when the load on the system 1s much
smaller than the capacity. If the HVAC system Installed in a building
is too large, 1t will never operate near Us capacity, so 1t will
cycle on and off frequently, which will lower its operating efficiency
and Increase the wear and tear on the equipment.
In many cases, the application of one or more energy conserva-
tion modifications to a building will result 1n the building's HVAC
system being too large. In some cases, such as with a gas furnace,
the system might be easily modified so that its capacity is reduced.
Other systems are more difficult to modify, and may require replacement
to lower the capacity of the system. Since replacement of the HVAC
system normally entails a rather large capital expenditure, this
modification 1s usually not cost effective unless the system must be
replaced for some other reason [201, 340, 449, 668].
Heat Pumps
A heat pump uses electricity to operate a compressor to extract
heat from a low temperature reservoir and transfer the heat to a high
temperature reservoir. This process usually uses about one-half of the
primary energy requirements of electric resistance heat for favorable operating
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conditions. The performance of the heat pump declines as outside air
temperatures drop below 32°F. There are three reasons for this degradation:
the coefficient of performance (COP) is lower, additional energy require-
ments are needed for defrosting operations, and the change in mechanical
properties induce lower efficiencies.
Theoretical analysis shows that the COP is dependent upon the
temperature differential between the low and high temperature reservoirs,
and that the COP will decrease as the temperature differential increases.
In defrosting operations, the heat pump is operated in the air
conditioning mode. This method is universally used in the industry. A
typical heat pump will perform well with frost covering 65 percent to
70 percent of the outdoor coil; however the defrost cycle does not need
to bfe initiated until the heat pump's performance is decreased. The fol-
lowing three methods are used to initiate a defrost cycle:
1. Differential temperature initiation
2. Time initiation
3. Air differential initiation.
Differential temperature initiation measures the temperature difference
between the outdoor coil and ambient air. Whenever the difference is
large, a defrost cycle is started. The problem associated with this mode
is that the heat pump could defrost with only 20 percent of the outdoor
coil covered with frost and operate many unwanted defrost cycles. Time
initiation will start a defrost cycle after a set time interval. Typical
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time periods are around one hour. This mode will also initiate several
unnecessary defrost cycles. Air differential initiation measures the
pressure drop across the outdoor coil to initiate a defrost cycle. This
method best insures that the outdoor coil is covered with frost and that
the system performance is reduced. Although this is a very expensive
design, it has the potential to conserve more energy than the two previous
modes. Defrost operations consume large amounts of energy, and more effec-
tive methods should be developed for energy conservation. It appears that
if defrost operations are to be operated in the air conditioning mode, the
air differential initiation method is most effective to conserve energy.
The major mechanical problems that affect the performance of a
heat pump are the:
Compressor
Working fluid
Maintenance of controls, filters, exchangers
and coils.
A typical heat pump has a welded hermetic design, which has a
high reliability for air conditioners. However, when used in the heating
mode, the compressor operates under greater stress levels at low (32°F
and below) ambient temperatures. The welded hermetic compressor will
develop temperatures near 275°F in the discharge line. The compressor
oil will decompose and create acids at 350°F. The welded compressor has
poor heat transfer properties, and common practice has been to flood the
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compressor with liquid refrigerant. The quantity has to be carefully
controlled to allow sufficient liquid refrigerant to cool the compressor,
and to avoid large flows that will create lubrication and mechanical
problems. The industry has developed a compressor which will operate
favorably under the low temperature heating conditions of a heat pump.
The new compressor will not develop high temperatures and does not require
the periodic flooding of liquid refrigerant. However, this compressor is
about twice as expensive as the conventional welded hermetic design. Low
maintenance or long-term replacement may justify the added expense.
Reliability of long-term data is needed with the present generation of
heat pumps.
The working fluid in most of the heat pumps is Freon R-22. This
refrigerant performs favorably even though it is not as effective as other
refrigerants in heating. The refrigerant, R-22, needs a greater temperature
difference response to heat than other refrigerants such as R-12 and R-502.
Either of these two refrigerants could improve the heat pump performance in
the low temperature heating mode. In addition, the refrigerant R-502 is
less expensive than R-22. The substitution of a new refrigerant for R-22
may enhance the heat pump perfomance to heat, but other operating problems
remain that reduce the performance capability of the heat pump.
A typical heat pump requires periodic maintenance and inspection.
This will provide for more efficient operation and may enhance the system
reliability. A major cause of heat pump failures is related to excessive
temperature in the compressor. Flooding the compressor with liquid
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refrigerant will lower the temperature. Dirty air filters on the inboard
coil will create high discharge pressures which will create high temperatures
in the compressor and consequently decrease the system reliability. The
implementation of an internal pressure relief valve can reduce compressor
failures. Periodic maintenance is still required to attain high levels of
efficiency and energy conservation.
More efficient components, such as compressor, motor, and fan
represent a low level of improvement to heat pumps. A high level of heat
pump improvement can be attained with an additional compressor unit. The
following cycles represent some of the methods that two compressors may be
used to increase the efficiency of a typical heat pump:
Parallel compression
Cascade operation
Series compression
Two staged.
Parallel compression is a relatively easy method to increase heat pump
capacity. Each compressor can be sized differently, and separately con-
trolled to match the heat pump output to the demand. Cascade cycle uses
two compressors and two different refrigerants, and can increase the heat-
ing capacity. Each compressor operates over half of the temperature range
and at a relatively high level of efficiency. Series compression reduces
the mechanical and operating losses associated with low temperature heat-
ing. The two-stage cycle may also be used to reduce these mechanical and
operating losses.
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The low level of improvement represents the implementation of
more efficient components, while the high level of improvement investigates
the potential energy savings of modifications to the standard refrigeration
cycle. The effects that these improvements have in reducing the energy
requirements for the characteristic structures are presented in Table 34.
TABLE 34. HEAT PUMP IMPROVEMENTS
Heat Pump Input
(Therms)*
SFD**
SFA***
Electricity (Thermal) Into Typical Heat
Pump (SPF=2.0)
Low Level Heat Pump Improvement
(SPF = 2.5)
High Level Heat Pump Improvement
(SPF = 3.0)
329
263
219
209
167
139
* The input are electrical (heat) inputs to heat pumps which are required for the heat pump
to satisfy the heating loads of the characteristic residences:
657 Therms for SFD and 417 Therms for SFA.
** Single-Family Detached Housing.
*** Single-Family Attached Housing.
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Gas-Fired Furnaces
There are five major losses related to the operation of con-
ventional gas-fired furnaces which cause the seasonal efficiency for a
furnace to range from 45 percent to 65 percent:
1. Operating stack loss
2. Jacket loss
3. Cyclic loss
4. Pilot light loss
5. Infiltration loss.*
The operating stack loss is defined as the ratio of the flue
losses during furnace cycles to the energy input of the fuel and is usually
about 25 percent. Problems of condensing water vapor and ensuing acid for-
mation in the flue may exist if the stack loss is reduced. There are two
methods to reduce the operating stack loss, which are (1) more efficient
energy transfer from the fuel to the conditioned air, and (2) the imple-
mentation of a heat recovery device in the flue. The furnace can reduce the
operating stack loss to 20 percent through the designs of more efficient
burners and improved heat exchangers without creating any flue problems.
A heat recovery device can be placed in the flue to transfer some energy
from the flue gases to the conditioned air. The device can lower the oper-
ating stack loss to a range from 13 to 21 percent.
* Infiltration loss is expressed as the increase in infiltrated air, used for furnace combustion air.
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The jacket loss Is no more than about 0.2 percent and the
potential energy savings which may be attained are small.
The cyclic loss, which can be as large as 10 percent, is defined
as the ratio of the energy losses due to start and warm-up operations. The
energy losses are due to the cooling of the heat exchanger and can be
affected by the fan temperature settings. The cyclic losses may be reduced
to about 2 percent by lowering the temperature setting for the fan. The
potential energy savings for the cyclic losses is also dependent upon
the type, capacity, and proper sizing of the furnace to the actual operat-
ing conditions.
The pilot light loss may range from 5 percent to 19 percent and
can be eliminated by the implementation of electric ignition devices. An
electric ignition device ignites the pilot light whenever there is demand
for heat. A sensor prevents gas flow to the main burners unless the pilot
light is burning. The pilot light will only burn during main burner oper-
ation and can reduce the entire pilot light loss.
Conventional furnaces are naturally aspirated and draw the com-
bustion air from the air conditioned space. Infiltration air replaces air
used in combustion and can represent up to 10 percent of the total infil-
tration of the residence. There are two methods of eliminating the infil-
tration loss. The outside air may be directly vented to the furnace for
combustion air or the furnace could be located outside the structure.
Either of these methods eliminate the infiltration loss. A 10 percent
reduction in infiltration reduces the heat load of the characteristic
residences by 22 therms and 14 therms for SFD and SFA units, respectively.
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Other factors affect the seasonal efficiency of a furnace. The
majority of furnaces are not properly sized to meet the peak heating load.
In many installations, the furnace capacity is oversized by a factor of 2.
The application of a properly sized furnace could reduce the annual heating
requirement by up to 10 percent. The energy savings for houses which have
been retrofitted with better thermal insulation may be enhanced by the imple-
mentation of a new properly sized furnace which is based upon the peak heat-
ing load of the retrofitted house. Properly sized furnaces could reduce the
heating energy requirement up to 88 therms and 56 therms for SFD and SFA
residences, respectively.
Innovative gas-fired furnace designs may have the potential to
conserve energy. One manufacturer is currently marketing a furnace that
has a unique burner. The furnace is located exterior to the house and
the exhaust gases are released directly to the environment. The burner
is smaller than conventional units and has improved heat transfer properties.
The potential energy savings are up to about 19 percent in comparison to
conventional naturally aspirated gas furnaces (internal to residence).
Another design is a pulse combustion furnace. From 1956 to 1958, pulse
combustion boilers were manufactured for residential hydronic space heat-
ing systems (experimental tests show that the steady state efficiency
ranges from 95 percent to 98 percent). The pulse combustion boiler can
achieve energy savings from 24 percent to 40 percent in comparison to a
conventional gas furnace in actual installations in similarly constructed
residences.
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The low level of furnace improvement has an improved heat
exchanger and furnace combustion air source external to the residence.
The high level furnace improvement represents a typical furnace with an
improved burner design. The energy savings associated with these improve-
ments are shown in Table 35.
TABLE 35. GAS-FIRED FURNACE IMPROVEMENTS
Furnace
Low Level Furnace Improvement
High Level Furnace Improvement
Furnace Inputs (Therms)*
SFD
709
692
SFA
450
438
* The furnace inputs or gas (heat) inputs to furnaces which are required for the furnace to satisfy
the heating loads of the characteristic residences: 657 Therms for SFD and 417 Therms for SFA.
The furnace improvements resulted in the following energy
requirements reductions:
Percent Reduction in Fuel
SFD SFA
Low level furnace improvement 19% 19%
High level furnace improvement 21% 21%
Oil-Fired Furnaces
The design of conventional oil-fired furnaces is very similar
to the conventional gas-fired furnaces. Many of the technical options for
the gas-fired furnace are applicable to the oil-fired furnace, and the
potential energy savings may also be very similar. The operating condition
of an oil-fired furnace is more critical so that annual maintenance is more
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important to conserve energy. One technical option that may be implemented
for oil-fired furnaces is emulsified fuels. The fuel could be a mixture of
oil and water or a mixture of oil and methanol. The fuel mixture can be
emulsified by (1) mechanical mixing, (2) ultrasonic emulsification or (3)
spray techniques. Current research has developed an ultrasonic cavitation
technique to produce water-in-fuel emulsion immediately before combustion.
There are advantages for its application in residential furnaces. The
excess combustion air could be reduced by 50 percent and have lower parti-
culate emissions. The surface of the heat exchanger had fewer carbon
deposits. The conclusions from contemporary studies indicate that increased
fuel oil furnace efficiency could be attained at significantly reduced air
and fuel flows. These potential energy savings enhance the applications of
emulsified fuels in residential furnaces.
A low level of improvement can be attained by a modified burner
design. A high level of improvement can be attained through use of a fuel
emulsifier unit installed into the oil-fired furnace. These improvements
may reduce the heating requirements, and are presented in Table 36.
TABLE 36. OIL-FIRED FURNACE IMPROVEMENTS
Furnace
Output
Characteristic Furnace Input
Input to Low Level Improved Furnace
Input to High Level Improved Furnace
Heating Requirements (Therms)
SFD
657
939
821
747
SFA
417
596
521
474
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The furnace improvements result in the following energy
savings [299].
Percent Reduction in Heating Requirements
SFD SFA
Low level furnace improvement 13% 13%
High level furnace improvement 20% 20%
Mix-Mode Heating Systems
Heat pump manufacturers are currently offering a heat pump package
to assist a furnace for space heating. The heat pump would supply all the
heating requirements down to its balance temperature (about 40°F). Below
this temperature, the furnace would supply all the heat. Two benefits
result from this mode of operation: (1) the heat pump has very high COP's
at moderate temperature differentials, and (2) the cyclic losses for the
furance would also be reduced. The energy saving potential ranges from
10 percent to 5 percent. The actual energy savings depend upon climate,
as well as other factors [299].
7.2.4 Building Operation Modifications
7.2.4.1 Modifications Which Directly Affect the Air Change Rate
Reduction in Percentage of Outdoor Air Intake
Many HVAC systems operate using an arbitrary percentage of outdoor
air which is much higher than necessary. A reduction in the percentage of
outdoor air intake would lower heating and cooling loads, and help control
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humidity. In some cases, a reduction of outside air Intake would neces-
sitate the addition of an air cleaning device to maintain tolerable levels
of odors 1n the building. (A1r cleaning devices are discussed in the
previous section, Modifications to the HVAC System.) Refer to [327, 201,
190, 174],
Reduction in Ventilation Rate
A reduction 1n the ventilation rate would also bring about a
reduction 1n the amount of outside air brought into a building. The
percentage of outside air would remain the same, but the quantities of
air being handled would be reduced. The reduction in volume of air to
be handled would allow a reduction of fan size, saving operating energy
requirements. Also, by reducing the quantity of outdoor air Introduced
Into the building, the heating and cooling loads would be reduced.
Reduction of ventilation rate 1s not a modification that is universally
applicable. If the ventilation rate is already near Its minimum, a
further reduction would require either an auxiliary odor control
mechanism or an auxiliary heating/cooling mechanism [18, 201, 174,
547, 667].
Night Shutdown of Outdoor A1r Intake Dampers
During the night, and on weekends and holidays, many non-
residential buildings have little or no occupancy. For these periods,
it 1s unnecessary to mechanically Introduce outside air because there
are few odor-producing or oxygen consuming activities. The small needs
for fresh air would certainly be provided by infiltration of outdoor
air into the building. The elimination of mechanical ventilation of
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the building with outside air can significantly reduce the energy
consumption 1n the building for heating and cooling operation modes
[201, 190, 174].
Time Clock Ventilation Control
During hours when a building is unoccupied, or experiences
limited occupancy, ventilation 1s unnecessary. In buildings which
have a regular schedule of activity, the hours of ventilation operation
can easily be controlled by a time clock to coincide with the hours
of use of the building. By shutting down the ventilation system at
night, or other unoccupied times, savings are achieved in two ways:
1. The energy normally required to run the fans would
not be used.
2. The ventilation system shut down would eliminate
mechanically induced infiltration.
References are [201, 174, 547].
Zone Control
If a building's mechanical system is provided with zone control,
1t does not save energy unless the system is used properly. The building
operator must be aware of the different conditions in each zone and the
requirements imposed by the activities which occur in each zone. A school
cafeteria, for example, needs relatively high ventilation and can be set
at a lower temperature than classrooms [18, 44, 201, 254, 174, 596,
666].
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Computer Control
In a large building, It is desirable not only to have each zone
responding individually to the conditions of that zone, but for the HVAC
system as a whole to work in its most efficient manner. Means are now
available to control an entire building's HVAC system through a computer.
Programs to do such things as automatically turn off equipment in a pre-
determined priority order as loads become too large, or respond to out-
door conditions before they begin to affect the interior conditions are
available [201, 190, 287].
7.2.4.2 Modifications Which Do Not Directly Affect the Air
Change RaTe"
Nighttime Temperature Setback
Nighttime temperature setback has been cited as a very easy
and effective method to reduce energy consumption. Utility companies
frequently make statements indicating that a savings of 1 percent of
the heating fuel bill can be saved for each 1°F the thermostat is turned
down at night. Studies have indicated as much as 15 percent savings
of the heating fuel bill for an 8°F nighttime setback. Because of the
response of the building to the temperature setback, the savings realized
in a well-insulated building would be, on a percentage basis, greater
than the savings in an uninsulated building. This is due to the
relatively long time it would take for the temperature in a well
insulated building to fall to the lower thermostat setpoint, and
to the shorter recovery time in the morning to raise the temperature
again. Clock thermostats are available which automatically reduce the
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setpolnt 1n the evening and increase it in the morning so that the
building occupants do not have to constantly adjust the thermostat.
[327, 201, 254, 174, 287, 340, 501, 596, 668, 667, 719],
Regular Maintenance of System
By maintaining the HVAC system, it will operate at its maximum
efficiency. Some of the items that should be on a maintenance checklist
broken down by system type are:
011 Furnace
- Adjust and clean burner unit
- Adjust fuel-to-air ratio for maximum efficiency
- Check for oil leaks
- Check electrical connections, especially on safety devices
- Clean heating elements and surfaces
- Adjust dampers and draft regulator
- Change oil filters
- Change air filter
- Change oil burner nozzle
- Check oil pump
- Clean house thermostat contacts and adjust
Tests for furnace efficiency;
- Draft test to see if heat is being lost up the
chimney or If draft is not enough to properly bum
the oil J , .
- Smoke test to see if the oil is being burned cleanly
and completely
- CO? test to see if fuel 1s being burned completely
- Stack temperature test to see if stack gases are
too hot or not hot enough
Coal Furnace
- Adjust and clean stoker
- Clean burner of all coal, ash and clinkers
- Oil the inside of the coal screw and hopper to prevent
rust
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t Gas Furnace
- Check operation of main gas valve* pressure regulator
and safety control valve
- Adjust primary air supply nozzle for proper combustion
- Clean thermostat contacts for proper operation.
The draft test and stack temperature tests for efficiency are also appli-
cable to a gas furnace [2, 327, 201, 254, 174, 313, 598, 667].
Scheduling of Custodial Operations
One way a great deal of energy can be saved is by scheduling
custodial operations to overlap with normal dally activity. This reduces
the requirements of keeping lights on when very few people are in the
building. If custodial operations cannot be scheduled to overlap the
daily building activities, they should be performed in such a way as to
minimize the number of lights needed at any time [201, 190].
7.2.5 Life Style Factors
7.2.5.1 Modifications Which Directly Affect the Air Change Rate
Indoor "Fresh Air" Habits
The effects of almost any energy conserving feature which can
be installed 1n a building can be negated by the occupants' opening of
windows for fresh air. Even if the windows are closed, Infiltration may
account for nearly half of the heating load, so if the windows are opened
to provide more fresh air, the part of the heating load due to infiltra-
tion will increase enormously [299].
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Use of Kitchen, Laundry and Bathroom Vents
Even if vents are provided, they are ineffective unless properly
used. When an appliance which generates heat and moisture is used, it
should be vented to the outside in the summer, and allowed to dissipate
its heat inside in the winter. The use of a vent to discharge heat in
winter should be avoided [299].
Entry and Exit from Buildings
The length and numbers of time doors are opened, either in entry
and exit or for "fresh air" will have a large effect upon the infiltration
of outdoor air into the indoor environment. Just as open windows can
increase energy consumption during the heating and cooling seasons the
extent of increased infiltration of outdoor air through open doors will
have the same effect.
7.2.5.2 Modifications Which Do Not Directly Affect the Air Change Rate
Indoor Temperature and Humidity Settings
In the 1920's, 70°F was the average indoor design temperature.
Between that period and 1970, the indoor design temperature increased by
about 1°F per 10 years until it reached 75°F in the early 1970's. The
recent energy crisis has caused a drop in the indoor design temperature
to 68-70°F, a temperature range that many people are finding to be com-
fortable and economical. Studies have shown a savings of approximately
3 percent of the heating fuel bill for each degree F the thermostat setting
is lowered.
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The same principles hold true for cooling. The temperature and
humidity controls should be set at the maximum comfortable level to
achieve energy savings [2, 18, 327, 190, 174, 596, 598, 667, 719].
Use of Appliances
The use of heat-generating appliances should be limited during
the cooling months. The reduction of use of appliances such as range
and dishwasher would result in direct energy use reduction and an
Indirect reduction because of reduced loads on the cooling system. When
heat-generating appliances are used during the cooling season, an exhaust
fan should also be used [299].
Lighting Levels
Most buildings are over-illuminated. This demonstrated by
the number of buildings 1n which lights were recently removed to reduce
energy consumption. The requirements for lighting for particular tasks
1s usually given in design books as a range of values. Until a few
years ago, most designs used the upper limit of the design range. Today,
more designers are using values that are lower 1n the range for a par-
ticular task [18, 327, 190, 174, 547, 254, 698].
Turning Off Unneeded Lights
When activity is not occurring 1n a space, 1t 1s usually
%
advantageous to turn out lights. This is almost always true for spaces
lighted with Incandescent bulbs, and it 1s true for spaces with fluorescent
lighting if the duration for which the lights will remain off 1s longer
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than about 30 minutes. If the duration 1s shorter than 30 minutes for
fluorescent lights, the cost for replacing the tubes due to shorter life
starts to approach the energy savings.
One of the places turning off lights can be very effective is
1n schools. When one class leaves a room, the lights are usually left
on for the next class, but sometimes the next class will not use the
room for several hours [18, 327, 190, 174, 668, 697].
Use of Operable Shading Devices
If awnings, blinds, curtains, or other operable shading devices
are available for a building occupant to use, the occupant should learn
how to use the device and then use it. By using operable shading devices,
direct sunlight can be excluded from the building when it is not desired,
and admitted when it would be beneficial [299].
Use of Operable Insulating Shutters
If a building has insulating shutters installed on its windows,
their use by the building's occupant can greatly reduce the energy
required to heat or cool the building. In residences, for example,
shutters could be closed at night instead of curtains, and the modifica-
tion of life style would be minimal. Of course, the shutters should be
designed to be easily operated for safety [299].
7.3 BUILDING CLIMATOLOGY AND RELATIONSHIPS BETWEEN INDOOR AIR QUALITY
AND HVAC SYSTEMS
Indoor air pollution behavior has been shown in earlier sections
of this report to be related to the indoor-outdoor air exchange rate of
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a building. Subsequently, in Section 9.0, Modeling of Indoor Air
Pollution Behavior, this relationship will be discussed in detail.
Energy conservation modifications which affect air exchange rates will
also affect the behavior of indoor air pollution concentrations.
Further, many energy conservation measures are implemented through the
operation of the building heating, ventilation and air conditioning
(HVAC) system, which may contain filters and other devices for cleaning
polluted air. The performance of these cleaning systems may be altered
by adjustments of air flow for energy conservation purposes, thus impacting
upon Indoor air quality. One aspect of this, the filtration and reuse
of ventilation air, has already been described in Section 7.2.3, with
a discussion of the measurement of efficiency of filters for particulate
removal. A further discussion appears in later pages in Section 7.3.2.
But before continuing with the relationships between energy conservation
and air quality, it is appropriate to review briefly the influences
of temperature and humidity (whether controlled by an HVAC system or
uncontrolled) upon indoor air quality. This is the subject of the next
section.
7.3.1 Building Climatology
Building climatology may be defined as the regime of temperature,
humidity, and air movement which prevails within the building. It may
vary within the building from zone to zone. Building climatology is
affected by outdoor ambient meteorology (temperature, humidity, wind
speed and direction, Insolation), building structural characteristics,
building use and occupancy and the design and functioning of the HVAC
system.
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The Indoor climatology 1n turn affects the behavior and impact
of airborne pollutants within the building. Temperature gradients within
the building, and between the indoor and outdoor environments, affect
the flow of air in the building and hence the flow and dispersion of air
pollutants.
The ASHRAE Handbook of Fundamentals [22] provides an empirical
relationship which indicates how the indoor temperature affects the
air flow through the buildings:
Q - 9.4 A /h (tQ-t^
where
Q is the air flow rate
A is the free area of inlets or outlets
h is the height from inlets to outlets
ti is the average temperature of indoor air between the
elevations of the inlets and outlets
. tQ is the temperature of outdoor air.
This flow of air in a building resulting from the indoor-outdoor
temperature difference, as described here, is referred to as the stack
effect in ventilation studies [22].
The flow of air occurring in the "stack effect" is derived from
infiltration, the entry of air into a structure from outdoors. The dif-
ference between indoor and outdoor temperature, a climatological parameter,
affects the infiltration rate and consequently the indoor air pollution
-247-
-------
levels. Figure 23 reproduced below provides experimental data that illus-
trate the relationship between air infiltration and the temperature differ-
ence between the ambient temperature and the indoor temperature.
Nov. 30,1973
00 01 02
22
Figure 23. Experimental data illustrating the influence of the building climatology on the
air infiltration [275 ].
Indoor temperature and relative humidity both influence the
chemical reaction rates and the rates of decay of concentrations of
Indoor pollutants. The pollutants which have received the greatest
amount of attention in their indoor chemical behavior are the photo-
chemical oxidants and SOp. Much of the research has taken place in
laboratory environments, in well regulated chambers. Mueller et al.
[439] performed a series of experiments to determine the ozone decomposi-
tion rate for various indoor spaces. Their findings'on the decay constants
-248-
-------
and the half-life of ozone as a function of temperature and relative
humidity in an aluminum chamber and in various enclosed areas are
illustrated below in Tables 37 and 38:
TABLE 37. EFFECT OF RELATIVE HUMIDITY ON OZONE DECOMPOSITION
IN ALUMINUM CHAMBER [ 439]
Volume of Chamber = 76.6 ft3
R.h.
(%)
5
28
48
55
66
87
87
Temperature
(OF)
72.2
78.8-
80.0
80.0
79.2
79.2
79.2
First -Order
Decay Constant
(min'1)
0.0014
0. 0015
0.0029
0.0034
0.0060
0. 0574
0. 0541
Half-Life
(min)
495
462
239
204
115
12.1
12.8
TABLE 38. SUMMARY OF RATE CONSTANTS OBTAINED IN VARIOUS
ENCLOSED AREAS [439]
Flow Rate = 280-300 cfm
Temperature = 70-80 °F
R. h. = 26-50 Percent
Test Area
Decay of ozone in room without carbon filter
Aluminum room. 420 ft
3
Stainless steel room, 525 ft
Bedroom, 1440 ft3
Office, 1950ft
Decay rate with activated carbon filter in
air cleaner
Aluminum room, 420 ft
Stainless steel room, 525 ft
Bedroom, 1440ft3
Office, 1950ft3
First-Order
Decay Constant
(min"1)*
0.054 + 0.004
0. 025 i 0.002
0.121 + 0.004
0.063 + 0.002
0.465 + 0.010
0.323 + 0.016
0.225 + 0.018
0.108 + 0.008
Half-Life
(min)
13
28
5.7
11
1.5
2.1
3.1
6.4
Rate constant with 95 percent condifence limits.
-249-
-------
The Mueller et al. [439] study monitored the decomposition rate of
ozone In several metal test facilities in an office and a home. The
following statements are quoted from the discussion summarizing the
findings of this work.
"The decomposition of ozone was found to follow first-
order kinetics in an aluminum chamber, an aluminum
room, a stainless steel room, an office, and a bedroom.
"The rate of ozone decay was dramatically altered by
variations In humidity or temperature. Increasing
either the humidity level or the temperature enhanced
the rate of ozone decay.
t "The rate of decomposition in an aluminum chamber and
stainless steel room decreased with continuous exposure
to ozone. The metal surfaces appeared to become seasoned
toward this oxidant.
"The half-life of ozone in a typical bedroom was rather
short (6 minutes) suggesting that this pollutant decom-
poses rapidly after it enters typical living spaces.
t "Activated carbon was shown to be effective in removing
ozone from a flowing airstream. The carbon filter
increased the rate of decay and lowered steady-state
ozone levels in a closed room when placed directly down-
stream from an electrostatic precipitator."
A unit commonly used for first-order decay contents is the volume per unit
area per unit time (ft3/ft -min); in this unit the rate constants for
the ozone decay, taken from the table are: aluminum room, 0.054;
stainless steel room, 0.031; office, 0.073; bedroom, 0.122. Given the
difficulties Involved in measuring the true surface areas in living
spaces the last two decay constants should be considered as upper limits
of the quantity.
-250-
-------
A study by Cox and Penkett [144] investigates the "Effect of
Relative Humidity on the Disappearance of Ozone and Sulfur Dioxide in
Contained Systems." If the absorption of the pollutant by the room's
walls is irreversible, which is assumed to be the case, then the best
method of estimating relative values is in terms of deposition velocities.
This quantity is defined as follows:
V =
Total deposition per unit area
g Time integral of volumetric concentration
While V is independent of the surface to volume ratio, it does depend
on fluid flow considerations. V is connected to the decay constant, k,
by the relationship: V = k/r, where r is the surface to volume ratio.
For a first order process the half-life is related to the decay constant
by t-j/2 = 0.693 k. The Cox, Penkett study [144] presents values for
t,,2» k, and V for ozone and sulfur dioxide in two separate containers
as a function of the relative humidity. The "disappearance" of ozone
and sulfur dioxide followed a first-order decay. The straight lines in
the semi logarithmic plots of concentration versus time, in Figure 24
below indicate the irreversible nature of the chemical reactions.
1.0 >f
0.5
0.1
03 on A luminum
78% R.H.
SO2 on Gloss Paint
78% R.'H.
10 20 30
Figure 24. Typical decay curves for sulfur dioxide and ozone [ 144 ]
-251-
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TABIE 39. VALUES FOR k, t^2> AND vg AT VARIOUS RELATIVE HUMDITIES [ 144 ]
SO; on Clo» Paint
R.H.
(*)
30
60
68
78
86
tl/2
(min)
163
31'S
6*8
6' 3
4-8
k
(mm )
4*I3xlO-3
2'20x 10"2
0' 97X10'1
1-05 x 10'1
l'39x 10"1
V.
! 18 x 10-3
6'12x 10- 3
2'69xW2
2'92xlO*2
3'86xlO-2
SO. on Aluminum
R.H.
(«)
11
81
78
*l/2
(min)
4' 2
k
(min l)
l'60x 10"1
V_
(cm i )
1-2x10-5*
3'SxlO-2*
4-45 x W2
Ox me on Aluminum
R.H.
(*>
32
54
76
83
£1/2
(min)
182
155
80
62
J.81 x 10'3
4-46x 10- J
8'67x 10°
l'12x 10-*
6'98x 10"4
8'19x 10"4
T 59x10 "I
2*06 x 10"
Dttt obtiined by Sp.dding (1969).
A detailed review of the photochemical aspects of air pollution
by Altshuller and Bufal1n1 published 1n 1971 [8] Includes a series of
studies that report on the relative humidity effects on a number of
photochemical processes. An example from this study which Illustrates
both the Importance of relative humidity in photochemical reactions and
the difficulty Involved In quantifying Its effects 1s shown 1n the table
of reactivity levels below, from Dimitriades [8], which suggests that
NO oxidation is very sensitive to changes in relative humidity. In a
subsequent study, Dimitriades [8] presents data which show no
systematic humidity effect; he notes that there are many other factors that
must be considered.
TABLE 40. REACTIVITY LEVELS FROM IRRADIATION OF 1.63 ppm C ETHYLENE -5- 0. SO ppm NO
IN THE PRESENCE OF VARIOUS WATER-VAPOR LEVELS
HjO
(mm. Hg)
O.S
3.9
7.2
11.8
Relative Humidity
at Room
T empeiatnre
(77°F)
(*)
2.0
16.4
30.2
49.6
Relative Humidity
at Chamber
Temperature
(93°F)
<*)
l.S
11.7
21.6
35. 4
Reactivity Level
R
NOz
(ppn/nln)
0.00193
0.00265
0.00351
0.00482
Oxidant
(ppm x min)
23.7
28.9
42.4
48.6
HCHO
(ppm x min)
123.9
121.9
145.4
171.7
Maximum
Oxidant
Level
(ppm)
0.23
0.27
0.28
0.27
Maximum
Oxidant
Fotmation
Rate
(ppm/min)
0.0014
0.0017
0.0025
0.0022
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The relations between the building climatological parameters and
the chemical behavior of the indoor pollutants are best studied in
laboratory chambers. The advantage of utilizing such an experimental
technique is related to the complete control of the chamber's temperature,
relative humidity and other environmental factors. It is however very
difficult to extrapolate chamber data to real conditions in buildings.
It is apparent that energy conservation measures which change
the temperature levels or humidity levels in buildings will also have
some effect upon the chemical reactivity and decay rates of reactive
indoor air pollutants such as oxidants and S02. It is not clear, on the
basis of identified research, what the resulting impacts will be in a
complex building environment.
7.3.2 Energy Conservation and Indoor Air Quality
As suggested in the previous paragraph, the search for published
material on the effects of energy conservation measures on indoor air
quality produced very little. What was found indicated that the primary
effect of energy conservation on indoor air quality is due to a decrease
in ventilation and infiltration rates in buildings rather than to indoor
climatological changes. Such measures, while reducing the effect of
outdoor sources of pollution, increase the effect of indoor-generated
pollutants. The increase in concentration of most indoor-generated air
pollutants as a result of decrease in ventilation and infiltration-
exfiltration would be difficult to estimate because the emission rates
of the pollutants are very poorly understood. However, one study indicated
that approximate increases in level of indoor-generated particulates, due
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3.5%
45%
45%
4%
82%
82%
mostly to smoking, could be expected to occur as follows as air exchange
rates are reduced [44].
Average Reduction of Approx. Increase and Con-
Type of Building Ventilation and Filtration centrations of Particulates
Single-family residence
Multi-family residence
Schools
The same study, by Arthur D. Little [44] presents a concise
description of the techniques by which indoor air pollutants may be removed
through HVAC system operations. The authors state that coarse particulates
(larger than 2 urn diameter) can be removed by sedimentation, electrostatic
precipltators, filters, and aqueous sprays. Fine particulates (smaller
than 2 ym diameter) pass through many types of air cleaning equipment
and settle very slowly in air. Citing earlier work the authors note that
reactive gases, such as sulfur dioxide and ozone, can be removed by
reaction with furnishings, structure, aqueous sprays, and adsorbent
filters [65, 439, 534]. Less reactive gases, such as carbon monoxide
and hydrocarbons, are more difficult to remove.
Major air cleaning techniques described by Arthur D. Little
as being applicable for use with HVAC systems (and hence subject to
adjustment of operating modes in energy conservation modifications of
HVAC systems) were:
Filtration. Filters range from the common low efficiency
hot air furnace filter to the high efficiency particulate
air filter.
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Electrostatic Precipitation. Electrostatic precipitators
for participates generally have high efficiencies and low
air resistances. They can generate small quantities of ozone.
Air Washers. These are generally of the spray type or packed
cell type. They can remove participates and S0«.
Gas Sorbents. Activated carbon has been used to remove odors
and ozone and is used in electrostatic room air cleaners to
remove ozone. They can remove SOp.
A discussion of the role played by filters (or other air cleaning
devices) in the mathematical modeling of indoor-outdoor air pollution con-
centrations appears in Section 9.0 of this report. Through mathematical
modeling it should be possible, at least theoretically, to relate a
reduction in ventilation-infiltration-exfiltration rates, planned for
energy conservation purposes, to changes in (1) the chemical decay rates
of reactive pollutants, as a result of changes in indoor temperature and
humidity, (2) the dilution, dispersion and physical removal of indoor
pollutant concentrations, as a result of changed air flow patterns within
the building and through its indoor-outdoor perimeter and (3) the rates
of pollutant removal in filters, precipitators, air washers and sorbents
in the HVAC system, as a result of changed rates of air flow through the
HVAC system ducts.
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Section 8.0
HEALTH EFFECTS
The concern for human health is the principal reason for research
in indoor air pollution. It has been shown that air pollutants occur in
indoor environments at concentration levels which differ from the outdoor,
ambient concentrations of the same pollutants. The indoor concentrations
may be either higher or lower than the outdoor. An initial health effects
research question is: To what extent is the existence of this indoor air
pollution a hazard to human health? A subsequent question, dependent upon
results of the first, is: What actions can be taken to mitigate the hazard?
Research addressing the first of these questions is the subject of the pres-
ent chapter, Section 8.0. The second question is not frentally addressed,
although an approach toward it through modeling is discussed in Section 9.0.
Sections 3.0 and 4.0 have identified work of various investigators
in measuring indoor air pollution concentrations. The measurements have
typically been for short-term durations, ranging from instantaneous peaks
to 1-hour and 24-hour averages. Health impact is a function of human
exposure to pollution. Exposure may be defined as the product of air pol-
lutant concentration and the time in which an individual is exposed to the
concentration. The health effects associated with exposure may vary with
the intensity and with the duration of the exposure, as will be brought out
in subsequent discussions. Studies of the nature and duration of human
occupancy of indoor spaces, an essential element in determining exposure,
have been reported in Section 6.0. Relevant research data are limited in
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-------
extent. As will appear, the existing observational data on short-term
Indoor concentrations of a limited number of air pollutants, and probable
resulting exposures, are inadequate as a basis for definitive conclusions
about the magnitude of the health problems which may exist as a result of
indoor air pollution. But comparisons of the limited, available indoor
air quality data with results of research into the health effects of ambi-
ent pollutants, and with research into health effects of air pollution in
some industrial workplace contexts, will confirm that indoor air pollution
in nonworkplace environments does reach levels at which human exposures
resulting in adverse health impacts may occur. The evidence for this, as
reported in the scientific literature, is discussed in what follows.
The scope of the health effects section of this report was
defined at its outset as a comprehensive review of the state-of-the-art,
described 1n published literature and unpublished ongoing research, of
knowledge of the health effects of those indoor air pollutants for which
studies of indoor concentrations and behavior have been made. Subgroups
of populations which have demonstrated increased sensitivity to those pol-
lutants, and evidence for additive, synergistic or antagonistic properties
of the pollutants with respect to health status, were to be described.
The extent of available information was to be evaluated, and areas of
current research and research gaps identified. Findings from the review
were to be incorporated into an overall appraisal of the potential impact
of indoor air pollution, with a relative ranking of the hazards from
different indoor air pollutants.
-257-
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To address these questions a review and discussion are presented
under the following headings:
t Sulfur oxides
Carbon monoxide
Carbon dioxide
t Nitrogen oxides
Photochemical oxidants
Organic pollutants
Particulates
t Air pollution and lung cancer
r
Susceptibility of population subgroups
Interactive pollutant effects
a Evaluation of indoor air pollutant health hazards
and research priorities.
These headings and the defined scope of the review are ambitious.
The literature of health effects of ambient air pollutants, and of the
related toxicology of industrial air pollutants, is extremely large. Work-
ing within the resource constraints of the overall appraisal of the status
of indoor air pollution represented by this report, the review and documen-
tation of health effects literature have proven to be selective rather than
comprehensive. The hazard ranking of pollutants is a stubborn problem; it
is approached but not resolved here.
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8.1 SULFUR OXIDES
The principal sulfur oxide of interest in health effects studies
has been sulfur dioxide ($02) but sulfate ion (S04), occurring as a com-
ponent of sulfuric acid or its salts (sulfates), has also been extensively
studied. Sulfur dioxide may be converted to sulfate ion (among other
reactions) in chemical transformations which can take place in ambient air
or on surfaces with which S02 comes in contact.
Researchers have found concentrations of SO? measured in indoor
environments to be as high as 182 micrograms per cubic meter (pg/m3) for
a seasonal average [714] and over 1300 vg/m3 for shorter periods [680] to
cite only two values illustrated. Other values have been cited in
Section 3.0. There is sufficient evidence to indicate the existence of an
indoor S02 health effects problem, as the discussion which follows will
show.
The considerable body of research reviewed as background for
setting a National Ambient Air Quality Standard for S02 linked ambient
concentrations with human effects ranging from reduced respiratory func-
tion to increased mortality from a variety of causes [607]. Research
used as reference data in defining the S02 standards is summarized in
Figure 25, taken from Stern et al. [607]. In Figure 25, the vertical
scale at the left shows levels of ambient S02 concentration, over annual
or 24-hour exposure periods, with which the corresponding health effects
were associated. Because the adverse effects demonstrated in these studies
t
were considered to represent the possible combined effects of sulfur oxides
and particulate matter, Figure 25 also shows parenthetically the corresponding
-259-
-------
2000
1000
800
600
500
400
300
200
100
80
60
(6 Cons, 24 hr) increased mortality
(Smoke 750 Mg/m*. 24 hr) increased daily deaths, illneas
(Smoke 300 ug/ra , 24 hr) accentuation symptoms, lung disease
- (Low parttculales, 24 hr) Increased mortality
Standard (24 hr) 365 jig/m3
-------
levels of smoke, coefficient of haze (Coh) or particulates measured in
these studies. The studies reviewed in the preparation of the NAAQS
criteria for SC>2 clearly indicated the hazard of both peak and long-
term exposures to S02 when it is accompanied by elevated concentra-
tions of particulate matter. However, the role of S02 alone in causing
adverse effects at the NAAQS standard levels was not established.
The thresholds for irritant effects of S02 and sulfuric acid have
been reported as 1600-2600 yg/m3 and 600-850 yg/m3, respectively by Bushtueva
[642], Administration-of the two agents together produced these changes at
a substantially lower threshold and Bushtueva considered the effects of the
combination to be additive. Other studies reviewed by NAPCA [642] indicated
that measurable respiratory function changes occurred at levels over 3000 yg/
3 3
m (1.2 ppm) for S02 and over 350 yg/m for sulfuric acid mist, with
associated exposure times of 30 minutes and 15 minutes, respectively.
NAPCA considered that several important toxicological findings were
derived from their review:
Sulfuric acid aerosol is a considerably more
potent irritant than S02, with effects more
pronounced at particle sizes of 3 y MMD or less
and particle sizes less than 1 y MMD were more
effective at lower doses.
Sulfuric acid mist is considerably more irritative
than dry sulfate particles, indicating a more
pronounced effect under conditions of high humidity.
While S02 is absorbed in the upper respiratory
passages and significant protection is provided
by nose-breathing, 80 percent or more (by weight)
of ambient suspended sulfates may be less than
2 y MMD in diameter and penetrate deeply into the
respiratory system.
-261-
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S02 inhibits respiratory clearance through reduced
ciliary action and mucus removal, but at very high
concentrations.
t The effects of sulfur oxides are, for the most part,
related to irritation of the respiratory system.
The apparent minimal effects of S02 at usual ambient levels, the potency
of sulfates and sulfuric acid, and the interaction of S02 and particulates
relate to a number of unresolved issues.
In many epidemiological studies where SOg has shown significant
association with health effects, correlations with particulate concentra-
tions (variously measured as particulates, smoke or soiling) have been
found. A number of investigations have reported a direct association
between the concentration of suspended sulfates and the health effects
[261, 597, 702, 721, 722, 723].
Studies by Sprey and Takacs [597] are interesting in that while
there is no evidence of an increase in the incidence of carcinoma asso-
ciated with exposure to concentrations of S02 alone, there was an increase
in mortality from cancer of various types (respiratory, gastrointestinal,
urologic) when elevated S02 concentrations were associated with elevated
sulfate levels. Winklestein and Gay [699] found a graded positive asso-
ciation between suspended particulates and cirrhosis of the liver. Some
correlation of S02 with mortality from respiratory and cardiovascular
disease was present but strongest associations were found when elevated
particulate or soiling levels were also present. The Sprey and Takacs
[612] data revealed a positive correlation between mortality from arterio-
sclerotic heart disease, and neoplasms of the respiratory and gastrointes-
tinal tracts, with increased sulfate levels. Winklestein et al. [702]
-262-
-------
using sulfur oxides as the pollution measure, found a positive association
between sulfation and chronic respiratory disease mortality.
While results of these studies were not consistent among age,
sex, and socioeconomic groups, and other factors could have been involved
(smoking habits were not measured), presumptive evidence is offered on
several points:
1. Sulfates are involved in disease production beyond
the cardio-pulmonary system, perhaps by reaction
of S02 with metals or other particulates.
2. Although respiratory system cancer was found, pri-
mary bronchiogenic cancer was .not. This may be due
to the high solubility of the sulfates, and their rapid
clearance to the blood, lymph, and gastrointestinal
compartments. This is consistent with findings of
the: prominent effects of sulfur oxides occurring in
the higher respiratory passages.
3. While S02 may serve as a proxy measure, direct
sulfate measurement seems a more appropriate
indicator of the potential hazard involved.
Early studies by Schimmel and Greenburg [545] and Buechley et
al. [96] demonstrated an increased daily mortality in the New York metro-
politan region with higher than usual S02 levels. However, Schimmel and
Greenburg concluded that 80 percent of the excess was attributable to
smoke and only 20 percent to S02. In a recent revaluation of their data,
Schimmel and Murawski [544] and Buechley [97] reached the conclusion that
S02 was a proxy for some other factor. Schimmel and Murawski indicate
the data suggest "that S02 is not only serving as an indicator of air
quality but also that S02 is not an injurious pollutant, at least at the
-263-
-------
ambient levels encountered in New York City in the 1960's - namely,
average levels of 0.2 ppm (525 yg/m3) and peak levels of 0.6 ppm (1575
ug/m3)" [544].'
Finklea and his colleagues analyzed data from CHESS and pre-
sented evidence that adverse respiratory effects in the human are asso-
ciated with sulfates, independent of S02 and other suspended particulates,
In the case of asthma attacks, response to sulfate levels varied with
temperature - the attack rate substantially increasing at lower sulfate
levels when the temperature was above 50°F. For the series of responses
analyzed in these studies, "best judgment" estimates of combined pollu-
tant thresholds were made for adverse effects of long- and short-term
exposures. These are included in Table 41. The authors consider that
suspended sulfates have been identified as a pollutant of present concern
but that there are many unresolved issues pertinent to establishing
standards and control measures. These include better understanding of
the environmental reactions and chemical makeup of sulfates and the bio-
logical response to sulfates.
X
In addition to the potentiating effect of S02 in air that also
contains significant concentrations of particulates (sulfates, nitrates,
heavy metals, etc.) there is evidence that other factors, such as the
relative humidity, have an influence on the functional effects of S02
[150]. Guinea pigs were exposed to 1 ppm of sulfur dioxide and 1 yg/m3
of sodium chloride aerosol. At low humidity .(< 40 percent), the aerosol
was a crystal and at high humidity (> 80 percent), a droplet. Increased
flow resistance and decreased pulmonary compliance were only noted at
high relative humidity.
-264-
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TABLE 41. BEST JUDGMENT ESTIMATES OF POLLUTANT THRESHOLDS FOR SULFUR OXIDES
AND SUSPENDED PARTICULATES
Long -Term Effects (Annual Average, ug/m3)
Increased prevalence of chronic bronchitis
hi adults
Increased lower respiratory disease in
children
Increased frequency of acute respiratory
disease in families
Decreased lung function of children
Short-Term Effects (24-Hour, /Kg/m3)
Aggravation of cardiopulmonary
symptoms in elderly
Aggravation of asthma
so2
95
95
106
200
> 365
180-250
Total
Suspended
P articulates
100
102
151
100
80-100
70
Suspended
Sulfates
15
15
15
13
8-10
8-10
It is postulated that the highly soluble S02 was adsorbed into
the droplets prior to inhalation, with the secondary formation of sulfurous
acid and a lowering of the pH. It is not clear whether the described
changes in respiratory mechanics were related to: the acidity; the (HS03);
the sulfite ion (SOp; or to transport of SQ2 to lower airways by the
aerosol.
It is of interest at this point to note that the Threshold Limit
Value (TLV) established for S02 by the American Conference of Governmental
Industrial Hygienists [13] is at the high level of 5 parts per million
(ppm), approximately 13,000 yg/m3. Studies with human subjects cited in
-265-
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this report indicate the following effects of S02 with increasing con-
centration:
3-5 ppm - Noticable odor
8-12 ppm - Irritation of the mucous membranes, i.e.,
nose, eyes, etc.
13 ppm - Increased airway resistance
150 ppm - Increased incidence of respiratory disease,
hospitalization, deaths from all causes,
etc.
These are considerably higher thresholds than those reported in the NAPCA
data. TLV's are established for use in industrial contexts and are not
necessarily applicable to the nonworkplace environment in which exposures
may be of much greater duration and in which particularly susceptible
populations of children, ill and elderly people may be found.
Wolff et al. [705] subjected healthy humans to concentrations
of 5 ppm of S02 and found a slight decrease in the maximal mid-expiratory
flow rate but no significant effect on muco-ciliary clearance.
The TLV of sulfuric acid is 1 mg/m3 [14] since above this level
it causes respiratory irritation and over prolonged periods, dental injury.
In a study by Amdur et al. [11], in which normal human subjects were
exposed to the inhalation of sulfuric acid mist for 5-15 minutes, concen-
3
trations below 1 mg/m could not be detected by odor, taste, or irrita-
3
tion. A concentration of 3 mg/m was noticed by most subjects, and
o
5 mg/m resulted in irritation of the respiratory tract. Raule [511]
noted that workers chronically exposed to HoSO* may show lesions of the
skin, tracheobronchitis, stomatitis, conjunctivitis and gastritis. There
-266-
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is also evidence that chronic exposure causes corrosion of dental
enamel.
Concern with adverse effects of sulfate aerosols is strength-
ened by results of studies by Amdur and Corn [10] and Davies [150] which revealed
a significant increase in pulmonary airflow resistance in guinea pigs
exposed to sulfuric acid droplets and particles of zinc ammonium sulfate,
zinc sulfate, and ammonium sulfate.
In the light of the various reports of concentration levels at
which sulfur dioxide is "associated with adverse health effects, it is
appropriate to recapitulate here some of the evidence for the existence
of elevated S02 concentrations in indoor, nonworkplace environments. The
highest 24-hour S02 concentrations found indoors have been on the order
of 850 yg/m3 [681] and 1300 yg/m3 [359] found in Moscow and London, respec-
tively. In Cincinnati indoor concentrations as high as 500 yg/m3 were
reported [564], In studies conducted in Hartford, Connecticut, seasonal
averages of S02 concentrations were found as high as 182 yg/m3 [714].
Information on indoor sulfate and sulfuric acid concentrations in non-
industrial environments is not yet available. Though S02 concentrations
have been shown to be lower indoors than outdoors, the mechanism for S02
depletion may be a cause for concern since the process involves the oxi-
dation of S02 to sulfates with potential hydration to form acid mists.
In summary, the combination of atmospheric sulfur oxide, its
conversion products, and suspended particulates, appears to present a
clear health hazard at commonly realized ambient levels, although the
role of sulfur dioxide alone has not been clearly established. If recent
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-------
work is correct, sulfates present a greater health hazard than SOg.
There is evidence that chronic exposure to sulfates may produce serious
extrapulmonary effects, particularly neoplasms in the body systems
involved in clearance.
Sulfates which tend toward micron and submicron sized aerosols
may be important indoor pollutants. While SOg is reactive and may pose
a minor indoor problem, it tends to disappear quite rapidly [144]. Sus-
pended sulfates may remain at levels more equal to outside ambient levels
and therefore present a more persistent hazard. Further research is indi-
cated on, the issues of chemical composition and concentration of indoor
sulfates, and the human clearance of sulfates.
8.2 CARBON MONOXIDE
Carbon monoxide (CO) has been the most extensively studied of
all pollutants in terms of toxicological aspects and this research seems
to be continuing to a greater degree than for any other pollutant. The
major aspect of the present interest is in effects on the cardiovascular
system. Because the characteristics of CO health effects are so generally
known, only a brief summary of salient points will be included here.
As previously noted in Section 3.0, while in some respects CO
concentrations indoors are similar to those of S02, there is an important
difference. CO is relatively unreactive and decays slowly, compared with
S02- Since it is also generated indoors (from gas-fired appliances, leaky
furnaces and chimneys, and from attached garages), it is an extremely
important indoor pollutant.
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The TLV for carbon monoxide is 50 ppm (approximately 55 mg/m3)
[14]. The inhalation of carbon monoxide, a colorless, odorless gas of
specific gravity similar to that of air, causes asphyxiation (anoxia,
hypoxia) by forming metastable chemical compounds, primarily with hemo-
globin and secondarily, with other biochemical constituents which in a
complex manner reduces the availability of oxygen for other cellular sys-
tems of the body. The resulting physiologic effect is similar to, but in
some respects more serious than, a simple lack of oxygen caused by a reduced
partial pressure in inspired air.
The equilibrium concentration of carbon monoxide with the hemo-
globin of the blood is substantially complete for individuals at work in
6 to 8 hours [13]. When the air contains 100 ppm of CO, the blood at
equilibrium will contain 18-20 percent of carboxyhemoglobin (COHb); if
air has 50 ppm CO, blood will have 8-10 percent COHb; for air of 25-30 ppm
CO, there will be a 4-5 percent COHb.
The effect of carbon monoxide exposure on man is enhanced by
factors such as heavy labor, high environmental temperature, and increasing
altitude (above 2000 feet). Susceptibility is greatest in the aged, the
very young, those with cardiac or chronic respiratory disease and with
pregnancy [269]. However, some individuals, particularly cigarette smokers,
have an increased tolerance to CO. The latter may tolerate COHb values of
5-10 percent (with its appreciable chemical effect) as compared to non-
exposed adults.
-269-
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The approximate relationships between ambient CO concentrations,*
the percent of COHb in the blood, and the resultant symptoms, are as
follows:
Atmospheric CO - ppm COHb Concentrations - % Principal Symptoms
5° 7 Slight headache in some
100 12 Moderate headache and
dizziness
250 25 Severe headache and
dizziness
500 45 Nausea, vomiting, pos-
sible collapse
1000 60 Coma
10000 95 Death
>
An ad hoc committee, established in 1972 by the Bureau of
Community Environmental Management, reviewed the effects of CO on human
health with the specific objective of developing recommendations for
residential standards. They concluded that continuous exposure should
not exceed 15 ppm (resulting in about 2.6 percent COHb at equilibrium
in nonsmokers). This level was considered to allow both for the higher
CO concentration tolerance of smokers and the increased susceptibility
of cardiac patients. Considering the ambient standard to be 9 ppm for
8 hours, indoor concentrations should not be allowed to raise the base-
line air content by more than 6 ppm. For comparison, 15 ppm has been
proposed as the short-term public limit by the National Academy of
Sciences [447].
Occupational Health and Safety, International Labour Office, Geneva, Switzerland, 1972.
-270-
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Stewart [610] recently reviewed evidence pertaining to the
effects of low CO concentrations on man. CO is eliminated nearly com-
pletely by the lungs. In healthy, sedentary adults at sea level the
biological half-life is 4 to 5 hours; this time increases with altitude.
Increased blood flow, to compensate for oxygen reduction, is noted at
1-5 percent COHb.and may be significant for those with substantially
impaired cardiac reserve, Reduction in exercise tolerance is noted in
normal individuals, and less exertion is required to produce anginal
pain in cardiacs at 5-9 percent COHb. Above this level of COHb, definite
symptoms and neurological changes are observed and increased mortality
in those with severe cardiac disease is possible. For reference, exposure
of a sedentary adult with normal physiology and under standard conditions
of 50 ppm for 5 hours would raise COHb to about 5 percent.
/
A study of the possible correlation of ambient CO concentrations
and the incidence of myocardial infarction and sudden death in Baltimore
[361], did not support other evidence that CO exposure was a major
factor. The risk of sudden death was higher in smokers than nonsmokers,
and those who had formerly resided in high ambient CO areas had higher
post-mortem COHb levels. The authors postulated that there may be a time
lag between an increase .in ambient CO concentrations and its deleterious
effect in the human. Kuller et al.- [361] did not find marked differences
in post-mortem COHb levels in individuals with and without acute coronary
lesions, nor were COHb levels related to the degree of coronary stenosis.
Radford et al. [505] studied hospital admissions for chest pain and concluded
that the clinical course and severity of infarction among smokers and nonsmokers
-271-
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was consistent with both an acute and a chronic effect of CO exposure.
However, other constituents of cigarette smoke may be of equal or greater
importance. -Both the Kuller and Radford reports emphasized the difficulty
in establishing the independent roles of environmental CO and smoking in
any study of the low-level effects of CO. While neurological and cardiac
lesions have been attributed to chronic CO exposure by some, the majority
of investigators have not reported such pathological changes.
Figure 26 adapted from Stern et al. [607] shows the relations
between concentration levels of CO and associated health effects.
mg/m1 (High concentrations, 30-120 sec) physiologic
stress on heart patients, COHb above 5»
120
100
80
70
60
SO
40
30
(Intermittently through face mask) impairment
in performance psychomotor tests at 5% COHb
(Nonsmokers, 90 mln) impairment time-interval
discrimination, increases COHb by 2%
(Nonsmokers, 8-12 hrs) 5% COHb, Impaired per-
formance on psychomotor tests, physiologic
stress on heart patients
1.15 mg/m* CO,= 1 ppra (vol)
Figure 26. Reference data for carbon monoxide effects.
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The special hazards of carbon monoxide in indoor environments are
widely known. Studies have shown indoor concentrations of carbon monoxide at
potentially hazardous levels to be a frequent occurrence. The impact of cigar-
ette smoking on indoor CO levels has been often cited [88, 610, 531, 270, 40].
Internal combustion engines as sources of indoor CO produced symptoms of drows-
iness, headache and nausea in school children which led teams of investigators
to monitor for carbon monoxide in school buses and ice-skating rinks [335, 336],
Radford reported 1 percent of the sample of 302 old houses in Baltimore as
having carbon monoxide levels greater than 50 ppm, attributed to faulty indoor
combustion sources [504]. Biersteker and Yocom [69, 712] found similar faulty
combustion sources in a small percent of the samples surveyed. These findings
are of particular concern if extrapolated to a large population using stoves,
heating systems and space heaters of which even a small percentage is faulty.
^
8.3 CARBON DIOXIDE
Carbon dioxide, while not normally considered a hazardous con-
stituent of the air (with a normal ambient concentration above 325 ppm
[557], under certain unusual circumstances can be present in the indoor
environment in asphyxiating concentrations. There have been a number of
instances reported, usually occupational in nature, where C02 has caused
fatalities. The normal symptoms of excessive COg exposure as reported by
Hamilton and Hardy [266] are attributable to oxygen deprivation. These
authors also state that "unconsciousness and death do not occur unless
oxygen is as low as 5 percent - unless the victim makes strenuous exertion,
in which case death may come while there is still 8 percent oxygen" [266].
Carbon dioxide has been reported to be a "weak narcotic at 30,000 ppm ...
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at 50,000 ppm, a 30-minute exposure produces signs of intoxication, and at
70,000 to 100,000 ppm, unconsciousness in a few minutes" [266J. The thresh-
old limit value has been set at 5,000 ppm for an eight-hour exposure [14].
The personnel of a submarine experienced chronic fatigue when C02 levels
reached 3 to 15 percent (30,000 to 150,000 ppm) for several weeks [374].
In the same report, LaVerne et al. state that COg is easily "eliminated
from the body and brain by reflex hyperventilation within seconds after
treatment, thereby preventing cumulative toxic side effects."
Carbon dioxide has been used in varying concentrations for many
different therapeutic reasons for almost 50 years. CO^ is a cerebrovas-
cular dilator and respiratory stimulant and has been used in the fields
of pediatrics and geriatrics as well as for the treatment of narcotic
addiction and alcoholism [374].
The normal ambient concentration of COg is approximately
325 ppm. Ishido [326] has found indoor concentrations of C02 ranging
from 1 to 10 times the outdoor concentration. Therefore the C02 com-
prised from 0.03 to 0.32 percent (300 to 3,200 ppm) of the indoor air
[326]. Although these concentrations are not as high as the TLV, the
potential exposure could be for longer periods of time than the 8 hours
that the TLV's are based upon. Therefore, as LaVerne et al. stated
"it appears that (X^ inhalation, whether therapeutic or nontherapeutic
can be as safe or as dangerous as the conditions created in each specific
situation" [374].
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8.4 NITROGEN OXIDES
The pollutants of concern among the nitrogen oxides are nitrogen
dioxide (NOg), nitric oxide (NO), nitric acid, and acid salts (nitrates).
Nitric oxide (NO) peak ambient levels are not generally considered to pre-
sent a direct health hazard; the greatest toxic potential of NO at these
concentrations is related to its tendency to undergo oxidation to nitrogen
dioxide [646]. The evidence for respiratory disease associated with N02 is
cited below. Nitrogen oxide reaction products have been associated with
equipment corrosion but biological effects are generally not well-researched.
As contrasted with sulfates, nitrates appear to have a more uniform particle
size distribution and the proportion available as respirable aerosols (<3.5y)
may be smaller [606].
Few toxicological or epidemiological studies of atmospheric
nitrogen oxides are available. Figure 27 from Stern et al. [607] indicates
the parameters used to establish the National Ambient Air Quality Standards
by NAPCA [646]. The original study reported reduced respiratory function
in children, and increased respiratory illness among families, in the high
N0£ area [568]. Because the original aerometric data were considered
unreliable, N02 data for the previous year were used in a subsequent anal-
ysis by Shy et al. [567] providing similar results at slightly different
concentrations. Subsequent studies of the same Chattanooga areas were
conducted by Pearlman et al. [482] and Chapman et al. [121]. Pearlman
reported an increased incidence of bronchitis among school children in the
defined high and intermediate N02 areas after two and three years of resi-
dence. No significant difference was found in the incidence of croup or
pneumonia, or in reported hospitalization for lower respiratory tract
-275-
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(2 hr at 20,200-94,000 Mg/ms)
tissue changes in lungs,
heart, kidney, etc.- Monkeys
5000 - -
(3 wks) polycythemia - Rats, monkeys
(Life) epithelial changes - Rats
(1 hr) changes lung collagen - Rabbits
(Life) bronchlolar hypertrophy - Rats
2000 - -
1000
(4 hr) changes lung mast cells - Rats
alveolar distension mice
(4 hr/day) changes lung collagen - Rabbits
500 - -
200- -
100 -1-
(10 min) increased airway resistance
(21-48 hr) visible leaf damage in
sensitive vegetation
- (35 days) navel orange leaf abcission
Human olfactory threshold
(2*3 yrs) increased respiratory disease
(2-3 yrs) increased bronchitis in children
Figure 27. Reference data for nitrogen dioxide air quality criteria [607].
-276-
-------
illness. Chapman found no association between current or past pollution
levels and the prevalence of chronic respiratory disease among parents of
high school students residing in the three areas.
The original study of Shy and his associates was criticized by
Warner and Stevens [677] because no attempt was made to control for acid
mists, which were probably present in significant concentrations. Pearlman
et al. [482] in their retrospective study found that for the intermediate
3
and high N02 areas, suspended nitrates ranged from 2.6-5.8 yg/m (24-hour
mean over a six-month period). It is interesting to note that bronchitis
prevalence was not related linearly to any of the pollutant measures, and
that there could have been different contributions of pollutants in the
various residential areas.
From a review of (unpublished) data produced in subsequent
epidemiological studies of Chattanooga, Riggan [521] has proposed that
3
"repeated short-term exposures of 228-815 yg/m N02 may contribute to
excess risk of acute respiratory disease in the absence of excessive
long-term exposures." He points to the work of Coffin et al. [128] in
which rats were challenged with bacilli after varying N02 exposures.
This study showed that in short-term exposure to N02, the concentration
employed has a much greater influence than the duration of exposure, for
equivalent exposures (i.e., for equal products of concentration and
time). Other work [129, 229] using an infectivity model in experimental
animals, indicates that exposure to N02 and 0^ may decrease resistance
to respiratory infection via destructive action on pulmonary alveolar
macrophages - i.e., reduction in number, in phagocytic competence, in
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viability and enzymatic function. However, since the effect of a single
dose of an oxidant on the macrophages is known to last approximately
24 hours (until they are replaced), the authors suggest that additional
factors which enhance pulmonary infectivity are present - particularly
with intermittent exposure to N02-
French [222] after reviewing published and unpublished data
from the Chattanooga studies, concludes that the findings suggest:
1. Exposure to prolonged levels of nitrogen dioxide,
ranging from 113 to 395 yg/m3, in combination with
short-term exposures of 301-1203 yg/m3 may con-
tribute to excess risk of acute respiratory disease
and the residual effects from this exposure may
last for as long as four years.
2. Repeated short-term exposures of 228 to 815 ug/m
may contribute to excess risk of acute respiratory
disease in the absence of excessive long-term
exposures.
3. Prior high short-term and long-term exposures to
N02. coupled with continuous excessive short-term
exposures, might trigger the onset of chronic res-
piratory disease symptoms.
Riggan [521] has developed a protocol for the prospective study
of acute respiratory disease and its variation related to peak hourly and
daily exposures to N02 and other pollutants. The study will be conducted
in several locations in the Los Angeles basin to provide controls and a
variety of pollutant combinations, including oxidants and sulfur oxides.
Data collection is scheduled to begin in late 1976, with a preliminary
report expected by February 1978.
The TLV established for N02 by the American Conference of
Governmental Industrial Hygienists is 5 ppm (approximately 9 mg/m ) [14],
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This ceiling was to some extent established to minimize the risk of
accelerating lung tumor development.
o
The TLV for nitric acid is 2 ppm (approximately 5 mg/m ) [14].
In practice HNO-j is usually found in conjunction with nitrogen dioxide.
According to Fairhall, continued exposure to the vapor and mist of
nitric acid may result in chronic bronchitis and more severe exposure,
to chemical pneumonitis [199]. It may also erode the dental enamel [402].
Two recent studies which suggest a statistical association
between mortality and exposure to nitrogen oxides have been identified.
Sprey and Takacs [597] in analyzing data for 42 cities, found a strong
association between NOp and median disease-specific mortality rates for
hypertensive and arteriosclerotic heart disease, and for lung cancer.
There was a fairly linear relationship for each cause of death for NOp
levels, increasing from 0.3 to 0.8 ppm. 'Analysis of pooled variables
and of independent age groups, subsequently showed arteriosclerotic
heart disease to be associated with an interrelationship of NOp and ambient
sulfate levels. (Because of the strong involvement of smoking in pulmonary
carcinogenesis, discussion of air pollution and lung cancer is considered
in more detail later.) In a similar type of investigation, Lave and Seskin
[370] have reported an association between nitric oxide (NO) levels and
daily mortality in Chicago (in Hershaft et al. [286]).
Much about the mechanisms and degree of nitrogen oxide effects
is not well understood. Although apparently less acutely toxic than
ozone, NOp is considered to have more similarities with 0^ than S02 in
terms of biological actions. Aviado and Salem [47] point out that S02
-279-
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and S03 are believed to exert their primary effects on the airways while
N02 and 03 exert their primary effects on pulmonary capillaries. A
*
difference in solubility is possibly one reason, with the relatively
insoluble N02 and 03 able to penetrate deeply into the lung without
appreciable loss in inspired concentration. Stockinger and Coffin [616]
have listed a number of apparent analogies and dissimilarities in actions
of N02 and 03. Among differences cited are the high threshold of acute
lung response, the relatively low toxicity, and the short-acting toler-
ance of N02. Most animal studies and observations on human responses to
peak exposures have been at concentrations far exceeding typical ambient
levels. It is understood that chamber experiments are now being conducted
by EPA which will include N02 alone and in combinations with other major
pollutants. With the limited epidemiological research, little information
is available on sensitivity differentials. Presumably those groups mentioned
for S02 would also be sensitive to N02. It has been reported that nitrogen
oxides can result in increased methemoglobin so that anemics may be more
susceptible. This effect may be due to the formation of organic nitrates
(obtained by combining the N02 group with an organic radical) which are
transformed into nitrates in the body. This promotes the formation of
methemoglobin.*
Seinfeld [557] has stated that N02 is transformed in the lungs
to nitrosamines, some of which are suspected human carcinogens. Johnson
[339] has suggested that nitrous oxide (N20), if metabolized, could provide
the nitrating source for nitrosamine formation in gastric juice or other
* Occupational Health and Safety, International Labour Office, Geneva, Switzerland, 1972.
-280-
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acid substances in the body. He^points out that there are many secondary
amines in our diet (e.g., proline) and in tobacco smoke (e.g., pyrrolidine),
of which some nitrosamine forms have been shown to be potent carcinogens
in various animal systems. Johnson hypothesizes that this mechanism may
be the causative agent in excess cancer mortality among anesthesiologists.
The hazard to human health from nitrogen oxides in indoor air
may be assessed in the light of reported indoor concentrations. Peak one-
hour average concentrations of N02 have been found in kitchens during gas
2
appliance operations to range between 450 to 950 yg/m [178, 184, 308].
Peak concentrations of N02 less than one hour in duration, have been
reported as high as 1900 ug/m3 (1 ppm) [178] and 2800 yg/m3 (1.5 ppm)
[184]. These values cannot be readily compared with the criteria which
established the National Ambient Air Quality Standard (NAAQS) for N02
since the reference data were concerned with chronic respiratory
illnesses. These indoor~N02 data, however, may be compared with
recent conclusions regarding short-term N02 exposures reported by
Riggan [521] and French [222]. On reviewing the earlier N02 health effects
criteria, principally the Chattanooga Study, the authors of those studies
report that repeated short-term exposures to N02 contribute to an excess
risk of acute respiratory disease in the absence of excessive long-term
exposure. Riggan proposed a range of short-term exposures to N02 between
228 and 815 yg/m . The range of high one-hour average N02 concentrations
reported in kitchens where gas-fired appliances are in operation, as
summarized above, are within this range of potential risk to acute respira-
tory disease. Although a survey by the American Gas Institute does not
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lend support to this relationship, the AGI investigators did not monitor
N02 in the homes where the survey was conducted.
Two studies have compared the incidence of reported respiratory
illness in households cooking with gas and electricity. Eaton [179]
found an association with the use of gas stoves but Keller et al. [349]
could determine no significant difference among households. Further
field studies to determine short-term N02 exposure and effects are required
particularly in homes using gas-fired appliances. Additionally, nitric
add, nitrate, and nitrosamine concentrations should be monitored.
Studies of the blood level concentrations of methemoglobin of residents
of homes with and without gas-fired appliances is also indicated.
8.5 PHOTOCHEMICAL OXIDANTS
This section covers oxidants (excepting N02) that result from
photochemical atmospheric reactions and their precursor gaseous hydrocarbons.
The principal individual compounds in this class of primary interest as
potential hazards to human health at ambient levels are:
Ozone (03)
Peroxyacetyl nitrates - peroxyacetyl nitrate (PAN)
and peroxybenzoyl nitrate (PBzN)
Aldehydes - formaldehyde (HCHO) and acrolein
(CH2CHCHO).
As previously described (Section 4) ozone and PAN are secondary
pollutants in the ambient air, typically arising from interactions of
automobile-generated hydrocarbons and NOX emissions in the presence of
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sunlight. Ozone does not usually originate in significant quantities
in indoor environments. Ozone and PAN are highly reactive and, like SOp
do not persist in high concentrations indoors even when outdoor concentra-
tions are high, because of rapid decay through absorption on indoor
surfaces.
Many other organic conversion compounds are known or are hypoth-
esized to exist in polluted air (e.g., organic peroxides, ketones) but not
at concentrations for which effects on man have been documented. Similarly,
many individual hydrocarbons have been identified in polluted air which
are biologically active but human responses have not been found below
concentrations of several hundred ppm. The precursor ambient gaseous
hydrocarbons are considered important only as an index of potential photo-
chemical conversion [644]. However, before these low-concentration pollu-
tants are dismissed, two points concerning.their toxicity should be made.
First, the hazard from possible cumulative effects of repeated exposures
at ambient levels is unknown. It has been demonstrated that repeated
sublethal doses (one-fifth LD5Q) of hydrogen peroxide can result in a
cumulative effect and eventually death in experimental animals [616].
Second, many of these chemicals or their homologs are components of house-
hold and industrial products which are used in concentrations within the
toxic range. Hazards from vapors and aerosols generated by the use of
such agents will be taken up in subsequent sections.
Ozone has been found to be the major component of observed
ambient levels of the photochemical oxidants and therefore is used as
the standard in the measurement of total oxidants. For this reason,
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oxidants and ozone are frequently used interchangably in exposure-response
studies, although varying concentrations of other oxidants with different
biological actions may be present. The national standard for ambient
ozone and oxidants is the same.
Figure 28, from Stern et al. [607], presents the data base used
in development of air quality criteria for ozone and oxidants by NAPCA
[644]. Because of its relative toxicity, the one-hour standard for oxidants
is about one-fourth that of S02 and one-third of the California standard
for N0« (0.25 ppm, one hour). The standard was based on level of oxidants
associated with eye irritation. Few epidemiological studies were avail-
able and only a small number of them showed an association of deleterious
health effects with oxidants: e.g., increased attacks in a small proportion
of asthma patients and impairment of performance in student athletes (in
the latter case involving oxidants and particulates). Sterling et al.
[605] found a significant correlation between the concentration.of ambient
oxidants and hospital admissions for cardiovascular and respiratory con-
ditions. However, they also noted similar strong associations for S02>
N02, and particulate matter. Data analyzed by Wayne and Wehrle [679]
showed no significant association between oxidant levels and school absen-
teeism due to respiratory illness.
According to Griswold et al. [255] ozone exposures for two hours
at an average concentration of 1.5 ppm 03 resulted in a 20 percent reduction
of the timed vital capacity. In addition to its more serious effects, air
concentrations of ozone in excess of a few tenths ppm causes headache and
dryness of mucous membranes in exposed individuals [693]. After review
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Oxidant
(Mg/ms) Ozone
F 400° (2 hr) Reduced VC, severe cough, in-
ability to concentrate
20
Ozone = 0.01 ppm (vol)
(Dally maximum) respiratory problems
TLV(8-hr) 200/jg/m3
(Peak values) eye irritation
(1 hr) Impaired athlete performance
(4 hr) Vegetation damage
(2 hr) Impaired diffusion capacity (DLCO)
- 1000 (3 hr/day) Changes in pulmanary function
- 800
- 600 (8 hr) Respiratory irritation and chest
constriction
3000
-400
- 300
(8 hr) Small decrements in VC, FRC,
DLCO
200 (1 hr) Increased airway resistance
(3 hr) Increased animal susceptibility
bacteria
- 100
-80
60 (8 hr) Vegetation damage
(1 hr) Cracking of stretched rubber, odor
40 detection in 5 min
Figure 28. Air quality criteria for photochemical oxidants [607] .
-285-
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of the research and industrial health experience up to 1964 [615], it was
pointed out that 0^ is radiomimetic and thus with continuous exposure
(eight hours daily) to concentrations not acutely injurious per se, may
be associated with premature aging and a shortened life span.
Hammer et al. [268] compared the daily percent of nursing students
reporting each of several symptoms with the daily maximum concentration of
oxidants. Patterns for several of the symptoms, particularly eye discomfort,
conformed with oxidant levels. Further analysis of the symptom data [267]
showed that incidence could not be attributed to carbon monoxide, nitrogen
dioxide, or elevated temperature. The investigators developed oxidant
thresholds for several symptoms: eye discomfort (0.15 ppm); cough (0.26 ppm);
chest discomfort (0.30 ppm); and headache (0.50 ppm). A TLV for ozone estab-
lished by the American Conference of Governmental Industrial Hygienists
o
[14] is 0.1 ppm (approximately 200 yg/m ).
Symptoms at various oxidant concentrations can be compared with
results found in chamber studies. As a recent example, Hackney et al.
[259] conducted a series of experiments with adult male volunteers
who were subjected to short-duration (two and four hours) exposures to
various levels of ozone. While the findings are too complex to cover
fully, selected results are summarized in Table 42.
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TABIE 42. EFFECTS OF CONTROLLED OZONE EXPOSURE ON ADULT MALES [259]
Croup
#1- Normal
#2 - Reactive
#3 - Normal
Reactive
#4 - One Normal,
Five Reactive
85 - Mixed
One Reactive
03 (pphm)
30-SO*
25
37
50
50
25**
37
Duration
(Hours)
4
2
2
4*2
2
2
2
Respiratory
Physiology-
Few changes
One measure
Mild
Marked
F ew or none
Marked (2nd
day)
Few or cone
None impor-
tant
Marked
Symptoms
Few
None
Severe
Marked
Few or none
Marked
None
Marked
Blood
Biochemistry
NR
MR
Oxidative chacKjej
Erythrocyte fra-
gility-
Few or none
Oxidative changes
Oxidative changes
* 03, O3 + NO2 and 03 + NO2 + CO
** O3 * NO2 + CO
> NR Not Reported
Reactive (sensitive) subjects, as defined by history or testing,
developed such severe symptoms after exposure to 60 pphm for four hours,
that subsequent exposure was shortened to two hours, even though normal
subjects reported few symptoms. At 37 pphm (two hours), symptoms in some
reactive subjects were more severe than at 50 pphm (two hours), but respira-
tory system changes were less marked. Normal subjects exhibited few important
symptoms or signs at any level, for either time duration, or with various
pollutant mixes. Oxidative blood changes were found in reactive subjects
at 37 and 50 pphm, and increased erythrocyte fragility at 50 pphm. The
decrements in pulmonary function at 37 pphm (two hours) are similar to
those reported by Bates et al. [56] and Hazucha et al. [281].
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The other agents have not been studied at ambient levels. PAN
has been reported to approach eye irritation threshold at a concentration
of 0.5 ppm in 12 minutes and an increased oxygen uptake (during exercise)
resulted at a concentration of 0.3 ppm [616]. Formaldehyde is known to
induce hypersensitivity and to depress ciliary activity. The irritation
threshold of mucous membranes for formaldehyde has been reported to be
between 0.01 and 1.0 ppm and for acrolein as low as 0.25 ppm. As these
agents are not consistently proportional to ozone it may be suitable to
investigate their irritant properties separately under ambient conditions.
No information was identified on long-term, low concentration effects of
these agents.
A survey of the origins and consequences of atmospheric pollution
by vapor-phase organic pollutants published in 1976 by the National
Research Council [460] notes that the photochemical reaction products of
organic pollutants present potential hazards of mutagenicity as well as
the unfavorable health effects of ozone, lachrymators such as PAN and
PBzN, and the aldehydes.
The hazard to human health from ozone in indoor concentrations
may be assessed by comparing the results of these health effects studies
to the levels of ozone which researchers have reported inside buildings.
Indoor one hour ozone and oxidant concentrations have been reported to
range as high as 300 to 500 yg/m3 (14-16 pphm) in a-surgical intensive
care unit. The buildings where ozone or oxidant values were reported
in this range were reasonably well ventilated. Inside ozone or oxidant
values in residential buildings and schools were between 50 to 80 percent
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of those found outdoors [561, 626, 627]. In comparison with ozone criteria
associated with adverse health effects (Figure 28), these values are in
excess of those associated with eye irritation and increased airway
resistance. However, the relative indoor-outdoor relationship indicates
that significant protection from ambient levels may be achieved in air con-
ditioned buildings.
Further investigation of the effects of ozone and other oxidants
seem Indicated Including:
t The synergistic health effects of oxidants in
the presence of particulates, sulfates, and
nitrates
0 The long-term effects on those chronically
exposed to typical ambient levels.
8.6 ORGANIC POLLUTANTS
The term "organic pollutants" as used here refers principally
to the diverse class of manufactured organic chemicals which may enter
the air (1) 1n the vapor or liquid phase of aerosol spray operation,
(2) through vaporization from the surface of liquid solvents, fuels,
household cleaners and similar products, or (3) as a residual dust from
pesticide use. Organic pollutants also include complex aldehydes which
may arise from cooking operations. The term "organic pollutants" in
this context does not include the photochemical oxidants which have been
considered earlier, nor does it include the biological and allergenic
materials which have not been examined in this report.
The nonphotochemical organic air pollutants do not fit neatly
Into categories of gases and particulates. They may occur in both phases,
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even simultaneously in the case of aerosol sprays. As particulates they
may be in the form of liquid droplets in an aerosol or as solid particles
for some pesticides.
Organics are contained in a wide variety of products used in
homes, offices, and schools. They may be present in either the active
ingredients or the propel 1 ants of packaged aerosol sprays, as well as
being used directly in liquid applications. Many of them contain chlorine,
bromine, or fluorine, forming a general class known as halogenated hydro-
carbons. These substances in general can cause liver and respiratory
system pathology and are neurotoxic. Several (carbon tetrachloride,
trichlorethylene, chloroform, vinyl chloride) have produced cancer in
animals. The degree of toxicity of the organics varies considerably.
The discussion of health effects of organic pollutants may be somewhat
arbitrarily considered under headings of solvents and fuels, aerosol
propel 1 ants, and pesticides and combinations of pollutants.
8.6.1 Solvents and Fuels
One of the major sources of exposure to toxic chemicals in
indoor spaces is through the endless variety of products used as fuels,
cleaners, paint and paint products, laundry products and hobby materials.
Other than their use as fuels (propane, butane, gasoline, kerosine, etc.),
most of these chemicals are used directly as solvents (degreasers, paint
removers) or are solvent components of compounds (paint thinners, kitchen
and bathroom cleaners, plastic and rubber cements). Many are in gaseous
form; many others volatize readily or are used as sprays. Little informa-
tion pertinent to evaluation of human hazards in nonindustrial exposure
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situations are available, so that we must turn to studies made for work-
place settings.
Table 43 lists health-related information for a number of
chemicals commonly found in domestic products to illustrate the variation
in type, toxicity and dose-response data. Threshold Limit Values (TLV's)
given are recommendations for 8-hour average time weighted exposure for
healthy adults assuming a 40-hour work week. Therefore, the TLV's are
only crude proxy guidelines at best for household exposures and perhaps
several times higher than a "safe" level, particularly when children and
more susceptible persons are involved. The exposure-response data given
is the information available concerning the lowest concentrations at which
human effects were observed. Most of these studies are on short-term
exposures and acute effects. Data on long-term exposure is seldom found.
Many of the chemicals in this section fall into a number of
groups which have common exposure characteristics and toxic properties.
The review that follows was drawn primarily from Hamilton and Hardy
[266].
Saturated Aliphatic Hydrocarbons - Of interest in this group
are the gases methane, propane and butane, and liquids from pentanes
(C5) through C,g compounds. Methane, the principal component of natural
gas, is biologically inert. In general the series from propane (Cg)
through the octanes (Cg) show increasingly strong narcotic properties,
although the thresholds are very high. Sources of vapors from compounds
containing liquid hydrocarbons in the series from pentane through octane
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TABLE 43. ILLUSTRATIVE HEALTH INFORMATION ON SOME HOUSEHOLD SOLVENTS AND CLEANERS
Compound
Use
TLV*
Exposure-Response Data*
i
ro
10
ro
Methylene chloride
Peichlorethylene
VMGP Naphtha
Benzol (benzene)
Toluol (toluene)
Xylol (xylene)
Methanol
Acetone
Ethyl ether
Sodium hydroxide
Ammonia
Turpentine
Paint remover
Cleaning fluid
Paint thinner
Lacquer and
cement
solvents
Shellac and
varnish thinner
Lacquer
solvent
Lacquer, wax,
plastic solvent
Drain cleaner
Window
cleaner
Painting
200 ppm (720 mg/m3)
100 ppm (670 mg/m3)
200 ppm (900 mg/m3)
10 ppm (30 mg/m3)-Skin
200 ppm (260 mg/m3)-Skin
1000 ppm (2400 mg/m3)
400 ppm (1200 mg/m3)
2 mg/m3
25 ppm (18 mg/m3)
100 ppm (560 mg/m3)
180-200 ppm per day results in increment of 4.5 percent COHb.
Narcosis above 4,000 ppm. Brain damage reported from repeated
peaks above 500 ppm.
100 ppm for 7 hours produced narcotic effect, headache, mild eye
and respiratory irritation. Marked narcotic effect above 200 ppm
for 3 hours.
Multiple hydrocarbon content (TLV based in nonane, xylene).
Myelotoxicant. Skin absorption can produce chronic poisoning.
Headache, nausea, narcosis above 200 ppm. May contain benzene
200 ppm irritating. CI, neurological and vascular effects reported
in workers. May contain 6-15 percent ethyl benzene.
No worker injury at average 160-780 ppm. Repeated exposure above
3,000 ppm may result in cumulative body concentration.
Minor eye and nose irritation above 2500 ppm.
Nasal irritation above 200 ppm. No worker injury demonstrated from
regular exposure of 500-1000 ppm. Chronic effects noted after long-
term exposure.
Upper respiratory irritant at 2 mg/m3.
Rat ciliary motion stopped at 3 ppm. Detection at 1-5 ppm. Eye
and nasal irritation at 20-25 ppm.
Respiratory irritation at 75 ppm. Marked irritation and nausea occur
above 750 ppm for several hours.
* TLVs and Response Data from Documentation of the Threshold Limit Values [14] .
-------
are mixtures such as petroleum ether, benzine, petroleum naphtha, gasoline,
mineral spirits, Stoddard solvent and varsol - which are commonly found
in household use. The vapors are moderately irritating and have narcotic
effects typical of heptane or octane. However, these mixtures may contain
other chemicals such as benzene which are of much greater significance
toxicologically.
Aromatic Hydrocarbons - The important chemicals here are benzene,
toluene and xylene, which are used as plastic and rubber solvents. Many
hydrocarbon mixtures, and-in particular coal- and petroleum-derived sol-
vents, may contain unknown quantities of benzene. Besides the central
nervous system depression usual to hydrocarbons, benzene exposure can
result in chronic poisoning with insidious onset, resulting in aplastic
anemia and possibly leukemia. Toluene and the xylenes are less toxic and
similar in their effects, which are primarily narcotic. Lethal cardiac
arrhythmias have resulted in "glue sniffers." There is some evidence that
toluene also may be a myelotoxicant after chronic exposure but a causal
association has not been established.
Chlorinated Hydrocarbons - This group includes most of the sol-
vents routinely encountered in cleaning and painting products. Toxic
levels vary considerably. Two of these agents, carbon tetrachloride and
chloroform, have been identified as carcinogens in laboratory animals.
Toxic manifestations reported for the various chlorinated hydrocarbons
have included eye and respiratory irritation, neurasthenia, cardiac irreg-
ularities, and liver damage. The extreme volatility of these compounds
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permits rapid achievement of significant concentrations within a short
time. Absorbed dose varies with metabolism. For example, most, like
tetrachloroethylene, are exhaled unchanged. Methylene chloride however
is almost completely metabolized to carbon monoxide, a unique and
dangerous characteristic [616].
Other Solvent Compounds - Other chemicals of interest are the
alcohols, ketones and ethers, esters, acids and caustics. Methanol is
a component of lacquer thinners and canned heating preparations (sterno).
Eye and respiratory irritation may result from exposure to vapors but
systemic intoxication is unlikely without accidental ingestion. Ketones
and ethers are common lacquer solvents. Acetone is the most frequently
encountered. Others of this group are more irritating, but severe com-
plaints have occurred only a very high occupational levels. Bis-
chloromethylether (BCME) has been established as a human carcinogen but
is unlikely to be found outside of industrial settings or laboratories.
Aliphatic esters, primarily ethyl acetate and butyl acetate, are used
as lacquer thinners. Vapors are irritative but other significant toxico-
logical effects have not been established. Several types of acids and
caustics may be found in the home: sulfuric, nitric and hydrochloric
acids, sodium hydroxide, ammonia. Except for nitrous fumes from exposure
of nitric acid to air, or deliberate creation of aerosols through spray-
ing, most of these products are likely to produce only minor irritative
effects in their usual applications.
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In recent years the dose-response characteristics of many common
solvents have been undergoing reevaluation, using improved biological
monitoring techniques [649]. It has been found that measures of exhaled
breath concentration and metabolites in blood and urine have correlated
much better with biological response tests than air concentrations. These
investigations have led to establishment of standards on a firm metabolic
basis.
Stewart [610] has confirmed the metabolism of methylene chloride
to carbon monoxide and he has developed the correlation of ambient concen-
trations of CH2C12 with COHb levels in those exposed. Halse [265] indicated
that the Wisconsin group has now tested 10 solvents, and they and others
have found that only the dihalomethanes are CO converters. In testing the
usual standard levels with human volunteers, they have not identified any
factor which would indicate a need to change the recommendations for
acceptable concentrations.
8.6.2 Aerosol Propel1 ants
The three essential components of aerosol sprays are the pro-
pell ant, the solvent, and the active ingredient. Each might prove hazard-
ous to health. The most common propel!ants are fluorochlorohydrocarbons
bearing the trade name Freon'.* Freon 12, the most common of the group,
is a gas at room temperature, is relatively inert and has a high vapor
pressure that provides the propel1 ant force. We know little concerning
the range of exposure to aerosol sprays that might occur with their use
* Freon is a trademark of the E.I. DuPont de Nemours G Co.
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in relatively confined (indoor) space [219]. The use of these propellents
varies from hand nebulizers (i.e., by asthmatics), to hair sprays, to
other purposes.
Fluorocarbons in high concentrations have been reported to
affect both the respiratory and cardiovascular systems. Taylor and Harris
[623] noted that a mixture of Freon 12 and Freon 114 induced sinus brachy-
cardia and atroventricular block in experimental animals. The arrhythmias
were more readily elicited and more severe if anoxemia was present. Some
critics maintain that these effects are noted only when unrealistically
high concentrations of fluorocarbons and other substances are
combined [125]. Harris and Kilen [274] in further studies reported
that Freon 12 affected the contractility of myocardial muscle fibers.
An increase in mortality from asthma in children and young adults
in England and Wales during the last decade has been attributed to the
introduction of hand nebulizers [219]. One hypothesis is that the hypoxemia
(and hypercarboxemia) of the underlying asthma, in combination with the
inhaled fluorocarbon and adrenogenic drugs, led to fatal cardiac arrhythmias,
Trochinowitz et al. [623] found that industrial halocarbons posed no
greater risk in persons who had recovered from myocardial infarcts than
in normal individuals.
Morgan et al. [435] used radioactive tracer techniques to
study retention of Freon in human volunteers. Mean retentions of these
substances were:
Freon 11 - 23.0 percent (+ 2.2)
Freon 12 - 10.3 percent (± 2.2)
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t Freon 113 - 19.8 percent (± 0.9)
Freon 114 - 12.3 percent (± 4.1)
indicating that much of the vapor was exhaled without being absorbed.
After 30 minutes the fraction retained in the lungs ranged from 10 per-
cent for Freon 114 to 23 percent for Freon 11. Only a small fraction was
present in the blood at 5 minutes. The authors concluded that because of
low liquid solubility, absorption is quite slow and more than half the
material is exhaled immediately.
Foltz and Fuerst [216] conducted mutation studies with Drosophila
Melanogaster exposed to four fluorinated hydrocarbons. They found sig-
nificantly increased mutation rates in the F2 generation, including two
tumors not previously reported in deviant genotypes. The contribution
of anoxia to mutations was not determined. Vozovaya [672] used dich-
s
loroethane in mutagenic and hetrogenic studies of rats. Although
«!
concentrations did not produce observable toxicity, reduced fertility,
reduced birth-weight and an increased still-birth rate were detected.
Increased perinatal mortality was seen in second generation litters from
exposed males.
8.6.3 Pesticides
The term pesticide is used here in a generic manner and includes
the wide variety of chemicals used as insecticides, miticides, fungicides,
rodenticides, and herbicides. Many of these chemicals can be obtained in
a number of forms (powders, dusts, liquids) for application and used for
multiple purposes. Frequently they are combined in proprietary preparations.
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When considering the relative toxicity of each chemical, one must review
the following points:*
The lethal dose in animals
The method of use (solid, liquid spray, dust)
t The route of human absorption (ingestion, skin absorption,
inhalation)
0 The vehicle in which the pesticide is applied - the
diluent itself may be toxic or may influence the rate
of absorption
The formulation - many pesticides contain nonpesticide
ingredients which may enhance toxicity, combinations of
pesticides may act in synergistic or antagonistic fashion
relative to human toxicity.
The individual chemicals and combinations are far too numerous to discuss
separately here but important characteristics of each class can be
described.
The following summary of pertinent aspects for major classes of
pesticides is drawn from Hamilton and Hardy [266].
Organophosphorous Compounds - The mechanism of toxic action of
these compounds is based on their inactivation of acethylcholinesterase.
The natural substrate (AcCH) of this enzyme is a primary neurohumoral
transmitter substance. Because of certain structural similarities, the
Organophosphorous compounds undergo changes analogous to the natural sub-
strate. However, the bond to the enzyme is abnormally stable so that the
phosphorylated enzyme loses its normal function as a AcCH esterase, causing
* Occupational Health and Safety, International Labour Office, Geneva, Switzerland, 1972.
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first increased function and finally decreased function, with greater
AcCH accumulation.
The consequences are primarily disturbances of the central and
autonomic nervous systems. Systemic responses produce initial symptoms
such as anorexia, nausea and sweating. Eventually the respiratory muscles
may be impaired. Studies of workers with chronic exposures have shown
neurological deficits (memory defects, delayed reaction times) without
obvious clinical signs of intoxication.
There is wide variation in mammalian toxicity shown by this
group. Certain sulfur-substituted compounds require metabolic oxidation
before toxicity develops (e.g., parathion), while others (e.g., TEPP,
phosdrin, DDVP) do not require such modification and are direct inhibitors
of AcCH. The latter generally are more toxic and show more rapid onset of
s
systemic symptoms. Recent evidence [706] indicates that parathion and
related compounds are more toxic when inhaled than by skin absorption.
Also, the toxicity of parathion may be potentiated by ultraviolet and
visible irradiation.
Chlorinated Hydrocarbon Insecticides - The mechanism of action
in mammals or insects is not clearly understood. It is apparent that
these materials are neurological poisons, and severity of symptoms appears
to be directly related to the concentration in nervous tissues. Signs of
central nervous system stimulation from slight exposures include headache,
anorexia, nausea and irritability. Increasing exposure produces weakness
paresthesias, tremors and muscle fibrillation. Seizures or coma may occur
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after high levels of absorption. Long-term, low-level exposures produce
the clinical picture of acute response to intense single exposures after
sufficient dose.
Compounds in this category can be absorbed through ingestion,
through inhalation, and most through the skin. Dieldrin can be absorbed
through the skin in a dry state, the others must be in solution. There
are two particular health concerns with the chlorinated hydrocarbons.
First, the material absorbed is stored in fatty tissue. It has been
noted that the total amount stored in the fat of an experimental animal
may be greater than the amount necessary for a single fatal dose. Although
the stored material is probably biologically inactive, there is a question
of the potential danger from release of the pesticide during periods of
rapid weight loss. The second concern is the carcinogenetic potential of
these compounds. Those identified so far as possible human carcinogens
are aldrin, dieldrin and DDT. Because of these concerns, use of DDT has
been banned in the U.S. and others are being withdrawn or limited in appli-
cation. However, pesticides in the same chemical and toxicity categories
remain in common use.
Persistence of the chlorinated hydrocarbonr over time at effec-
tive levels aids their insecticide! properties but consequently poses a
health hazard. Davies and his associates [151] studied DDT concentrations
in an area where no aerial spraying had been done but where this insecti-
cide was used extensively for domestic pests. They concluded that con-
tamination of house dust was primarily responsible for the human serum
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residues found. Comparison of exterior soil and interior dust revealed
contrasts in concentrations of 8.4 ppm outdoors and 129.1 ppm inside.
Inhalation of contaminated house dust may be one important source
of uptake. Another source consists of the continuous vapors from sprayed
insecticides or from solid forms such as Shell's No-Pest Strip (DDVP).
Although the long-term consequences of such exposures have not been demon-
strated as adverse, many scientists feel that the use of these products is
imprudent. Although we have not obtained the detailed results, we understand
that Savage has recently shown that heavy application of chlordane and similar
chemicals for termite control can result in significant levels inside the
home five years after the spraying. Thus substantial indoor exposure does
not necessarily depend on direct household use of these pollutants.
Other Pesticide Compounds - The two categories described above
probably are the most important in terms of potential health consequences.
However, many other toxic compounds are in general use. Carbamates are grow-
ing more popular because of their effectiveness and relatively low order of
mamalian toxicity. These chemicals are also cholinesterase inhibitors
but the reaction is rapidly reversible when exposure ceases. Most aerosol
"bombs" for home use contain esters of the biological pyrethrum. Other
biological derivatives used are rotenone and nicotine. Pyrethrum and
rotenone may cause skin sensitivation but systemic intoxication is not
of concern. Nicotine however, is a potent neurotoxic agent which may be
absorbed from skin, lungs or GI tract.
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There are a considerable number of other chemicals which may be
of importance as indoor pollutants because of applications on foliage and
soil around indoor spaces. These include those for mites and other plant
pests, fungicides, soil fumigants, and herbicides. Among those of note
are:
Chiorbenzilate and Chlorbenside - These miticides resemble
the chlorinated hydrocarbons and have similar effects.
Dithiocarbomates - Foliage funqicidal sprays which may cause
eye and nasal irritation.but are not considered to have
important systemic toxicity.
Organomercury compounds - Aryl mercury compounds, the less
toxic of this group, are more likely to be used as
domestic fungicides. Mercury is a neurotoxic poison
and can cause active dermatitis.
Phthalimides - Frequently found in home garden fungicides,
they have not been shown to be a significant hazard.
Dinitrophengls - These are used in different formulations as
herbicides, fungicides, miticides and insecticides.
Action in man is based upon interference with temperature
control mechanisms. Members of this group used for
domestic applications are less toxic systemically but are
eye and airway irritants.
Chlorphenoxy group - This group includes the well-known
herbicides 2,4-D and 2,4,5-T. Skin absorption is
slight and toxicity by oral or inhalation routes has
not been a reported health problem.
t General statements in attempting to evaluate pesticides as an
indoor pollutant hazard are made difficult by the variety of formulations,
biological actions and toxicity levels associated with the many products
in use. Some of the aspects pertinent to exposure have been pointed out:
persistence in house dust, vaporization, transformation through oxidation
to a more toxic substance. To illustrate the diversity of pesticides,
Table 44 summarizes some relevant data on selected chemicals.
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TABLE 44. ILLUSTRATIVE SUMMARY INFORMATION ON SELECTED PESTICIDES
Compound
Oaaxatatotmovf
hrattdon
Aztopbos-methyl
(Cathtoa)
Hcalervos (ODVP,
VtnOM)
Itatstfckn
fikdiurtd Hydrocarbon
Utdue(BHC)
MibUn
Hstttchlor
wOttxyCeUof
Uttamatesi Carbaryl
iJSerta)
tebdcate Pyraduum
(HrmUa(
DHUocarbamatHi
Item
AS!*
Nttsehbisphenol
»t*«H>.CreO*>l
(DMOCJ
fifeUmidsE.
Sip*
Bunmetalsi
MkrlMtrwrr
faMe
UM
Plant pasa
10 percent aerosol,
S percent dint [278]
Household insects
A«io«olj, vaporixars
Plant pests, household
Insects
Solutions, dun
Household insects,
termites. Many
formulation*
Household insects
(limited) 0.5 parent
solution*, low percentage
dura
Household insects
Concentrates (24 percent),
2.5 percent data
HouMfaold Insect*
Many formulations .
Plant pest*
10 pareant data, SO
patcant liquid spray*
.Household iataca
Aerosols
Plant part*
Spray*
Intectldda, fungldde,
herbicide
Pecdddas, mngidde,
herbicide
Piutacllva fupgjdde
Fungidda
Plant pam
TIV
0. 1 mg/m3
(akin)
0. 2 mg/m3
(skin)
1.0 mg/m3
(kin)
10 mg/m3
(skin)
0. S mg/m3 .
(«kta)
0. 25 mg/m3
(sidn).
0.5 mg/m3
(«Wa)
10 mg/m3
(«Un)
Smg/m3
5 mg/m3
5 mg/m3
0.5 mg/m3
0.2 mg/m3
(tldn)
5 mg/m3
0.01 mg/m3
(tU»
0. 25 mg/m3 u
AS
Toxicity
LD$Q ntB oral 3-13 mg/kg,
dermal 6- 21 mg/kg [278]
LDso rao oral 11-13 mg/kg,
dermal 220 mg/kg [278]
LDso iats oial 56-80 mg/kg,
danaa! 75-107 mg/kg p78]
LDso me oml 1000-1375
mg/kg derail 4400 mg/
kg [278]
LDso «c oral 88-91 mg/kg,
dermal 900-1000 mg/kg
[278]
LDso r*6 oral 46 mg/kg,
dermal 60-90 mg/kg [278]
LDso <*6 oml 100~ 162 m8/
kg, dermal 195-250 mg/kg
[278]
LD$o i*c oral and dermal,
6000 mg/kg [278]
LDso >*e o1 850 B>g/kg,
dermal 4000 mg/kg [278]
LDso c °**^ ^" m*"'8
PJ]
LDso **tfl °**' 1300 mg/kg
P«I
Lathal I. V. dou in rtbbiot
22 me/kg [13]
LDso *«r 31 mg/kg [13]
LCsorao: orall2.5g/kg
[»]
10 mg/m3 lamal to mica
Expanse- Response Data
Procesrlng plane 0. 1-0. 8 mg/m3 decreased enzyme activity [13]
Inhalation tozidty greater man by ddn abnrpdon [13]
Aeroaoll (mitt, dust) highly haiardous [278]
1.7 mg/m3 air equivalent (m dietary Intake) produced no effect
In rets
Relatively low dermal toxicity probably accounts for good safety
record
0. 14-0.33 mg/m3 for 30 minutes/boor for 10 hourt over 14 days
produced no enzyme depreatlon [13] , 1 mg/m3 for 7-8 houn
produced 20-25 percent plasma enzyme depression [n]
84.8 mg/m3 1 hour {or 30 days produced no enzyme symptoms or
significant changes. Moderate itriatloa m nose and eyes [n]
Gammaisomer (Llndane) of BHC exhibits greatest toxicity but
relatively rapid excretion. Contact dermatitis reported from vapor.
Toxicity varies among spades [278] . 0. 19 mg/m3 continuous for
655 dayi with no effects in no. 0.7 mg/m3 average long-term
BHC produced symptoms in man at oral doses of Undane tolerated
for 14 days [l3]
Metabolite of aldrin wim similar characteristics. Undlssolved dieldrtn
readily absorbed through ddn, in con nut with DDT. Repeated
exposure has cumulative toxidty and residual toxicant- induced
Injury may artist [278 ] .Air dose established on basis of analogy to
Undane [U]
Action rlmllar to aldrine, chlordaae. Dermal toxidty to man esd-
matad 46 gm single dose, 1.2 gin/ day multiple exposure [13]
350 rag/ man/ day dietary dose over 2 yeaa produced no rymptoms,
700 mg/man/day produced no tissue daange,[13] .No Inhalation
data found
Dietary levels in rats of 225 mg/kg/ day without significant effect
[ 282] .Compound quickly metabolized. Inhalation of human equiva-
lent of 100 mg/day (10 mg/m3) in raa produced no gnat visible
injury. Mo skin notation for TLV [13]
16 mg/m3 per 30 minutes over 31 days produced only slight lung
irritation in raa, dogs. Mo skin notation for TLV [13]
Rats survived closed with estimated 500 mg/m3 for 4 hoots. Similar
effect* » antabuM, but more toxic. little experience data. No
skin notation for TLV [13]
Irritation of no«e at 0. 3 mg/m3 , marked irritation to nose and eyes
above 1 mg/m3. Skin absorption major factor in reported severe
affect! [13]
Human non- fatal intoxication above 2.5 mg/m3. Cumulative blood
levels and toxic effects after repeated exposure [13]
Low under acute toxidty but much higher chronic toxicity. 9000
mg/kg on lab animals caused slight tldn Irritation. Acceptable
daily intake for man estimated as 0, 1 mg/kg/ day. No sk»
notation for TLV [13]
0. 01-0. 1 mg/m3 with higher peaks did not reveal consistent
symptoms of Hg poisoning. However, current compounds considered
more toxlc,TLV Is 0. 05 for other non-alkyl Hg compounds [13]
TLV based in potential ASjO3 as dust contribution to arsenical
dermatitis. No inhalation data on AS in dusts or solution spray
[»]
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8.7 PARTICULATES
Particulates are a subset of the larger class of aerosols, an
aerosol being defined as a colloid system in which liquid or solid particles
are dispersed in a continuous gaseous medium. Aerosols are ubiquitous in
man's environment. They include primary participate matter (pollen, dust,
soot, fibers) emitted from natural or anthropogenic sources .and suspended
in ambient air, and they include secondary particulate matter (sulfates,
nitrates, some hydrocarbons) which are formed in the atmosphere by gaseous
reactions involving S0p» Nt^ and oxidants. Aerosols also include the
large class of diverse materials packaged under pressure to be dispersed
by a gaseous propellant (a class including deodorants, paints, hair sprays,
etc.). Particle sizes of aerosols range from that of aggregations of a few
molecules to visible dust and vapor.
The mix in these aerosols includes substances that are inert and
others that are biochemically and biologically active. The gas components
of aerosols range from those harmless to man in appreciable quantities to
those extremely hazardous in relatively small concentrations. These chemical
substances may not be detectable by any of the senses, may not produce signi-
ficant early physiological effects (to warn of their presence before serious
Injury) and may not produce clinically recognizable pathology until many
years after exposure. These facts, and the continuing introduction of new
materials in our environment from changing technology, make evaluation of
hazards extremely difficult and complex.
Brain and Valberg [79] have described'the results of studies on
respiratory aerosol retention, employing a model developed by a Task Group
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of the International Commission on Radiological Protection. Three distinct
physical mechanisms are Involved 1n deposition of particles: Inertia!
Impactlon, sedimentation, and Brownlan motion. The relative significance
of these mechanisms depends on the anatomy of the respiratory tract, the
effective aerodynamic diameters of the particles, and the pattern of breath-
Ing. The Important anatomic pulmonary changes, such as diminished lung
volume, are associated with aging and with various types of respiratory
disease. Particle aerodynamic characteristics are a function of particle
size, shape, and density. Breathing patterns change as a result of exer-
tion, existing pulmonary disease and various biochemical stimuli.
Clearance of Inspired substances 1s a complex process Including
direct expiration, transport by cilia and mucus to the pharynx where the
material 1s swallowed, and absorption Into the blood stream. Metabolism
and excretion from the blood, gastrointestinal and urinary tract are related
to the chemical properties of the Individual substances Involved. The
Inspired material may physically*or biochemically affect clearance mechanisms,
and metabolites may Induce pathology before clearance or be deposited in
body tissues where the potential for long-term action 1s realized. Results
from the model developed by the ICRP demonstrated that variations in
effective particle size and solubility can greatly alter retention and
exposure in some respiratory compartments [79].
Another recent study deserving citation here is an analysis of
trace element retention in the human respiratory system using proton-induced
X-ray emission techniques. Desaedeleer and Winchester [161] measured the
respiratory retention of lead halide and chalk dust sized by cascade impactor
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with stages ranging from 0.25-4 ytn. For both substances, minimum deposi-
tion was well under 50 percent with particles 1n the region of 0.5 )im
diameter, and deposition was well over 50 percent for both smaller and
larger particles. Retention results were consistent with those found
using the ICRP model and with those reported by other Investigators:
minimal retention of particles In a size range of about 0.3-1.0 pm, with
larger particles captured 1n the naso-pharynx compartment and smaller
particles lodging primarily 1n the pulmonary compartment.
The health hazards for several classes of particulates and other
aerosols are discussed below, grouped under the following headings:
Total suspended partlculates
Tobacco smoke
t Trace metals and minerals.
These categories do not embrace the whole range of possible
aerosols - biological pathogens and allergens have been excluded, for
Instance, because of time constraints In the literature review - and they
are not mutually exclusive categories. They have been selected as areas
of special Interest to researchers.
The organic compounds which enter the Indoor air as components
of aerosol sprays will not be discussed under this section. They appear
1n Section 8.6.
8.7.1 Total Suspended Particulates
The standard method of measuring the particulate content of out-
door air has been to weigh the total amount of particulate matter of all
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kinds retained on a filter paper through which ambient air has been forced
by a high volume air pump for a 24-hour period. The only characteristic
of the particulate matter so identified is its weight per unit volume of
air passed through the filter. The wide availability of these measure-
ments of total suspended particulate (TSP), usually expressed in terms
of 24-hour average ambtent concentrations in micrograms per cubic meter,
has led to the use of this measure of particulate concentration in epidemio-
logical studies. A cruder measure of TSP, the soiling index, has also been
used.
Sized analyses of ambient particulate matter, which separate
particles into size ranges, are available for research studies of the
smaller, respirable fractions of particulate. This type of particulate
analysis is not routinely available from air quality monitoring systems
s
established by states and cities. It is usually available only in special
research contexts, such as EPA's Community Health Air Monitoring Program
and other pollutant monitoring projects especially established for health
studies.
Total suspended ambient particulates as a group have been impli-
cated in a variety of pulmonary and extrapulmonary health effects. Their
presence and interaction with irritant gases were discussed earlier.
Figure 29 shows the data base for the National Ambient Air Quality Standards
criteria used by NAPCA [641]; it includes in parentheses the concomitant
concentrations of SOg found in these studies.
Cohen et al. [130] studied the incidence of asthma attacks
associated with pollution from a coal-fueled power plant. Sulfur dioxide,
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TSP
(SO, 715 /ig/m3, 24 hr) increase illness, excess deaths
700 f
600
500
400
300
(SO, 630/jg/m3, 24 hr) worsening symptoms bronchitis
200
(SO, 250 fjg/m3, 24 hr) increased absenteeism
{70% RH, small particles) reduced visibility
(SO, 120 fxg/m3, annual) increased respiratory disease
Direct sunlight reduced; (solfation 30 mg/cmVmo,
annual geometric)1 increased deaths likely
80 (Sulfation 30 mg/cm'/mo, annual geometric) increased
deaths possible
70 ~ (Other pollutants, annual geometric) public concern
60 ' (SO,, H,O, annual geometric) increased metal corrosion
Figure 29. Reference data for paniculate air quality criteria [607].
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soiling index, total suspended participates, suspended sulfates and sus-
pended nitrates were each found, by individual analysis, to explain a sig-
nificant variation in attack rate. However, (low) temperature and any one
of these pollutant measures, when taken together (multivariate analysis),
eliminated the significant contribution of the others. Temperature alone
appeared to be the most significant variable. It was concluded that tempera-
ture and pollutant concentrations had a greater relative effect when the
temperature was above freezing. This is consistent with the potentiation
of pollutant toxicity by higher-temperatures reported by a number of
investigators.
Sultz et al. [618] found a close association between the continuing
exposure to air pollution (defined by TSP level) and the severity of asthma
and eczema in children. Jacobs and Langdoc [328] reported an excess of
cardiovascular deaths among residents of a highly polluted industrial area
(with a variety of particulate pollutants), when compared with cleaner areas.
Lewis and Cough!in [388] studied the acid-insoluble soot contents
of male lung samples obtained at autopsy. A mean concentration of total
soot for both lungs of 1.7 g was estimated. A statistically significant
correlation was found between age and the quantity of soot accumulated,
but no association emerged when correction for occupational history and
smoking habits were made. Thirteen patients dying with mention of a
cerebrovascular accident had accumulated significantly greater quantities
of lung soot than the rest of the study population.
Stephenson exposed dogs to wood smoke for various lengths of
time [602] and studied the alteration in pulmonary function which occurred.
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The pulmonary dysfunction consisted of an early progressive increase in
the alveolar-arterial P02 gradient and a decrease in compliance. As
exposure was prolonged, the respiratory effects were followed by cardio-
vascular and neural dysfunction. In those animals which survived, the
authors noted a decreased resistance to bacterial infection. They did
not separate the effects of specific constituents of the smoke (heat, CO,
aldelydes, particulates).
As an indication of the hazard from TSP in indoor environments
it should be noted that TSP concentrations for one hour have been found
in indoor air as high as 462 yg/m3 [329] and 539 yg/m3 [241]. Elliot and
Rowe observed peak concentrations of 620 yg/m [185]. Penkala and de Oliveira
[485], among other investigators, have found that cigarette smoking will
increase indoor air TSP concentrations to above the NAAQS ambient standards
3
of 260 yg/m for a 24-hour average. Since the ambient air standard for
particulate is based in part on the health effects of particulate as measured
by high-volume samplers, comparisons of indoor particulate concentrations
with ambient standards should take into account the size and hence weight,
of particulate which enters these samplers. Since tobacco smoke particulate
is considerably smaller in size (approximately 1 ym mean aerodynamic cut
size) a significantly larger number of these smaller, and hence lighter
particles would be required to reach concentrations as high as the ambient
air standard. Further discussion of the health effects associated with
tobacco smoke appears in Section 8.7.2.
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In general, the data on suspended participates suggest that the
quantity, composition, size, and interaction of the particulates with pol-
lutant gases, must be taken into account when evaluating their health
hazards.
8.7.2 Tobacco Smoke
Tobacco smoke has been shown to increase the risk of cancer,
cardiovascular and other diseases, and to act in a synergistic manner with
other chemicals in carcinogenesis. These hazards have been extensively
studied from the point of view of their impact upon the smoker. The primary
interest in tobacco smoke in this literature review is, however, in its
impact as an indoor air pollutant affecting the health of the bystander.
Extensive reviews of tobacco smoke and its adverse affects on
human health have been provided by Kilburn [351] and by Schmeltz, Hoffman
and Wynder [546]. Kilburn points out that the pyrolysis of tobacco yields
over a thousand products, and she considers that the contents of tobacco
and smoke condensates are much too complex "to achieve the idea of relating
biological effects to single chemical components." Nevertheless, smoke
gases and particulates are of interest as composite pollutants, and indivi-
dual components may constitute a hazard in themselves if they reach sufficient
concentration from tobacco smoke alone, or in combination with multiple
sources.
Schmeltz [546] found no data suggesting that the passive inhalation
of tobacco smoke by non-smokers increases the risk of developing cancer.
However, his review cites three studies in which there was an increased
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incidence of acute respiratory ailments in children and infants, in homes
where the parents smoke. Griffin [253] notes that these studies are sus-
pect because of the statistical interference caused by increased respiratory
infections among the smokers themselves. However, Griffin cites a further
study in which parents' symptoms are controlled and the increased risk of
respiratory illness remains. Other effects cited by Schmeltz are eye
irritation and chronic respiratory symptoms (in persons particularly sensi-
tive to smoke), and elevated COHb and nicotine levels.
Tobacco smoke has the potential for causing a wide spectrum of
adverse health effects, since smoke contains carcinogens and cocarcinogens,
ciliotoxins and other agents implicated as contributing to an increased
incidence of cardiovascular disease and emphysema. Cigarette smoke has
been implicated as a source of cadmium in human tissue. Accidental exposure
to cadmium fumes can cause acute lung damage of the severe central-lobular
emphysema type. Hayes et al. [279] exposed rats to a polydispersed aerosol
of 0.005 in cadmium chloride for two hours. They noted a one-hour peak of
malate dehydrogenase activity (which may indicate specific mitochondria!
injury) and after two hours, type II cell proliferation and elevation of
glucose-6-phosphate dehydrogenase. They concluded that more than one mechanism
(effect) may be operating.
Most interest in tobacco smoke has been confined to CO as the
major hazard although more recently it is recognized as an indicator of
smokers pollution as well as a hazard in itself. Schmeltz cites a number
of studies which indicate that those more susceptible to oxygen deprivation,
such as cardiacs and anemics, may develop dangerously elevated COHb levels
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from passive Inhalation [546]. The controversy surrounding the hazards of
Indoor tobacco smoke concerns whether these persons should ever be exposed
to such concentrations, produced by others.
An important concern with tobacco smoke is the possible adverse
effects following chronic, low level exposure to tobacco's separate com-
ponents. Nicotine is the most prominent in terms of volume and has been
found in indoor air in concentrations as high as 10.3 yg/m3 (Section 4.0).
Others of particular interest are N02> the several existing nitrosamines,
and their possible conversion in the air or body to other known carcinogenic
nitrosamines.
8.7.3 Trace Metals and Minerals
The respiratory intake of lead has been of concern because of
widespread generation from automotive sources. ' Research relative to the
problem of atmospheric lead was reviewed by a committee of the National
Academy of Sciences [457]. They concluded that, at present ambient levels,
lead Inspiration did not represent a clear cut significant problem, but
that further research was required on acceptable body burden and the related
potential long-term effects.
The TLV established by The American Conference of Govern-
3
mental Hygienists for lead if ?00 yg/m [14], The work of Shapiro et al.
[562] gives some hint of the importance of lead as a pollutant in the urban
society. The authors examined the teeth from seven Egyptian mummies and
teeth from modern non-industrialized Indians from the Lacandon Forest in
Mexico. These two groups had similar and low concentrations of lead in
their teeth. A comparison with teeth from a modern, industrialized, U.S.
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population, revealed a 45 fold increase in the later group's dental lead
concentration.
Inspired lead is absorbed by the pulmonary bloodstream. The
degree of absorption is related in main to the proportion of lead dust
particles less than 5 pro in size and to the individual's minute volume.
Increased workload therefore results in higher lead absorption.* More
than 90 percent of the lead in the bloodstream will be held by the erythrocytes
but lead has a preference for bone and accumulates in bony tissue. Thus
the lead effects on the hemopoietic system include a decreased hemoglobin
content, a decreased number of erythrocytes and an increased number of
reticulocytes.
The chief early symptoms of lead poisoning are non-specific and
include diminished physical fitness, fatigue, sleep disturbance, headache,
aching bones and muscles, and digestive upset including anorexia. As
severity of poisoning ensues the disease will manifest itself in increased
signs and symptoms particularly involving the gastrointestinal tract and
the peripheral and central nervous systems.
Except in patients with anemia, the first clearly defined signs
of lead poisoning usually do not occur at a blood lead concentration lower
than 80 yg/lOOg of whole blood. However, certain chemical changes can be
demonstrated at levels below 40 yg/lOOg and possible subtle effects on
health and behavior are postulated. Two categories of people may be subject
to exceptional risk: workers exposed to unusually high ambient concentra-
tions associated with their employment, and infants and young children
exposed to lead in street dust. The latter group can probably ingest
* Occupational Health and Safety, International Labour Office, Geneva, Switzerland, 1972.
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and inspire sufficient lead to increase body burdens above a safe level.
On the basis of available epidemiological evidence, it was not possible
to attribute any increase in blood lead concentration to ambient lead air
pollution exposure below a mean concentration of about 2 or 3 yg/m - only
small groups of people have been identified as being exposed to higher
ambient concentrations than these. A special case of exposure, studied by
Bridbord and Shy [85] concerns the burning of candles with lead-core wicks.
3
Concentrations were observed to reach 20 yg/m in an indoor home environ-
ment.
Kopple et al. [358] have reported on a series of metabolic studies
designed to evaluate the relative contributions of inspired and dietary
lead to body burden. Using three techniques to calculate inspired lead,
intake when breathing normal urban air was estimated as high as 18 +_ 3 yg
.per day, suggesting that a person can incorporate a substantial quantity
of lead from inhalation of the ambient urban atmosphere. The authors
point out that despite the relationship shown with body burden usual ambient
lead levels have not been established as a health hazard.
Bogen et al. [75], in studying exposure of New York City residents
to lead, concluded that inhalation was the principal source of stable lead
intake. In a study of occupationally exposed persons, Johnson et al. [338]
found that lead and cadmium content of excreta, blood and hair were corre-
lated with airborne levels of these metals, but zinc, manganese and copper
were not. Angle and Mclntire [33] compared blood lead levels of urban and
suburban children of various ages. Urban children had higher levels, the
difference decreasing in the older age groups. No significant difference
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was found between urban and suburban sites in the lead content of air,
house dust, milk or water, or 1n available paint chips. Increased blood
lead levels for urban children were correlated with lead in urban dust fall,
yard soil and boot trays. Yard dirt and blood lead levels were associated
with residential proximity to traffic. Although all blood levels were
less than 40 »g, enzyme studies supported evidence for decreased red blood
cell survival at the levels found in urban children.
Excessive levels of aluminum from air conditioner deterioration
have been noted as a potential indoor hazard. Hamilton and Hardy [266],
1n reviewing studies on this metal, cite reported cases of interstitial
pneumonia, pulmonary flbrosis, severe aluminum pneumoconlosis, and emphysema
from Industrial exposures. Effects are apparently limited to respiratory
damage and severity 1s dependent on dose and particle size. Many of the
reports on the pulmumonary effects of aluminum are from the aluminum abra-
sives (AlgOg) Industry where a progressive, non-nodular interstitial fibrosls
(Shaver's Disease) has been noted among workers.* Since exposure in
all cases was not only to aluminum oxide but to silicon dioxide and to Iron
fumes, the role of aluminum as the etiologlc agent of Shaver's Disease
remains unclear. In the U.S., aluminum is considered non-toxic and regulated
o
as a nuisance dust, with exposure limitations of 15 mg/m . As Inhaled
aluminum reaching the lung appears to remain there, the effects of a cumu-
lative burden must be considered.
In reference to hazards from air conditioning it is interesting
to note, although biological contaminants have not been treated in this
review, the work of Banaszak [52] who reported four cases of a hypersensitive
* Occupational Health and Safety, International Labour Office, Geneva, Switzerland, 1972.
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pneumonltis among workers in the same office that was eventually traced to
contamination of the air conditioning system with a thermophilic actino-
mycete. Since that time four additional cases have been encountered,
three of which were verified as due to this group of agents in home air
conditioners or furnace humidifiers.
Many other toxic trace metals are found in urban air but do not
appear to obtain sufficient concentrations to be of concern, unless there
is an unusual local source. The use of platinum and palladium in auto-
motive catalytic converters has raised the question of their importance
in ambient air and studies are underway to assess concentrations, body
burden and toxicity [337, 305]. Hamilton and Hardy [266] indicate toxic
reactions to palladium were only produced in animals after injection and
there are no current reports of ill effects in workers. Platinum has
resulted in dermatitis and asthma in workers with occupational exposures.
Asbestos and talc have been associated with neoplasms in persons
exposed to occupational concentrations, and asbestos with nonoccupational
exposures [559],
Asbestos is a broad term embracing a number of fibrous mineral
silicates that differ in chemical composition. The three types of greatest
commercial importance are chrysotile, a hydrated magnesium silicate;
crocidolite, a sodium iron silicate; amosite, an iron magnesium silicate.
Chrysotile is the most widely used. The TLV of asbestos is 5 fibers longer
than 5 ym per mill niter [14].
The hazardous effects of exposure to asbestos of industrial
workers have been demonstrated repeatedly since the 1920's. The clinical
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consequences are generally considered to be of three types:
1. A potentially disabling pneumoconiosis characterized by a
"restrictive" pulmonary functional pattern with reduced total lung capacity,
lowered vital capacity without evidence of airway obstruction, reduced com-
pliance and Impaired transfer factor for carbon monoxide,*
2. Bronchogem'c carcinoma [558]. Enterline [191], in a discus-
sion of the methodologic difficulty of precisely relating exposure to asbestos
and carcinoma, states that while most agree there is an excess of the disease
in exposed persons, the magnitude of the excess related to exposure is not
clear. Many believe [565]* that there is a clearly greater risk of
cancer of the upper respiratory tract in asbestos workers who also smoke.
3. Mesothelioma, a diffuse carcinoma which invades the pleura
and sometimes the peritoneum.
As previously noted in Section 4.0, Nicholson [467] reported measure-
ments of asbestos fiber concentrations of between 100 and 5,000 yg/m in
the air of homes of asbestos workers. Additionally, 500 fibers/ml, were
observed 1n a building which uses a rotary asbestos heat exchanger. Other
Important potential sources of asbestos dust in the home are the use of insu-
lation and fire-proofing materials in standard.construction. Brake lining
wear also Introduces asbestos fibers into ambient air. Selikoff [558] cites
several reports which confirm the.deposition of these fibers in the lungs
of the general population; he and his colleagues examined relatives living
In homes of amosite asbestos workers and found asbestos-related pathology
in 38.6 percent of the first 210 persons studied. Selikoff reports that data
are now becoming available that will permit relating the degree of asbestos
exposure to lung burden.
Occupational Health and Safety, International Labour Office, Geneva, Switzerland, 1972.
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Occurrences of a nonoccupational risk from asbestos dust have been
reported from Britain and France; a few cases of mesothelioma have occurred
in persons who were living near a source of asbestos dust or who were exposed
at home, from dusty clothes brought back from work [631, 137].
An Important finding in the production of tumors by asbestos has
been made by Stanton [599]. Upon comparing the effects of various structural
forms of asbestos, fiberglass and aluminum oxide in rats, he found that
careinogenicity was related primarily to the fibrous structure rather than
to physiochemical properties. Fibers below 2.5 ym in diameter and 10-80 ym
in length were particularly carcinogenic.
Consumer talc products have been indicted as potential hazards
because of increased cancer risk among talc workers and because many talc
minerals contain asbestos fibers. Stanton [600] has reported the develop-
ment of an experimental mesothelioma with several varieties of fine fibrous
glass. Selikoff [558] concludes that while there is no convincing evidence
of cancer risk from inorganic dust (other than asbestos), there are still
too few studies on the potential risk, particularly at levels to which the
general population may be exposed.
8.8 AIR POLLUTION AND LUNG CANCER
The role of atmospheric pollution in primary cancer of the lung
is the subject of continuing controversy. One principal class of causal
agents of interest is the polynuclear aromatic hydrocarbons (PAH), many
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of which are known animal carcinogens. Evidence for the relation of PAH
'to lung cancer is based on their production of cancer in animals, their
presence in tobacco smoke, and the strong statistical association of
smoking with increased lung cancer in man. In addition to the argument
that this apparently logical sequence of observations does not constitute
unequivocal proof, the controversy stems from difficulty in separating
the individual contribution of more usual atmospheric pollutants from
those related to smoking and to occupational exposures.
Research on particulate polycyclic organic matter (POM) was sub-
jected to intensive review by a committee established by the National
Academy of Sciences [459]. It was concluded that there is an "urban
factor" in the pathogenesis of lung cancer in man and that benzo(a)pyrene
(BAP) could be used as an indicator molecule implying the presence of
polycyclic organic carcinogens. However, the NAS committee believed that
these substances had not been shown to be teratogenic, and the presence
of hydrocarbon mutagenesis and carcinogenesis had not been proven to be
closely related.
Carnow and Meier [107], in a statistical study relating BAP to
lung cancer in the U.S. and 19 other countries, estimated that an increase
of 1 ug/1000 m3 in concentration of BAP was associated with a 5 percent
increase in lung cancer mortality. (These data were used as the basis for
the Academy's recommendation for a working exposure-response hypothesis.)
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Hlrayama [297] has reported on a series of epidenriological
studies of lung cancer in Japan. In one prospective study the data
Indicated that the risk of lung cancer increases 10 fold if atmospheric
contamination is added to cigarette smoking. Sterling [602] published
a critical reassessment of smoking and lung cancer, suggesting that the
evidence was weaker than popularly, viewed and citing many studies which
-evaluated the important contribution of occupational and other atmospheric
pollutants. Subsequent rebuttals were made by Weis [683], Higgins [290],
and Bross [92]. Some of the material related to the discussion in these
papers concerned trends in respiratory cancer mortality reported by Higgins
[291].
The increased risk of lung cancer associated with cigarette
smoking 1s accepted by most of the scientific community, although the
particular constituents responsible have not been established. Polycyclic
aromatic hydrocarbons (including BAP) in the smoke are considered a pri-
mary candidate. These compounds are highly carcinogenic in animals and
recognized as a cause of occupational skin and cervical cancers [459].
Implication of PAH in Inhalation carcinogenesls has been reported for gas
workers and men working at coke ovens, and workers heavily exposed to
printing ink [459]. Most evidence for a role of other air pollutants in
lung and upper-respiratory cancer has also involved occupational exposures,
e.g., radon daughters, asbestos, haloethers, nickel, chromium. Although
the high exposure levels concerned would seem to make many of these factors
inapplicable to the nonihdustrial indoor environment, evidence is accumu-
lating on nonworkplace risk of respiratory cancer.
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Blat and Fraumeni [73] have reviewed data on arsenical air
pollution and lung cancer. They cite studies indicating an excessive
risk in smelter and pesticide workers. These data led to an analysis of
lung cancer mortality patterns in communities with arsenic-emitting
smelters which suggested an increased incidence of lung cancer in resi-
dents of these areas. Selikoff cites work of his own associates, and
others, which indicates significant asbestos levels and increased meso-
theliomas in families of asbestos workers and residents of areas near
asbestos industries [558].
The report of an association of respiratory cancer and sulfur
compounds by Winkelstein et al. [701] was discussed earlier. In this
regard, SO^ has been demonstrated as a co-factor in carcinogenesis with
BAP [458] and with arsenic (cited by Blat and Fraumeni [73]). This work
provides further evidence of the hazard posed by sulfur oxide-partial late
combinations.
8.9 SUSCEPTIBILITY OF POPULATION. SUBGROUPS TO. INDOOR AIR POLLUTION
Consideration of those population groups particularly susceptible
to pollutants requires that certain facts be borne in mind:
There is a wide variation in the susceptibility
of different persons to air pollution
Preexisting or underlying disease conditions
augment the stresses added by air pollution
Under some conditions, some types of air pollution
cause structural damage and persistent disease in
well persons.
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The primary population groups most effected by air pollutants
are those which have underlying disease of the organ systems involved in
the absorption, clearance and deposition of the polluting agent.
By far the most seriously affected population is that with pul-
monary disease - such as chronic obstructive pulmonary disease, bronchitis
or emphysema - since the most frequent route of absorption of air pollutants
is via the respiratory tract. This is evident from studies of the effects
of severe episodes of air pollution, such as that which occurred in London
in 1952 [429]. There was a dramatic increase in the mortality of those
with chronic lung disease at that time. Lawther [376] and Glasser [240]
have presented evidence that during less severe episodes of air pollution
(in London and New York) in many patients severe chronic respiratory
disease is aggravated. Individuals with pulmonary emphysema have some
degree of decreased dynamic compliance, increased airflow resistence,
ventilation/perfusion abnormalities, etc. Many of these patients often
have a reduced arterial oxygen saturation, usually with a concomitant
increase in PC02 [57]. Thus it is evident why their fragile physiologic
situation is adversely effected by air pollutants of various types such
as S0£, NOX, and CO.
Asthmatics are patients with a disease characterized by inter-
mittent bronchoconstriction and increased viscosity of bronchial mucus.
There is evidence that many common pollutants, including inert dust [173],
tobacco smoke and S02 [443] cause bronchoconstriction and thus tend to
aggravate the preexisting condition.
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Patients with low cardiac reserve due to chronic cardiovascular
disease, or with elevated COHb levels, can be jeopardized by high ambient
CO levels. Other groups, such as those with anemia or cirrhosis of the
liver, will suffer deleterious effects from agents which react with the
hemopoietic (CO) or hepatic (carbon tetrachloride) systems.
The older-aged population appears to be more susceptible to
the adverse effects of air pollution. The extent to which this phenomenon
is related to the increased incidence of cardio-pulmonary disease in this
age group, or to other factors related to the aging process and increased
infirmity, is not totally clear.
Douglas and Waller [167] followed 5,000 children from birth to
age 16 and studied the incidence of morbidity from respiratory disease.
They found a clear-cut association between an increased rate of lower
respiratory tract infection and the degree of air pollution in their envi-
ronment. Other studies for example, the work of Lunn et al. in Britain
[399], have confirmed this relationship. Children also seem more affected
by other pollutants, such as lead. To some degree this observation may
be related to absorption routes such as paint chip ingestion, less likely
to occur in adults. Although the factors in lead intake and balance are
not well established, children or workers who may already have a high
blood level could possibly achieve clinically important burdens from
respiration of ambient concentrations.
Further work appears warranted on the effects of air pollution
on those persons with preexisting depression, hypersensitivity states of
various types, and collagen disease [98].
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8.10 INTERACTIVE POLLUTANT EFFECTS
The interactive effects of combinations of pollutants have been
noted by many investigators and have been discussed in this literature
review in the reporting of research into the health effects of individual
pollutants. In summary it may be said that the synergistic action of
particulates and S02 seems to be well established. Some evidence is
available implying a similar action between particulates, N02» and oxi-
dants. Hackney et al. [259] found no significant differences in human
volunteers exposed to 03 and combinations of 03, N02, and CO, although
these experiments could not be considered adequate. The studies available
suggest an additive or synergistic effect on lung cancer of exposures to
POM from smoking, occupational pollutants, and ambient pollutants.
Several studies have investigated the contributions (individual
and in combination with pollutants) of temperature and humidity. The
CHESS studies and others have been cited which imply that the ambient
pollutants contribute more to aggravation of respiratory disease at
higher temperatures. PAN appears to be more potent at higher temperatures,
In a review by Green [249] of studies on the effects of indoor humidity,
it was concluded that increasing the relative humidity of occupied spaces
from 20 to 50 percent reduces the relative incidence of respiratory con-
ditions among school children.
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Burch [98] and Randolph [509] have been concerned with the
exposure to myriad chemical substances in the home. From his clinical
observations, Burch feels it is evident that home pollutants play a role
in autoimmune, collagen, and cardiovascular diseases. Randolph reviewed
the ecological basis for mental illness and describes a comprehensive
environmental control approach to managing mental problems. He presents
a lengthy case listing in which sensitivity to a wide variety of agents
in the patient's home was involved. Randolph describes the often subtle
progression to chronic symptoms. The extent of substances to which
hypersensitivity may occur is illustrated by cases reported by Randolph:
Gas appliances (many cases)
Hair spray
0 Perfumed toilet paper
Plastic furniture and curtains
Chlordane for termite control
0 Noise from electric appliance motors
0 Petroleum distillate for house dust control
0 Many pesticides, insecticides
0 Refrigerants (probably a Freon)
0 Foam rubber and hydrocarbon vapors
0 Textiles
0 Creosote, adhesives, bleaches, ammonia, mothballs,
and such miscellaneous household products.
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8.11 EVALUATION OF INDOOR AIR POLLUTANT HEALTH HAZARDS AND RESEARCH
PRIORITIES
One major objective of this study was to develop an overall
relative evaluation of specific indoor pollutant hazards, based on the
current state of knowledge, that would permit identification of research
priorities. The intent was to document a series of pollutant problems
that might be assigned degrees of importance in terms of potential
impact on human health considering the anticipated severity of effects,
scope of population concerned, feasibility of further definition, and
similar factors. In the abstract some definitive and comprehensive pur-
suit of this objective seems realizable but, as will be discussed, only a
partial resolution has been achieved here.
A methodology for a realistic ordering of the relative hazards
from the various identified air pollutants which may occur in indoor, non-
workplace environments will require at least the input 4nformation shown
in Table 45.
A ranking cannot be made without assigning numbers, however
crudely defined, to the elements being ranked. There are obviously gigantic
problems in obtaining numerical answers to the questions implied in Table 45.
Assuming for the moment that such numbers could be obtained - which may not
be a valid assumption - a model of an indoor air pollutant hazard rating
procedure might contain the elements and interrelationships for examination
of each identified indoor air pollutant which are shown in Figure 30.
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TABLE 45. ELEMENTS OF A POLLUTANT HAZARD RANKING METHODOLOGY
1. Identification of the full set of all the important air pollution-related adverse health responses, and
of the air pollutants associated with them.
«
2. Development of sets of exposure-response functions for each air pollutant (and for combinations of
pollutants) with the responses delineated as a graded series, of increasing severity for increasing
exposures, for various classes of the potential population at risk, such as:
normal healthy individuals
young children
elderly people
individuals with special respiratory, cardiovascular, or other health problems.
(This class will be divided into an appropriate number of subclasses.)
3. Development of criteria and a schedule ranking severity of response in terms of undesirability from
the point of view of society as a whole. Elements of this ranking might include:
level of disability (mild discomfort to death, in graded intervals)
duration of disability
time from exposure to onset of disability
value to society of affected individual (unless it is assumed, for example, that
chronic disability of a child, an economically active adult and a bed-ridden elderly
person are all of equal disbeneflt to society).
4. Estimation of the total numbers of people in the United States in each class and subclass defined in
Item 2.
5. Definition of graded sets of quantified air pollutant exposures, corresponding to the various graded sets
of response severities developed in Item 2. These sets of exposures must be expressed not only in terms
of total quantity of pollutant but also in terms of intensity and duration of time intervals between
exposure and response.
6. Mobility estimates for each class of the population identified in Items 2 and 4, defining the total
amount of time spent by the population of each class in nonworkplace indoor environments.
7. Determination for (each air pollutant and combination of all pollutants identified in Item 2) of a
graded series of indoor pollutant concentration levels, for short-term and long-term durations, which -
when multiplied by time spent in indoor environments by the average member of each population
class (see Item 6) - would result in the various graded sets of air pollutant exposures corresponding
to different severities of health response as defined in Item 5, (The indoor air pollutant concentra-
tions so defined would in effect be graded concentration hazard levels for indoor air pollutants and
as such could become the basis for indoor air quality regulations.)
8. Estimates of the frequency with which indoor concentrations of each air pollutant, and combinations
of pollutants; equal or exceed the various graded pollutant concentration levels (determined in
Item 7) in the totality of nonworkplace indoor environments in the United States.
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Frequency with which high
pollutant concentration levels
occur indoor* in the United States
(a number, less than one)
Expected high values of pollutant
concentration levels for short-term
and long-term averaging periods
(a quantity of pollutant)
Lengths of time spent by average
individuals of the various population
classes in indoor environments
(time periods)
Air pollutant exposures
for various population classes
(quantities of pollutant over time)
Health response
for various population classes
(ranked severities of response, from 1 to 10)
Ranking of societal values
(diibenefit ranking) of response severities
(a relative value, from 1 to 10)
Numbers of individuals in each
population class
(total numbers)
National indoor air
pollutant hazard indicator
(a number)
Figure 30. Elements of a pollutant hazard rating model.
The functions relating sequential elements of this model would
be complicated. In some boxes of the model there would be a need to develop
weighting factors; for example, if a pollutant occurs frequently at high
concentrations 1n one critical type of inhabited indoor environment but
almost not at all in other environments, it might be desirable to give it a
higher frequency credit than the absolute numbers of its national frequency
of occurrence would suggest.
A ranking of relative pollutant hazards in indoor environments
would be obtained by (1) performing the calculations implied in this model
for each pollutant and combination of pollutants specified earlier in
Item 2 of Table 45, and (2) comparing the resulting hazard indicator numbers.
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Having described a conceptual approach to the ranking of indoor
air pollutant hazards it is now necessary to say that in our opinion with
the current state-of-the-art no formal, logical ranking is possible. The
major reasons for this are:
0 The amounts and quality of data available to answer
the questions implied by Table 45 are highly variable.
The pollutant concentration characteristics of typical
indoor environments are only just beginning to be
explored. For some pollutants, such as carbon monoxide,
something is known about frequencies of occurrence and
indoor concentrations and much is known about exposure-
response functions for various population groups, but
for many other pollutants - such as respirable frac-
tions of particulates, and most of the orgam'cs - far
less is known.
It is not yet possible to forecast the long-term effects
(particularly in low concentrations) of many agents,
especially of those chemicals (such as those in pesti-
cides and aerosols) that have more recently come into
general use.
The ranking of health response severities in terms
of social values will be extremely difficult.
Criteria such as level of disability will be judg-
mental, even more so will be the weight given to
time before onset of disability. General accep-
tance of criteria for ranking severity of response
would be difficult to obtain.
The problem is also complicated by the consideration that
research priorities cannot be based solely upon present pollutant exposures,
but must anticipate trends. For example, shifts from low to relatively
high sulfur fuels in energy production, required to meet a larger portion
of national energy needs with domestic resources, may suggest a renewed
interest in S02 and sulfate pollution research which would not be engen-
dered solely by consideration of present needs for health effects research
in sulfur oxides vis-a-vis other potential indoor pollutants.
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We have now described (1) a conceptual approach to hazard rank-
ing of pollutants and (2) reasons why we are not prepared to pursue a
quantitative implementation of this approach. However, there remains a
need for the scienfitic community to make judgments about priorities of
research in the field of indoor air pollution. An effort is made in the
following paragraphs to make some provisional rankings, unsupported by
numerical analysis, which draw upon the principles outlined above and upon
the large body of research reviewed in this study.
In the most general sense, evaluation of indoor pollutant hazards
must encompass study of all ambient pollutants plus many of those that
occur in industrial processes. The scope of this perspective, when taken
with the sparse data on exposure levels and long-term effects, has led to
the conclusion that a chemical-by-chemical approach is beyond the capa-
bilities of this project. However, by focusing on unique aspects of
indoor pollution brought out in the review, and by applying some of the
principles of the formal approach without hard numbers, it is possible to
make broad, general recommendations on research priorities. These recom-
mendations consider the following factors for the several major classes
of indoor pollutants:
The size of the population exposed
0 The anticipated health impact at estimated
common indoor exposure levels
The unknown factors important for further study
0 The apparent advantages or difficulties for further
research suggested by the review.
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On this basis, and considering only those pollutants which have potential
for unique indoor concentrations, we would rank pollutant groups for
further investigation in the following order of decreasing priority.
1. Carbon Monoxide, Nitrogen Oxides, and Sulfur Oxides
These ambient gases (and the transformation products of N02
and $02) present a potential hazard to large populations, particularly
in urban areas. Substantial amounts of the gases may be generated from
indoor sources, primarily from the use of fossil fuels in cooking and
heating appliances. Carbon monoxide is also a major component of tobacco
smoke. These gases affect both the respiratory and cardiovascular systems
and therefore have a deleterious effect on two of the largest susceptible
population subgroups, those with clinical disease of these types. While
a great deal is known, significant questions remain, i.e., their syner-
gism with each other and with other agents and the relation of temperature
and humidity to their action.
2. Tobacco Smoke and Its Products
(In Addition to CO),
drocarbons (PAH),
Such as Pplynuclear Aromatic Hy
Cadmium, Nicotine, and Nitrosamines
Since a large proportion of the adult population continues to
smoke, particularly in the indoor milieu, many nonsmokers are also exposed.
In addition to its adverse effects on patients with cardio-respiratory
disease, cigarette smoke has been indicted as a causative agent in broncho-
genie carcinoma, and apparently is contraindicated in those with hyperten-
sion.
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The role of each specific byproduct of tobacco smoke is not well
understood, nor is its apparent synergism with other pollutants. Until
these questions and others are answered, the process of correcting its
toxicity, or of successful public education, will be difficult.
3. Pesticides: Chlorinated Hydrocarbons and Orqano-
phosphateT
The accelerated use of these agents over the past three decades,
has greatly increased the potential exposure in the indoor environment.
Many of these agents are widely dispersed in indoor spaces and tend to
persist for long periods of time. Further study, particularly of their
long-term human consequences, is warranted.
4. Trace Metals and Minerals. Particularly Lead. Cadmium,
Arsenic and Aluminum
The population exposed to these agents is large, particularly
to those arising from automotive exhausts (lead) and cigarette smoke
(cadmium). While other agents in this group (asbestos) cause severe
clinical disease in the human, they probably do not affect large numbers
of people. Much is yet to be learned regarding their long-term effects
in low concentrations.
During the initial stages of the literature review upon which
these recommendations are based it appeared that the rapidly increasing
use of fluorcarbon propel1 ants in indoor environments, coupled with the
lack of information about the possible health effects of repeated high
short-term exposures, would justify further study of the health hazard
of fluorcarbons in the indoor environment. However, action now being
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taken by the U.S. Food and Drug Administration (and by officials in other
countries) to phase out the use of fluorcarbon propel1 ants in consumer
products - largely because of potential damage to the ozone layer - has
probably mooted their problem.
It is apparent from our literature review that establishment of
the degree to which in fact, current or future indoor pollutant levels
pose a serious hazard to human health must await documentation of (1) the
actual exposure histories of various categories of persons and (2) demon-
stration that such individual and combination exposures overcome physio-
logical defense mechanisms to produce adverse effects. Many of the chemicals
reviewed have been given low priority because of the difficulty in identi-
fying adverse health effects from long-term, low-level exposures, and
#
because of the lack'of any convincing evidence that their presence as air
pollutants at the probably concentrations experienced would pose a health
hazard. This would include a wide variety of cleaning and hobby materials
that may be hazardous if normal precautions are not taken or if ingested
or subject to lengthy skin contact.
The selected ambient gases were given highest priority because
of documented indoor concentrations and documented adverse human responses
at those levels. It seems important, from an epidemiological view, to
now determine actual exposure and absorbed dose considering pollutant and
occupant behavior. The situation appears to offer several unique advant-
ages for study of health effects in that contrasting exposure conditions
within the same study community might be defined, based on combinations of
indoor and outdoor sources. This would take into account not only the
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factor that gas appliances may add appreciable quantities of pollutant
to the indoor spaces (and thus total exposure) but the converse hypothesis
that spaces with electric appliances and reduced outdoor infiltration (say,
because of air conditioning) may provide significant shelter from the more
reactive gases.
The remaining priorities were not as clear-cut. Tobacco smoke
seemed of importance .because of the variety of toxic agents, the amount of
pollution generated, the established long-term effects in smokers, and the
seemingly high potential for adverse effects in bystanders. The other
three groups are considered to be about of the same order of hazard. With
these latter agents it is important to determine the actual extent and
nature of exposure in indoor spaces before pursuing further health studies.
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Section 9.0
MODELING OF INDOOR AIR POLLUTION
An important purpose of indoor air pollution research is the
Improvement of ability to predict pollution impact and to propose actions
which reduce adverse impacts before such impacts occur. Research described
in earlier sections of this report has accumulated observations about
indoor air pollution, building energy and occupancy characteristics, and
the health effects of air pollution. Observation and measurement are
essential elements of an understanding of the indoor air pollution problem.
By themselves they are inadequate as guides for prediction and control of
indoor air pollution. For those purposes the observed facts must be
synthesized into predictive methodologies.
9.1 OBJECTIVES
Methods are needed for problem definition and for estimating the
probable environmental outcomes (indoor pollutant concentrations, energy
costs, pollutant exposures, and health effects) which may accompany measur-
able conditions (outdoor pollution, indoor pollutant sources, building
characteristics, and human activity) affecting the indoor environment. A
method through which a quantified, generalized definition of a complex
problem can become the basis for calculating presently unknown outcomes
as the simultaneous or subsequent concomitants of known or assumed initial
conditions is by definition a model. An important thrust of indoor air
pollution research is directed toward modeling.
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A planner who proposes to intervene In a specific indoor environ-
ment to Improve energy conservation, air quality or health will be concerned
with questions such as:
What energy conservation measures and results are
possible?
What levels of temperature and humidity may occur?
What air pollutants may occur indoors, at what con-
centrations, times and places?
0 What will be the durations and Intensities of human
exposure to these conditions?
What are the probable adverse health effects of such
exposures?
What Interventions are possible for the mitigation
of adverse impacts?
Which adverse health effects are the most undesirable;
I.e., what are the priorities for selecting alternative
outcomes and interventions?
What specific data must the planner have about present
and future conditions in order to make rational decisions
for Improvement of the indoor air environment?
t How sensitive are the outcomes of the predictive
methodology to Inaccuracies in the measurement or
assumption of initial conditions?
Questions of this kind can be addressed through modeling.
9.2 LIMITS OF CURRENT RESEARCH
There 1s a literature of scientific research in the modeling of
Indoor energy use and indoor air pollution. At least 16 building energy
models,. 3 building ventilation models and 5 indoor air pollution models
have been developed. Reports of these research efforts are described in
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detail in Appendix A of this report. The reader who wishes a detailed
mathematical treatment, particularly of the ventilation and air pollution
models, is referred to the Appendix. Table 46 provides a summary descrip-
tion of the five existing classes of indoor air pollution models, with
their inputs, outputs, and assumptions. Rather than report upon this spe-
cialized research in depth in the main body of the report, the presentation
which follows describes the general background and prinicples of indoor air
pollution modeling.
Models have been developed which describe indoor energy use and
ventilation in terms of building characteristics, meteorology and occupancy.
Modeling research in indoor air pollution has defined pollution concentra-
tions as functions of ventilation (and other enclosure characteristics),
initial pollution levels, and pollution decay. In a thumbnail sketch,
this is the state-of-the-art of indoor air pollution modeling.
Models do not yet exist for calculating human exposure to indoor
air pollution in typical, real environments, although efforts to develop
such models are currently being planned in the EPA Health Effects Research
Laboratories.
Models to describe changes in human health status as functions
of indoor air pollution (an even further step) would need to consider not
only indoor pollutant exposures but also the exposure history of each indi-
vidual to outdoor and workplace air pollution as well as many other aspects
of the individual's health and environmental history. The complexities of
this problem are beyond the capability of integrated modeling efforts at
this time. A workable outdoor-indoor air pollution human exposure model,
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TABLE 46. INDOOR AIR POLLUTION MODELS - INPUTS - OUTPUTS - ASSUMPTIONS
Model
(Generic Name)
Input Requirements
Model Outputs
Assumptions
References
Effective Residence
Time
Volume of structure rate of entry
(egress) initial concentration of
pollutant
Indoor pollutant con-
centration time
history
Instantaneous pollutant generation, ambient air
pollutant free, no sinks, no forced ventilation
system (1. e., one structure "breathing" rate
including both ventilation and infiltration)
G.H. Milly 1953 [426]
Constance 1970[l38j
Drivasetal. 1972 [ 171]
and others
Dosage Model
Interior Volume, filter efficiency,
air intake/exhaust rate, removal
rate, indoor source strength,
ambient concentration
Indoor pollutant con-
centrations in a
specified time
Constant indoor or ambient pollutant concentration
over a predetermined time interval is assumed in
the definition of dosage
K.L. Calder 1961 [102 ]
Milly and Thayer,
1967 [428 ]
il
CO
CO
IO
I
The "Well-Mixed"
Tank Model
Chamber volume, initial pollu-
tant concentration, source
strength, ambient concentration,
number of air changes, mixing
factor
Concentration of
pollutant in the
chamber at any
time
Perfect mixing is assumed in the chamber; nine
theoretical cases are analyzed, each one involves
a different assumption
A. Turk 1963 [634J
The "Black Box"
Model
Volume, ambient concentration,
volumetric rate of intake/
exhaust system, indoor source
strengths, rate of air recircula-
tion
Rate of change of
total concentration of
the pollutant in the
enclosed volume
Model applicable only on structures with forced
ventilation system and positive indoor pressure,
no infiltration/exfiltration terms, no sink terms
HuntetaL, 197l[318]
Hunt and Burch 1975 [317 ]
The Linear-Dynamic
Model
Indoor volume, filter efficiency,
indoor surface area, indoor source
strengths, outdoor concentrations,
infiltration/exfiltration rates,
intake/exhaust rate, recirculation
rate
Indoor pollutant con-
centration as a func-
tion of time
A first order decomposition mechanism for ozone
is the only sink mechanism considered
Shair and Heitner 1974 [ 561]
-------
used in conjunction with epidemic!ogical studies of human populations, might
represent the greatest extent to which simulation modeling can be applied to
the indoor air pollution health effects problem in the near future.
This report is intended as an assessment of the state-of-the-art
of current research. The discussion which follows is therefore limited to
what is presently possible; the predictive modeling of indoor air pollution
concentrations.
9.3 ELEMENTS OF INDOOR AIR POLLUTION MODELING
Indoor air pollution models simulate the changes in air pollution
concentrations over time in an enclosed space as a function of three basic
variables:
t Ambient (outdoor) air pollutant concentrations
0 Indoor air pollutant sources and sinks
Indoor-outdoor air exchange rates.
The basic variables are in part functions of other variables:
meteorology, ambient air pollutant sources, enclosure design (location,
size, materials, openings, construction techniques); heating, ventilation,
air conditioning (HVAC) characteristics; special energy conservation mea-
sures; indoor temperature and humidity; and enclosure occupancy character-
istics. These secondary variables are to some extent interdependent. A
diagram in Figure 31 illustrates some of these relationships.
Figure 31 suggests the complexity of the conditions an indoor
pollution model must simulate. The ultimate question the model answers Is:
What indoor pollutant concentrations will occur? In the process of
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answering that question the model must examine such questions, among
others, as:
1. To what extent are elevated indoor pollutant
concentrations due to ambient pollutants and
to what extent to indoor-generated pollutants?
2. To what extent are indoor pollution levels
reduced by pollution reducing devices?
3. To what extent are indoor pollution levels
affected by energy conservation measures?
The operation of an indoor air pollution model may also provide
Information (through linkage of occupancy and indoor pollutant concentration
data) which defines indoor pollution exposures for occupants of indoor spaces,
although a practicable integrated model structured to do this has not been
described in the scientific literature.
Indoor/Outdoor Air
Exchange Kau<
Figure 31. Major functional relations in indoor air pollution modeling.
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The primary output of an indoor air pollution model, pollutant
concentrations, can also be obtained by direct field measurements in the
environment of interest. The approach is practicable only in a research
context. Field measurements are expensive, and they must be conducted
over extended periods of time to assure results which reflect a full range
of possible input conditions. If the use of the indoor pollution concentra-
tion data is to generate personal pollutant exposure information for
epidemlological studies of large populations (a use contemplated in several
future studies now being considered by the Environmental Protection Agency)
It becomes Impractical, for reasons of cost and available measurement
technology, to plan for direct measurement of pollutant concentrations and
exposures for the large numbers of enclosures and people Involved. Model-
ing becomes, in such a case, an essential instrument because only it can
provide the necessary answers in a cost-effective approach.
9.4 THE MODELING PROCESS
Indoor air pollution models, as with other models, are likely
to be developed in a cyclical approach. Development begins with the
definition of candidate input and output parameters, and of such para-
metric relationships as are known or may be postulated. This is usually
followed by the performance of field monitoring studies of inputs and
outputs to provide data for the development of a numerical model. These
field data help to further define the structure and relationships of the
model, which must then be tested against more field data. The goal is
eventually to formulate a model which can simulate a large variety of
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conditions. A general indoor pollution model of such broad power has
not yet been formulated. As described in Appendix A, a number of models
of limited capacity and varying complexity have been constructed. The
fundamental principles involved in these models, their assumptions, the
approximations involved, and their constraints are outlined in what
follows. Appendix A contains the mathematical expressions involved in
each model and provides details which will probably be of interest only
to modelers. Readers who do not- expect to work with details of the
modeling process should find sufficient the material included in this
section; for them Appendix A is not obligatory reading.
Air pollution in an enclosure may be of outdoor or indoor
origin. If of outdoor origin it enters through infiltration and ven-
tilation. If of indoor origin it is generated from pollutant sources
within the enclosure. Regardless of source, air pollutants diffuse in
the enclosure. They are removed over varying periods of time by exfil-
tration and ventilation to the outdoors and through indoor decay. The
making of these simple statements marks the beginning of a conceptual
model. These concepts are further discussed below.
Air infiltration is defined as the change of air within a struc-
ture without the interference of the inhabitants. Thus the ambient air
entering an enclosure through cracks in its walls is infiltrated air which,
whether clean or contaminated, influences the indoor pollution levels.
Ambient pollutants may also be introduced indoors through the ventilation
process, which, may be defined as air change induced by the occupants of
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an enclosure; this can be natural ventilation through closing and opening
of doors and windows, or can be forced ventilation through the operation
of attic fans, air conditioning or heating systems. Air exfiltration is
the opposite of air infiltration, in which indoor air leaves an enclosure
through structural cracks. Exhaust ventilation moves air from indoors to
outdoors through the vents of a forced system as well as through door and
window openings. Indoor generation sources such as fireplaces, stoves,
smoking, cleaning devices and others introduce pollutants Into the indoor
environment. Finally, pollutants may be removed from the indoor air envi-
ronment through indoor decay processes such as chemical transformation,
settling, and absorption and adsorption by walls and furnishings (collec-
tively termed pollutant sinks), and by filtering procedures in the make-up
air or in the recirculated air.
Three elements are common in all existing indoor pollution
models; (1) the mass balance principle is the basis for the model; (2) per-
fect mixing of pD lutants is assumed within the enclosure; that is, no indoor
pollutant concer ation gradient is assumed in each model; and (3) prior
knowledge of all air exchange coefficients is required as an input for
modeling operations.
To characterize time-dependent aspects of pollutant behavior it
is useful to deal with rates of change of air pollution within enclosures,
rather than simply with absolute amounts of pollution. Mass balance
principles require that the rate of change of the quantity of an air pollu-
tant within an enclosure must equal the sum of the rates of all processes
of pollutant introduction and pollutant removal which operate upon the
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enclosure. This statement can be expanded into a differential equation -
the basic equation of indoor air pollution modeling - which is expressed
in words as follows:
The rate of change
of total indoor
pollutant quantity
equals
The rate of entrance of
pollutant in ambient air
through ventilation (with
or without air cleaning)
plus
The rate of entrance of
pollutant in ambient air
through infiltration
(without air cleaning)
plus
The rate of indoor genera-
tion of pollutant
minus
The rate at which pollutant
exits through exhaust venti-
lation of indoor air
minus
The rate at which pollutant
exits through exfiltration
of indoor air
minus
The rate at which pollutant
is removed by air cleaning
devices in recirculated air
minus
The rate at which pollutant
is removed from air within
the enclosure by indoor sinks
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Each of the verbal elements of this statement can now become a mathemati-
cal element in an equation. The mathematical expressions of this differ-
ential equation are not very complex (see, for examples, Equations 55 and
64 in Appendix A), but they involve a series of constants which must be
known before solutions of the equation can be undertaken.
A schematic representation of the way in which the terms of this
equation act upon a generalized building (or other enclosure) appears in
Figure 32.
Air Cleaning
Dcric*
Ventilation Ait tnd II Ambient Pollutant
Infiltration Air and
AmUat Pollutant
Eacloiurt Walb
Indoor Pollutant Some*
Indoor Pollutant Slnlo
RecircnUted Air and
Pollutant After Cleaning
Exfibration Alt ai
Exiting Pollutant
VeattUtioa Ate
and Exiting Pollutant
Figure 32. Schematic representation of indoor pollution model equation.
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9.5 MODEL PARAMETERS
Determination of values of the parameters involved in the model-
ing equation (i.e., providing numerical bases for the use of the equation
in actual calculation of pollutant concentrations) presents varying degrees
of difficulty. There are two principal categories of such parameters,
those concerned with structural characteristics of the enclosure and those
concerned with pollutant characteristics.
9.5.1 Structural Characteristics
Problems associated with estimating structure coefficients and
their constraints upon pollutant behavior (they influence air exchange
rates and thus influence pollutant behavior) have often been bypassed in
research contexts by limiting modeling application to a single, well-studied
structure, or by investigating a very specific problem or a single well-
understood pollutant. But the problems of determining equation constants
are very significant for the development of general models.
i
The forced ventilation rate can be calculated from the operational
characteristics of the heating, ventilating and air conditioning systems.
Natural ventilation rates can be calculated in terms of enclosure size and
openings, wind speeds and temperature differentials, as can infiltration
and exfiltration rates (although with less assurance). The ways in which
human behavior influences ventilation rates (through opening and closing
of windows and doors, and adjustment of HVAC systems) have not been quan-
tified for use in existing indoor air pollution models. Filter (air
cleaner) efficiencies enter into some, but not all, of the existing models.
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Filter factors may characterize pollutant removal make-up air and in
recirculated air. Extensive studies on efficiency of filters have been
undertaken in the past and there is available literature which indicates
how the efficiency varies with time for a large number of filters and
pollutants. This has been described in Section 7.0 of this report.
Determination of the infiltration rate, which is conventionally
assumed in indoor pollution modeling to be equal to exfiltration rate,
can be made experimentally in an enclosure through measurements of the
rate of reduction of the concentration of an inert gas released in the
enclosure. This is a simple process if infiltration rates are required
for only a small number of enclosures. But each house or other dwelling
will have its own infiltration rates, and direct measurement of all these
becomes impractical if large numbers or relatively diverse buildings are
to be modeled. In this case an information matrix relating structural
variables to probable infiltration rates must be developed to provide the
infiltration rate constants; this has not yet been done in research
reported in the literature.
9.5.2 Pollutant Characteristics
The rates at which pollutants are generated within enclosures,
and at which they decay, are not well documented. Previous research has
described indoor source strengths for combustion-related pollutants such
as carbon monoxide and nitrogen oxides; and emissions of pollutants from
cigarette smoking and some aerosol spray products have been measured (see
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Section 3.0 of this report for examples of available indoor source
strength research). Hard data are not available on indoor source strengths
of many indoor pollutants.
The least understood term in the indoor pollution model equation
is the indoor sink strength. It has been suggested by Dr. Fredrick H. Shair
(in a personal communication to the authors in 1976) that for pollutants
of low reactivity the sink strength is of secondary importance and that it
may be approximated to zero because other processes, particularly air
exchange rates, are dominant. Studies of decay rates for sulfur oxides,
carbon monoxides, particulates, nitrogen oxides, oxidants, hydrocarbons,
and trace metals have been reported in the literature (see Section 4.0 of
this report) but the selection of rate constants for specific modeling
contexts based upon this research still presents practical difficulties.
Despite the difficulties suggested above, numerical simulation
modeling of indoor air pollution promises to be a valuable, cost-effective
tool for investigating the causes and impacts of indoor air pollution and -
by extension - the health hazards of indoor air pollution.
9.6 CONCLUSIONS
At the minimum, an indoor air pollution model must provide a
framework within which it is possible to estimate pollutant concentra-
tions indoors in terms of specifications of corresponding pollutant
characteristics immediately outside an enclosed space, and the structural
and energy data of the building. It is highly preferable that such a
model have broader capabilities, particularly the ability to describe
indoor sources and behavior of pollutants. The reviewed indoor air pollution
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models presently achieve the minimum requirement for a given structure;
further research is needed to generalize the application of the models
and to extend their capabilities.
The following conclusions can be drawn from the study of
existing indoor air pollution modeling research:
The fundamental principle involved is straight-
forward (a mass balance equation), and theoreti-
cally sound. It has been used by all researchers
who have developed indoor-outdoor ventilation
and air pollution models.
t All practical applications of the existing models
require prior knowledge of a rather large number
of coefficients and constants included in the model
expressions. Extensive field work is necessary to
obtain these necessary factors.
There are many knowledge gaps. Internal pollution
generation and indoor source strengths must be
studied more extensively. Indoor sinks (decay rates)
need more attention. Indoor pollution levels are
affected by energy conservation measurements, by
inhabitants; activity factors, by home structural
characteristics and others; these relations are
inadequately known at present.
The most difficult research problem identified in this appraisal
of the literature of indoor air pollution modeling is in the determination
of the constants of the basic functional relationships involved in defining
t
structural effects in simulating indoor-outdoor air pollution levels. The
reviewed models have generally bypassed this difficulty by considering
only one investigated structure, and by experimentally determining the
required coefficients for that unique structure. An objective of any
new modeling effort should be to formulate a model that may be applied to
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any given building under varying conditions. . The following parameters
should be studied and should be connected in model form by functional
or associative numerical relationships:
Outdoor pollution levels
Indoor generation of pollutants
Building permeability (ventilation, infiltration rates)
Meteorological conditions
Ventilation system capacity
Building identification parameters, including zones
Energy conservation factors
t Indoor pollutant behavior
Human activity factors
t Indoor air pollution control devices.
A model capable of interrelating these factors, using data
readily obtainable by state-of-the-art monitoring and field survey tech-
nology, and fitted with coefficients of general applicability, would
represent a very substantial and important advance over existing model-
ing capabilities.
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Appendix A
MODELING OF INDOOR AIR POLLUTION
-A.I BACKGROUND FOR INDOOR AIR POLLUTION MODELING EFFORTS
Hazards to human health can result from the occurrence, behavior
and impact of air pollution, including, of course, that occurring indoors.
The hazard levels vary in a complex, not well-understood manner, in which
the kinds of pollutants, their concentrations and dosages, and their syner-
gisms with other pollutants and other conditions affecting humans play a
part.
Two important objectives in studying indoor air pollution are
(1) to obtain a better understanding of the potential health hazards involved
and the circumstances which create those hazards, and (2) to obtain infor-
mation upon which methods for controlling indoor air pollution - thus miti-
gating adverse health effects - can be based. The achievement of these
objectives requires the development of models which can describe and account
for the observed changes in the parameters of the interactions of indoor air
pollution with individuals and with the indoor environment.
Such models may be simple, qualitative descriptions of interactions
between a few elements of the indoor air pollution problem; or they may be
complex, mathematical descriptions, involving many parameters. All models,
to be useful in understanding the problem, have two common attributes: they
simplify complex situations by imposing a pattern and a limited number of
categories upon a set of facts, and they have a predictive capability. With
a model one can say that given a defined set of circumstances (inputs) there
can be calculated one or more other associated circumstances (outputs).
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A complete mathematical model of the indoor air pollution problem
would enable a researcher, given appropriate input information about air
pollution sources and other factors, to calculate health hazards in any
indoor environment. Some of the input data for that model would be extremely
difficult to obtain. With the present inadequate state of knowledge of
factors affecting indoor air pollution and human health the model's results
would be of doubtful validity. The complexity of the model, even with much
necessary simplification, would probably make it costly to operate. But
despite these problems researchers have considered it desirable to move
toward developing such models. Models represent an important key to under-
standing and correcting the problems of indoor air pollution, as described
in Section 9.0 of the main text of this report.
A model with an output which quantifies the health hazard (or
health effect) of one or more air pollutants in an indoor, nonworkplace
environment should:have the following major classes of inputs:
Ambient outdoor air pollution
Climatology and meteorology
a Building design and siting elements
Heating, ventilation and air conditioning characteristics
of the building
Indoor air pollutant sources
Indoor-outdoor energy flow
Building occupancy characteristics, including personal
habits of the occupants
Mobility patterns of the occupants within the building
over time
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Personal health status characteristics of the occupants
Toxiclty of the pollutants, in terms of dose-response
Exposure and dosages of air pollutants experienced by the
occupants when away from the building
Costs associated with all parameters.
No such general model exists, although several efforts to design
Indoor pollution exposure models, having much of this input, are now in the
planning stages. A large model of this kind, when created, will operate
through the joining together of less ambitious models which seek to describe
and quantify subsets of the major elements.
There is an important existing body of research in the modeling
of a subset of the first five factors listed above (ambient outdoor air
pollution, meteorological parameters, building design parameters, the
building heating and ventilation system, and indoor pollution sources) to
produce information about Indoor pollution concentrations. These models
are called "Indoor-outdoor" models. Five such models, of increasing
complexity are discussed subsequently. The simplest of these endeavor
only to describe and quantify Indoor-outdoor air exchange rates, but such
quantification 1s an essential element of any effort to relate Indoor to
outdoor air pollution concentration levels.
The recent emergence of a new concern 1n the United States for
energy conservation has led to an increased interest 1n reducing energy
losses from buildings, and in creating new building design standards which
reduce the rate of Indoor-outdoor air exchange in buildings - thus retaining
heated or cooled air within the building and minimizing energy loss. The
indoor-outdoor relation of air pollutants are also altered by these measures.
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Models which endeavor to define energy flow-air exchange-structure-
meteorology relationships in buildings are thus also of potential interest
and use in defining indoor-outdoor air pollution relationships and indoor
air pollution levels. Such models are also discussed in the text which
follows.
In summary, it can be observed that indoor air pollution models -
either in their ultimate full form of exposure-dosage-response models or in
the limited form of indoor-outdoor air pollution concentration models -
may be valuable tools for the health planner, the building designer and the
air quality planner. These models can assist the planner to decide where
and in what quantitative manner he should intervene in the indoor air
pollution problem to limit the adverse health effects of indoor air
pollution while optimizing energy conservation and costs.
Against this background the present report reviews the literature
of analytical modeling studies of indoor-outdoor air pollution relationships.
Specifically examined is the state of the art of definition of the following
model parameters: pollutant source strengths, decay rates, indoor environmental
parameters, structure identification parameters, and the impact of human
activity. Following the review of the state of the art, as exemplified by
descriptions of modeling work of previous researchers, there is a discussion
of the elements of a new model development program which is now underway at
6EOMET.
A cautionary note is in order. The discussions which follow are
not solely a literature review. To some extent they are also expository,
endeavoring to set out basic principles of air flow and modeling, leading
to the description of some new concepts for indoor-outdoor air pollution
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modeling. The text is at times quite detailed, presenting mathematical
descriptions which will probably be of Interest only to modelers. This
material 1s Included for Us value to those who will work 1n the future upon
the Improvement of existing models. Readers who do not expect to work
with details of the modeling process will find this material of lesser
Interest; for them 1t 1s surely not obligatory reading.
A.2 SIMULATION MODELS
This section 1s divided Into three segments: the first segment
provides a brief summary of models and computer programs available for
calculating energy loads and consumption; the second segment reviews
numerical simulation of Infiltration and Indoor air movement; and the
third segment reviews five models which relate Indoor-outdoor air pollution
levels. The energy consumption models do not directly address the relations
between Indoor air pollution and energy conservation, but they do speak to
the. general question of relating energy consumption measurements to
ventilation and Infiltration rates and to Indoor-outdoor meteorology. The
discussion of numerical simulation of Infiltration and Indoor air movement
1s relevant as an Introduction to the problem of Indoor-outdoor pollution
i
modeling, which is addressed in the third segment.
A.2.1 Energy Load and Consumption Models
There are numerous computer programs available for calculating
energy loads and consumption for the heating, ventilating, and air condi-
tioning of buildings. These energy models differ widely in methodology,
input requirements, and resulting output form. Table A-l, on the eight fol-
lowing pages, includes brief descriptions of some of these programs which
contain either a detailed load analysis program or a comprehensive system
simulation program.
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TABLE A-l. ENERGY MODELS - METHODOLOGY - INPUTS - OUTPUTS
Model
(Code Name)
Input
Requirements
Model
Outputs
Date-Status
Developer
Descriptive Comments
A PEC Heating -
Cooling Calcula-
tion Program.
Version III (HCC)
Building description,
weather data, solar
radiation data,zone/
room description and
systems description.
Room loads and cfm values,
zone loads and cfm values,
system analysis results,
building peak refrigeration
and heating load. Optional
output for cooling load
analysis for 12 hours of a
design day.
Completed 1972,
revised 1973.
Automated Pro-
cedures for Engi-
neering Consultants
(A PEC),
Dayton, Ohio
CO
en
I
The program calculates design heating and
cooling load utilizing ASHRAE methodology.
The room is the basic level of calculation
for which the requisite design data is speci-
fied. Heating load calculations consist of
conventional transmission loss analyses
involving areas, U factors, and temperature
differences. Infiltration is calculated on an
input or master factor basis. The maximum
glass solar heat gain for the specified winter
month is calculated and its effect on the heat
loss for the room is determined along with
lighting and occupant heat gain. Cooling load
calculations are made on an hourly basis over
a 24-hour period for the selected design day,
and radiant load components are time-averaged
in accordance with the building mass. Glass
loads are separated into transmission and solar
components, taking into account the glazing
material and shading devices. Hourly room
loads and cfm values are accumulated and
analyzed psycrometrically and peak loads on
equipment are determined.
Computer language: Fortran IV.
Building Load
Estimating Soft-
ware System
(BLESS)
Summer and winter
design conditions,
building design
parameters, room
exposure data, room
data, glass, wall,
and roof types.
For the entire building and
each room: month and hour
of peak cooling and the
cooling load cfm, and air
changes at this hour. Winter
heating load for each room.
Operating;
V. C. Thomas,
Daverman Ass.,Inc.
Crand Rapids,
Michigan
The conversational type program calculates
cooling loads for each hour for every summer
month and the heating load at the winter design
condition. The method of calculation used is
described in the Carrier Air Conditioning
Design Manual. The conversational mode
enables the user to correct input errors as they
occur and to vary input parameters repeatedly
to suit the requirements.
Fortran IV is used.
(Continued)
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TABLE A-l. ENERGY MODELS - METHODOLOGY - INPUTS - OUTPUTS (Continued)
Model
(Code Name)
Input
Requirements
Model
Outputs
Date-Status
Developer
Descriptive Comments
Deere and Co.
Load Calculation
Program (AIRCON)
Input follows require-
ments of "Carrier Load
Estimating Guide."Also
needed: lighting sched-
ule, sensible load
schedule, occupancy,
coil position relative
to fan, ceiling return
air plenum.
Output follows format of
Carrier Load Estimating
Sheet; additionally it
includes temperature list-
return air, mixed air, entering
and leaving coil, leaving fan,
apparatus dew point, air
changes per hour, CFMDH
per ton, square feet of floor
space per ton, percent outside
air, time-load profile, heat
loss estimate.
'Operating;
B.Davis Deere and
Company
Moline, 111.
AIRCON calculates air conditioning total
building cooling and heating loads, time of
maximum loading, and system air quantity
and temperature requirements. The program
uses data found In the "Cattier Load Estimating
Guide."
Fortran IV is used.
Deere and Co.
Zone Load Esti-
mation Program
(ZONEST)
Input follows the
"Carrier Load Estimat-
ing Guide." Addition-
ally it requires: number
of zones, temperatures
of hot and cold deck in
heating and cooling
seasons, system type
(dual duct, reheat, etc.)
Zone load, cfm, air change
summaries, dual duct system,
design and analysis, reheat
system design summary.
Operating;
B.Davis Deere and
Company
Moline, 111.
ZONEST is used to design or analyze new or
existing air conditioning systems. The program
computes the building zone heating and cooling
loads and determines the hour and month of
occurrence of peak loads in each zone. For
system analysis, the program compares actual
installed air volumes with design requirements.
The program calculates area and volume and
assigns supply air based upon a percentage of
sensible cooling load. It also computes air
quantity per square foot and the rate of air
change for each zone. Only sensible heat loads
are calculated.
Fortran IV is used.
(Continued)
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TABLE A-l. ENERGY MODELS - METHODOLOGY - INPUTS - OUTPUTS (Continued)
Model
(Code Name)
Input
Requirements
Model
Outputs
Date-Status
Developer
Descriptive Comments
Inatome Air
Conditioning
System Cooling
and Heating Load
Calculations
Program (A CLD2)
Occupant sensible and
latent heat losses,
ventilation code require-
ments, temperature
data, building charac-
teristics.
Room and zone heating/
cooling loads and peaks;
room and zone cfm's, air
changes, temperature infor-
mation, percent dehumidi-
fied air, smoke horsepower,
percent outside glass on air
conditioned air, net air
conditioned square feet.
Operating;
Inatome and
Associates, Inc.
The program finds the maximum heating and
cooling loads based on design criteria for each
room, zone, and building. From this it deter-
mines the required amount of air for each area
and reheat if necessary. The program is based
on methods outlined in the 1967 ASHRAE Hand-
book of Fundamentals. In addition, the wall
and roof gains in the program are based on the
sol-air temperature concept and equivalent
temperature differential equations. Program is
written in Fortran IV.
u>
i
National Bureau
of Standards Load
Determination
Program (NBSLD)
Building parameters
such as wall properties,
ceiling and floor prop-
erties, window area and
location, operating
schedules. Weather data
from U. S. Weather
Bureau tapes.
Hour-by-hour heating or
cooling loads and temper-
atures for each zone for the
entire year. Design day data
may be examined as an
option.
Written in 1972 is
continually revised
T. Kasada - NBS.
NBSLD calculates the hour-by-hour heating and/
or cooling load in buildings. The program
utilizes the thermal response factor technique
for calculating transient heat conduction through
walls and roofs. The program also includes a
routine which can calculate the "floating"
temperature of those rooms with little or no
air-conditioning and natural ventilation.
Fortran V is used.
(Continued)
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TABIE A-l. ENERGY MODELS - METHODOLOGY - INPUTS - OUTPUTS (Continued)
Model
(Code Name)
Input
Requirements
Model
Outputs
Date-Status
Developer
Descriptive Comments
Alternate Choice
Comparison for
Energy Systems
(AXCESS)
Weather data, base load
description, base load
profiles, design heating
and cooling load, space
type data, zone data,
HVAC system descrip-
tion, and output desired.
Energy consumption and
demand for each of up to 36
"meters" of the alternative
systems. Numerous optional
outputs.
Operating;
Seeyle, Stevenson
Value and Krecht
under contract to
the Edison Electric
Institute.
i
CO
O
AXCESS permits the simultaneous comparison of
up to six alternate methods for meeting the
energy requirements of a building. The program
may be used at various points in the design
process. If the structure is still in the conceptual
state, the program utilizes routines which approx-
imate the full input information which would
normally be available during the later stages of
design. The program calculates hourly zone
solar and transmission loads for the year (if not
input from another program). These bads are
utilized along with base energy loads to calcu-
late net zone space conditioning requirements.
Terminal system operation is simulated and
equipment energy consumption calculated in
one of three general subroutines.
Bridgers and
Paxton Energy
Analysis Program
Building block load
analysis using A PEC
HCC-HI program,
architectural descrip-
tion of building,
weather data, type of
system desired,
description of desired
system operation.
Daily summary of refriger-
ation and heating loads
along with boiler and chiller
input. On solar systems,
outside temperature,storage
tank temperature, solar
collector efficiencies! heat
collected by solar system
for each 3-hour period per
day, monthly and yearly
totals of heating and cooling
loads and corresponding
energy requirements.
Operating;
Dale R.Broughton
Bridgers and
Paxton Consulting
Engineers, Inc.
The program? calculates the yearly energy
consumption for heating and cooling buildings.
HVAC systems presently considered include
conventional dual duct system, conventional
single zone system, internal heat recovery heat
pump system, solar assisted heat pump system,
and solar heating and cooling system. Building
heating and cooling loads are determined using
3-hour weather data available from the U. S.
Department of Commerce National Climatic
Center. System simulation is performed, cal-
culating building refrigeration and heating loads.
For solar systems, a building heat balance is
performed. Performance of storage tank and
solar collector systems is simulated and its
overall effect on building heating and refrig-
erating load is determined for each 3-hour
period of the day.
Program written for IBM 1130 with 8K core.
(Continued)
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TABLE A-l. ENERGY MODELS - METHODOLOGY - INPUTS - OUTPUTS (Continued)
Model
(Code Name)
Input
Requirements
Model
Outputs
Date-Status
Developer
Descriptive Comments
Energy Conserva-
tion Utilizing
Better Engineering
(ECUBE)
i
CO
Maximum value and
hourly percentage pro-
files for internal heat
gain, electrical load
and process load trans-
mission and outside air
loads as a function of
ambient temperature.
Maximum solar load on
the building. Hourly
weather data. Heating
value of fuel. Part load
equipment performance
characteristics. Capital
cost differential for
alternative systems,
salvage values, mainte-
nance costs.
Monthly, annual and peak
energy requirements. Annual
fuel requirements for alter-
native systems. Cash flow and
discounted rate of return on
alternative investments.
Available in 1975
Continually updated
American Gas
Association
The ECUBE series of programs utilizes design
point calculations of peak thermal and elec-
trical loads to make hourly, monthly, and
annual estimates of the energy requirements
of a building. The energy consumption of
various types of systems which may be used to
meet these requirements are then calculated
and the program compares the total owning
and operating costs of the various systems being
considered. The program series consists of
three basic computer programs: (1) Energy
Requirements Program, (2) Equipment Selection
and Energy Consumption Program, and (3) Econ-
omic Comparison Program.
Honeywell Total
Building Simula-
tion (BULDSIM)
Building material
descriptions, building
descriptions, weather
data, mechanical
system, operating
model.
Load on interior and
exterior zones and fan
systems, energy require-
ments to maintain
operating conditions,
zone temperatures, dau y
totals, kw demand and
kwh profiles.
Written in January,
1974, Operating;
Dr.G.Shavit,
Honeywell, Inc.
The program incorporates the building envelope,
mechanical system, and the dynamics of the
control system to provide a "time" picture of
energy requirements and temperature distribution
in the building. The program takes into consid-
eration the dynamic characteristics of the
building material, heat storage, and time
constants of mechanical systems and controls.
The program provides a detailed output (every
minute), or integrated output for hourly, daily,
monthly, and annual summary of energy con-
sumption. Computer language used is
Fortran IV.
(Continued)
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TABLE A-l. ENERGY MODELS - METHODOIDGY - INPUTS - OUTPUTS (Continued)
Model
(Code Name)
Input
Requirements
Model
Outputs
Date-Status
Developer
Descriptive Comments
McDonnell
Douglas Auto-
mation Company's
Annual Consump-
tion of Energy
Program (MACE)
Weather specifications,
building and system
descriptions, months for
which calculations are
to be made, energy rate
structures, master time
schedules and appropriate
loads (such as occupants,
lights, appliances, etc.)
Hourly space and building
loads, electrical usage,-fuel
consumption, and cost of
carbon hourly bans and
monthly and yearly total
of each.
Operating;
McDonnell
Douglas Auto-
mation Company
MACE uses methods recommended by ASHRAE
wherever possible. The load calculation section
utilizes methods outlined in Proposed Procedures
for Determining Heating and Cooling Loads for
Energy Calculations. ASHRAE 1969. These
methods include the use of thermal response
factors for calculation of the transient heat
transfer through roofs and walls. The component
and system simulation section uses procedures
outlined in Proposed Procedures for Simulating
the Performance of Components and Systems for
i
to
CT>
ro
Energy Calculations. ASHRAE, 1969. The
economic section uses the local prevailing
utility rates, which are input into the program
by the user. The U.S. Weather Bureau is the
source of the following hourly weather variables:
dry and wet bulb temperature, wind velocity and
direction, cloud cover, cloud type, and baro-
metric pressure. MACE will accept sources of
weather data, once they have been prepared in
the proper format.
Meriwether
Energy Systems
Analysis Series
Engineering design data,
description of system
design and operation,
weather data, utility
rate structure,owning
and operating cost and
financial data.
Monthly and annual demand
and consumption of energy
for systems and equipment,
monthly and annual utility
costs, life cycle and cash
flow analysis.
Operating;
Ross F. Meriwether
and Associates,Inc.
San Antonio, Texas
The Energy Systems Analysis Series is a library
of computer programs which determine the
annual energy consumption of various types of
systems and equipment for a typical year of
operation, and determine the relationship
between these energy costs and other owning and
operating costs. The programs normally used in
conducting an energy analysis consist of the
Energy Requirements Estimate (ERE) which cal-
culates the hour-by-hour thermal and electrical
loads for a building, the Equipment Energy Con-
sumption (EEC) which simulates the operation of
the various pieces of equipment, and the Econo-
mic Comparison of Systems (ECS) which calcu-
lates the total owning and operating costs of each
system. A variety of auxiliary programs are
available to complement the basic analysis series.
(Continued)
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TAB1E A-l. ENERGY MODELS - METHODOlOGY - INPUTS - OUTPUTS (Continued)
Model
(Code Name)
Input
Requirements
Model
Outputs
Date-Status
Developer
Descriptive Comments
NASA's Energy
Cost Analysis
Program (NECAP)
Building parameters,
building coordinate
system, azimuth angle,
surface description and
tilt angle,floor, ceiling,
furnishing data, space
description, thermostat
schedules, type of energy
distribution system and
pertinent parameters,
cost information.
Response factors if requested,
summary of design day
weather, space and building
loads, surface shadow pic-
tures and shadow calcula-
tions, recommended space
heat extraction and addition
rates, variable temperature
loads if requested,zone air
flows, summary of loads not
met, equipment capacity
summary, monthly and
annual energy summary.
Operating;
Card, Inc.,under
contract to the
National Aero-
nautics and Space
Administration,
Langley Research
Center.
i
cc
CO
I
The NECAP program follows the procedures out-
lined in the ASHRAE booklet "Procedures for
Determining Heating and Cooling Loads for
Energy Calculation" to estimate the energy
requirements for buildings. The program is
actually a set of six individual computer pro-
grams including (1) a Response Factor program
(2) a Data Verification program (3) a Thermal
Loads Analysis program (4) a Variable Temper-
ature program (5) a System and Equipment
Simulation program and (6) an Owning and
Operating Cost program. Standard wall con-
struction and schedules can be used to simplify
program input. The program is an extension of
the Energy Utilization Program developed for
the U.S. Postal Service, but incorporates
extensive modification to improve its usability
including completely revised documentation.
Program for
Analysis of
Energy Utilization
in Postal
Facilities
Geometry of building and
its surroundings, thermal
and physical properties of
wall and roof construc-
tions, operating schedules,
weather data,four system
characteristics, chiller
operating characteristics,
and types of heating/
cooling combinations to
be examined.
Space sensible load, latent
load, return air lighting
load, lighting equipment and
power consumption are sum-
marized. Optional output
includes shadow patterns for
various building surfaces at
the hour designed.
General American
Research Division
of General Ameri-
can Transportation
Corporation.
The program (often known as The Post Office
Program) calculates the energy requirements for
heating and cooling of buildings via a two-step
calculation procedure. First, the hour-by-hour
heating and cooling load is calculated utilizing
the thermal response factor technique. The system
simulation portion then calculates the energy
required by the HVAC system to satisfy the imposed
thermal loads. An economic analysis program can
then be used to compare annual owning and
operating costs of various combinations of heating
and cooling plants. Fortran is used.
(Continued)
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TABLE A-l. ENERGY MODELS - METHODOLOGY - INPUTS - OUTPUTS (Concluded)
Model
(Code Name)
Input
Requirements
Model
Outputs
Date-Status
Developer
Descriptive Comments
CARD Program
forFacility/HVAC
Design and Energy
Analysis (SCOUT)
i
CO
Building construction
and orientation param-
eters, surface data,
optional shadow data,
space data, thermostat
schedules, space heat
data; optional average
specified air flows,types
of energy distribution
and conversion systems,
and pertinent cost infor-
mation.
Space and building peak loads
broken out into components;
optional surface and space
response factors, day weather
summary shadow pictures and
calculations; recommended
space air flows and heat
extraction and addition rates;
equipment capacity summary,
summary of space and systems
loads not met, monthly and
annual energy summary, space
temperature and pay back
period comparison of alter-
natives.
Available since
January, 1976;
CARD, Inc.
The SCOUT program follows procedures outlined
in the ASHRAE booklets "Procedures for Deter-
mining Heating and Cooling Loads for Energy Cal-
culations" and "Procedures for Simulating the
Performance of Components and Systems for
Energy Calculations" to estimate the energy
requirements for buildings. SCOUT is an. extension
of NASA's Energy/Cost Analysis Program (NECAP),
but incorporates complete data verification, full
set of self-instructional input forms, 13 distribution
system simulations, plus packaged systems and
heat recovery devices, and complete internal
restructuring resulting in reduced core requirements
and reduced running times.
Trane Air
Conditioning
Economics
(TRACE)
Building, system, and
equipment descriptions.
Economic factors.
Peak building loads, building
and equipment yearly and
monthly energy consumption.
Economic comparison of life
cycle cost for up to four
alternatives in one computer
run.
First available
in 1973, continu-
ally updated.
Applications Engi-
neering at the
Trane Company.
The program calculates peak and hourly zone loads
based on coincident hourly climatic data for temper-
ature, solar radiation, wind and humidity of typical
days in the year representing seasonal variations.
The average days are compiled based on the most
recent ten years of U.S. Weather Bureau data. The
design phase then receives input from the load
phase as well as system type information and zone
design information and calculates supply air
quantities and temperatures. The system simulation
phase utilizes hourly zone loads and calculates
return air quantities and temperatures and accounts
for system loads (such as reheat loads). The equip-
ment simulation phase takes the hourly output
from the system simulation phase and calculates
the annual energy consumption based on part load
performance data which is available on tape. The
economic phase then does an economic comparison
of the various design alternatives based on input
consisting of energy consumption data, utility
rate structures, and expected installation and
maintenance co*t>.
-------
A.2.2 Numerical Simulation of Infiltration and Indoor Air Movement
Infiltration Simulation
Although there are varying degrees of sophistication in the
methods by which total heating and cooling loads are computed by the
models listed in Table A-l, the portion of the total load resulting from
transfer of heat by air exchange between indoors and outdoors is usually
calculated by a method which simply assigns an air change rate for
computation based on building and occupancy type. The majority of the
energy consumption models utilize this simple procedure despite considerably
more complex modeling for other contributing loads. Three of the more
sophisticated models, NBSLD, NECAP and BEAM, utilize optional infiltration
or ventilation methods. In addition to the option of using the standard
air change approach, NECAP also provides the option of using the crack
length method. The NBSLD model provides for the option of using the
Achenbach-Coblentz infiltration correlation method. The BEAM program
provides the versatility of using any of the three methods; air change,
crack length, or Achenbach-Coblentz correlation; see equation (1) below.
The crack length method goes one step beyond a simple air change
approach and computes infiltration rates as a function of building opening
sizes and types, including windows, doors, and vents. The accuracy of this
method is dependent upon precise description of the building openings.
The Achenbach-Coblentz method utilizes a wind speed and
temperature correlation for estimating infiltration rates. The correlation
is of the form
I = A + BV + c|AT| (1)
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where:
I = Infiltration rate in air changes per unit time
V = Wind speed
T = Temperature difference between the interior of
the building and the outside
and A, B, and C are constants characteristic of the building being
analyzed. Under zero wind and temperature difference conditions the
Achenbach-Coblentz correlation reduces to the constant A. This represents
a constant infiltration term due to opening and closing of doors and
windows, the operation of various fans, and possibly other unidentified
infiltration mechanisms.
The infiltration due to wind is governed by the constant B
in the correlation. The coefficient represents the results of an air
flow balance of individual flow paths across windows, doors, and walls.
In the absence of wind, fan operation, door opening and closing,
and combustion air requirements, there remains another driving force for
inducing infiltration. Temperature differences between the interior
and exterior of a residence produce different air density gradients
with altitude. The phenomenon is known as the chimney or stack effect.
In the winter, for example, the stack effect produces a higher pressure
outside than inside at the lower levels of a residence. The reverse is
true for the upper levels. In most cases, a neutral zone exists somewhere
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between the upper and lower levels, where the net pressure difference is
zero. The net result for the winter is that the outside air flows in
through the crackage in the lower section of the house and the warm inside
air escapes through the upper section openings. Reverse flow conditions
occur during the summer. The Achenbach-Coblentz correlation takes this
into account through the CJATj term.
Indoor Air Movement Simulation
None of the infiltration calculation routines, as used within
available energy conservation models, are capable of accurately describing
infiltration and ventilation flows within the building itself. These
routines are chiefly concerned with the heating and cooling loads due
to the flow of outside air into the buildings. There are, however,
ventilation models which are basically air movement simulation models,
concerned with accurate description of air flow patterns within structures.
Three such programs, the Residential Infiltration Program (RIP), the
National Research Council of Canada program (NRC), and the Air Movement
Simulation Program of NBS, are described below:
I. The RIP infiltration program evaluates individual contri-
butors to the overall infiltration rate within residential buildings.
The computer program performs a flow balance on a given residence.'. The
residence is specified in terms of window, window frame, door, and wall
characteristics., In addition to the component type, size, and number
specification, the program can be supplied with steady state positive or
negative exhaust rates. This aspect permits the simulation of exhaust
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fans, furnace operation, and positive pressurization which may be used
for the purpose of eliminating infiltration. The external environment
is specified in terms of wind speed and direction.
The program uses the wind speed to compute the stagnation
pressure and then applies a cosine distribution of pressure, on the
basis of the relative angle between the wind direction and the plane of the
wall, to compute the pressure on the outside surface of each wall. These
pressures, in conjunction with a flow equation, are used to solve for the
unknown internal pressure using iteration methods. Once the inside pres-
sure is determined, the program evaluates the flow rates across each
component as well as the overall infiltration rate.
II. The primary objective in development of the NRC computer
program was to study the smoke movements in the buildings in the case of
fire. This program has been utilized to develop correlations between
infiltration rate through buildings as a function of ambient tempera-
ture, wind velocity, and wind direction. The mathematical model
of this program is represented by a set of compartments stacked one
on top of another and by a set of shafts that pass through all the
compartments. Leakage openings are present in each outside wall of each
compartment and in all the floors and shaft walls so that air can pass
from every compartment to adjacent compartments and to each of the
vertical shafts. Each compartment may represent one story of the building,
or may represent a number of stories in order to save computation costs.
Each shaft may have two vents to the outside. Vent openings are designated
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"top" and "bottom," but they may be located at any level. The effects
of the air handling systems are accounted for by specifying the net
quantity of air supplied to each vertical shaft and to each compartment.
Stack effect (see discussion under Infiltration Simulation above) is
calculated for any given outdoor temperature.
The flow equation used 1s
F = EA UP)X (2)
where
F = flow rate through a leakage opening (cfm)
EA = flow coefficient (cfm/in2)
AP = pressure differential (in*)
x = flow exponent (0.5 f x < 1.0).
In order to account for the effects of wind, the pressures due
to wind on each face of the building at each level must be determined. The
developers of the NRC program recommended that this be done by specifying
a matrix of wind pressure coefficients which relate the wind pressures at
each level to the ambient wind velocity pressure, based on the wind speed
at a height of 30 ft as measured by a meteorological station. A more
realistic vertical profile of wind speed and directions, introducing a
vertical wind speed gradient and turning, could be introduced into the
matrix if desired and if data are available. These wind pressure coef-
ficients account for wind velocity profile, ground effect, and shading
effect by other buildings. Coefficients could be obtained from wind
* Inch of water 4°C equivalent to 5.216/ft2, which is the pressure of one-inch head of water.
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tunnel tests on a model of the building. Wind pressure coefficients
for each level and for 16 directions must be specified with the other
data.
The following assumptions made by NRC constrain the model:
Frictional resistance of vertical shafts is
neglected
Net air supplied by the air handling systems is
assumed to be constant and independent of building
pressures
The building has an open floor plan with no
provision for separate rooms or vestibules
Pressures, flows and leakage openings are assumed
to occur at mid-height of each level
t Temperature inside compartments and shafts is
assumed to be 75°F.
The flow balance equations for each compartment and each
shaft are:
for the 1th compartment,
JJ
Fo(i,k)+ Fb(i) - Fa(i) - £., Fs(1,j) + Fac(1) = °
and for the jth shaft, (3)
NN
£, Fs(1,j) + Fbv(j) + Ftv(j) + Fsh(j) = °
where
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k) ^rom outslc'e through side (k) to compartment (1)
^°" ^rom con)Partnient below to compartment (i)
flow from comPartment (1) to compartment above
j) = ^w ^rom comPartment (i) to shaft (j)
net "f1°w °f alr supplied to compartment (i) by air
handling system
^bv(j) = ^ow 1n*° sna^t (J) through bottom vent
Ftv(j) = f^ow ^nto sna^t ^J) through top vent
F _u/j\ = net flow of outside air supplied into shaft (j) by
snu' air handling system
NN = number of compartments
JJ = number of shafts.
Combination of mass balance Equations (3) and (4) with flow Equation (2)
results in a set of simultaneous non-linear equations. The outside
pressures and the pressure differences due to column weight may be cal-
culated from the input data.
These simultaneous non-linear equations are solved by a method
of successive linear approximations. The non-linear function described
by Equation (2) is shown in Figure A-l. In the region near point (APt,Ft)
this function may be approximated by a straight line which is tangent to
the curve at this point. The equation of this linear function is
F = K1 AP - AP1 (4)
where
K1 = K x APtx-1
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and
Each leakage flow in Equations (3) and (4) may be expressed by this type
of linear approximation. The resulting set of NN + JJ linear equations
for the pressures can then be solved by standard methods.
F A
F ~~ K (AP)X
APi
APt
AP
Figure A-l. Linear approximation of flow equation.
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The iteration method is as follows: an initial linear approx-
imation is made for each flow and the resulting equations are solved for
space and shaft pressures. The flows corresponding to these pressures are
then calculated, and the flow through each element is compared with the
flow used for linearization of that element. If the difference is greater
than the convergence criterion (a criterion supplied by a variable "error"
in a special subroutine which for this work has the value of 0.1 cfm)
that element is re-linearized about the most recently determined flow and
the linear simultaneous equations are solved again. This procedure is
repeated until the flow through every element satisfies the convergence
criterion.
III. NBS Air Movement Simulation Program
This modeling program was developed by Integrated Systems,
Inc., for the National Bureau of Standards for the purpose of studying smoke
patterns within buildings. The program, which simulates vertical and
horizontal air flow patterns inside a building, is the most comprehensive
air movement simulation model presently available. It is described in
considerable detail in the following pages because its description will
provide the interested reader with an opportunity to understand basic
principles alluded to in briefer descriptions of other models in this
chapter. A careful review of this model will also demonstrate the
difficulty of reducing the complex behavior of indoor air movement to
manageable parameters for modeling.
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The primary design goals of this NBS program are to achieve a
realistic representation of building spaces and HVAC (heating, ventilation
and air conditioning) systems, and to achieve realistic flow relationships
in the simulations. The design of that part of the computer program which
simulates air movement is based upon an already existing preliminary
design. The new elements in the NBS program are principally the detailed
logic necessary for handling large quantities of data and the numerical
analysis necessary to achieve solutions.
The major problem with earlier air movement simulation models
had been the lack of realistic modeling ability for the spatial con-
figurations of buildings and of the components and configurations of
HVAC systems. The design utilized in the NBS program has the following
descriptive capability:
1. Up to 100 floors of a building
2. A single corridor on each floor
3. Up to 10 compartments on each floor, which can be
related to zones, suites, or specific spaces
4. Up to 25 HVAC systems, each composed of:
a. An air handling unit (AHU) (blower/fan)
which delivers air to the supply duct network
b. A supply duct network
c. A return air duct network or plenum
d. An outside air supply shaft or duct to the
AHU inlet
e. A return air coupling to the AHU inlet to supply *
recycled air
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f. A means to provide any mixture of outside air
(OA) or return air (RA), from 100-percent OA to
100-percent RA, to the AHU
g. A ventilation shaft or duct to exhaust return air
not recycled
h. An exhaust fan for the ventilation shafts.
5. Up to 20 different fans/blowers for use anywhere in the
building/HVAC system
6. Up to 90 shafts or ducts made up of any combinations of
the following, except as indicated:
a. Elevator shafts to a maximum of 16
b. Stairwells
c. Air supply ducts/shafts
d. Ventilation ducts/shafts
e. Cable/pipe/duct shafts
f. Window HVAC unit pipe shafts.
7. Up to 70 sets of non-fan/blower coupling parameters
8. Up to 10 external wind functions which are linearly
variable as a function of height
9. Up to 20 single temperature values for spatial temperature
specification and 20 temperature-height functions for
shaft/duct temperature specification.
Other features of a building which can be described in the program include:
1. Inlet fans/blowers to pressurize shafts, such as stairwells
2. HVAC air supply to stairwells
3. External leakage to:
a. Corridors
b. Compartments
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c. Stairwells, to a maximum of 20
d. HVAC window unit shafts
4. Ventilation fans from corridors and compartments
to ventilation shafts and directly to the outside
5. Outlet fans from the various forms of shafts.
Although all characteristics of all building HVAC systems cannot be
specifically represented by the capability of the computer program
developed, the functional representation of almost all characteristics
can be modeled by appropriate use of the available characteristics.
In the development of the NBS program it was initially planned
that the basic numerical solution of the program would be obtained by
the use of linear simultaneous equations and a linearizing technique for
non-linear equations. There are 1,265 possible non-linear equations in
the program. This large number of equations, together with the variability
and number of allowable boundary conditions, and the variability of the
forms which arbitrary equilibrium equations may take, combine to create
a very difficult problem for such an approach. To obtain solutions, it
would be necessary to develop a computer subroutine to generate the elements
of the coefficient matrix. It would also be necessary to develop a
subroutine operating on the generated, square matrix to reduce it to some
form that can be easily treated within a computer memory, such as a band
or triangular matrix. Past experience in developing such computer programs
for highly variable systems, which had regular and symmetric matrix properties
(as compared to the skewed matrices which would characterize the NBS program)
and regular and well-behaved boundary condition definitions, indicated that
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such an undertaking was not feasible within the time and resources
available. Consequently, this approach was abandoned and another
sought.
The method subsequently chosen for the solution of the NBS
Air Movement Simulation Program was the use of nested, iterative solutions.
The method is straightforward, allowing relatively easy handling of the
data. The nested, iteration approach is usually more costly in computer
time required than is the matrix approach, but this would not be the case
with the angular skew inherent in the NBS program.
Two other factors weighed heavily 1n favor of the nested iterative
approach. One factor was the certainty of fitting the computer program into
normal and readily available computer memory partitions, whereas a great
deal of doubt existed with the linear system approach. At the least,
special treatment of the memory space or the data (e.g., temporary storage
on auxiliary memory devices) would have been required. The second factor
was that the use of matrix Inversion techniques frequently leads to no
useable results emanating from the computer output when highly skewed
angular systems are encountered. In the case of the nested iterative
approach, useable data can be obtained even though exact solutions (i.e.,
satisfaction of the convergence criteria) are not achieved.
The fundamental basis of the NBS computer program simulation
of the steady-state air movement in a bullding/HVAC system is the mass
flow rate equilibrium equation; I.e., for a given building space or
HVAC component, denoted by the index, j,
Flj + F2j + + Fij + + Fnj = °'
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where F^ . 1s the mass flow rate of air between the i and j building
spaces and HVAC components.
This equation is solved for each corridor and compartment on
each floor, for each shaft, for each supply duct network, for each
return air duct network, and for each AHU. The system of equations that
must be solved in each case is completely dependent upon the building HVAC
system modeled by a user from these available components and the imposed
conditions provided.
The mass flow rates between any two building HVAC components
are based upon the type of passage between any two components, i.e.,
large, moderate, or very small (crack). In the case of a large opening,
such as an open doorway, a vent or register, etc., the mass flow rate
1s determined from Bernoulli's steady-state equation, with some head
loss, i.e.,
F = kA ./ZgW (6)
where
p
A is the effective opening area (ft )
k is the flow coefficient, ranging between 0.6
and 1.0
P is the density of air of the inlet side (lb/ft3)
and
is the pressure difference between the two
components or across the opening (Ib/ft2).
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For moderate openings, such as under a door, around an elevator
door, etc., the same form of Equations (5) and (6) is used as for the
large openings. However, a contraction coefficient (due to contraction
of flow) and an approach factor have been combined into a single
coefficient, k, which is a function of geometry and Reynolds number. In
this case, the coefficient k ranges between 0.2 and 0.3.
For very small openings or cracks, such as are found around
windows, it was assumed that the mass flow rate could be expressed as
F = C A?" (7)
where
n is the flow exponent, between 0.5 and 1.0
and
C is the flow equation.
It was also assumed that the flow through such passages would obey
Darcy's law (7). Hence,
n = 1
For simplicity, the above three forms of expressing mass flow
rate for different openings were reduced to a general form, sometimes
referred to as the orifice equation, i.e.,
F = k Px u1"2* APX (8)
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where
Is determined as a function of the type o.f
opening, the effective area, and the appropriate
flow coefficient for the above types of openings
is 0.5 for the large and moderate openings and 1
for the very small or crack-type opening
and
p and AP, as defined above, and p are the viscosity of
air on the inlet side of the opening.
The program was designed to allow a user to specify k and x
or the effective area A and the type of opening. If the latter option
is utilized, the flow coefficients are determined as follows:
1. For a large opening
k = 0.8
»
2. For a moderate opening
k = 0.25
3. For a very small opening or a crack
k = 0.1
External wind leakage can be a significant factor in the
effectiveness of an HVAC system and, under certain conditions, can defeat
the use of an HVAC system in controlling pressures within a building.
Consequently, significant capability is provided to define varying
external conditions operating on the external walls of the simulated
building. As indicated, 10 external wind states were included in the
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design of the computer program. Each of these states was then defined
as wind speed, normal to the wall, varying with height, and at a given
temperature. Temperature was held constant for each wind state, i.e.,
V=f(hi) (9)
where
f(h^, T) is a tabular function
and
h1 is the height at the ith point.
Excluding an exhaust fan or intake blower interfacing directly
with the outside air, all of the air flow in or out of the simulated
building is determined as a function of the pressure difference.
Consequently, the pressure due to the wind at any given floor level
and on any given external wall must be determined. The dynamic pressure
due to the wind is defined as
d
where
P., - V2 P V2 (10)
2
is the dynamic wind pressure (Ib/ft )
is the density of the outside air at the given
height and temperature (Ib/ft3)
and
is the wind speed at the given height on the
given external wall (fps).
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Critical to a realistic simulation is the representation of
the behavior of air within an open shaft, such as a stairwell, elevator
shaft, or plumbing chase. Two basic situations are usually encountered
with such shafts: (1) a non-pressurized shaft which is coupled for air
movement purposes by leak passages, and (2) a pressurized shaft with
specific and designed flow openings as well as leakage openings.
The basic approach to the solution of the equilibrium condition
within a shaft was based upon an automated selection of the most significant
flow point to control the solution at the convergence pressure. Continuity
was maintained by calculating the pressures at all other floor levels as
a function of height, positive or negative, from the reference, or
convergence, pressure.
In general, the upward or downward recursion relationship
utilized was expressed as
(PI + Pi+l)
Pi - Pi+1 - (h1+l - h^ - 2 - (11)
where
th
P. is the pressure of the .mid-height of 1
floor level
P,+1 is the pressure of the mid-height of the i+l
floor level
hi is the mid-height of the ith floor level
hi+1 is the mid-height of the i+lth floor level
P. is the density of the mid-height of the ith
floor level
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and
P,., Is the density of the mid-height of the i+lth
11 floor level.
Since density is a function of pressure and temperature and
these two variables can vary with height, it 1s necessary to solve the
above expression for pressure, both for the upward and downward cases,
by substitution of the density relation into the equation.
The continuity condition and the equilibrium condition are
solved simultaneously to determine the pressures within an unpressurlzed
shaft.
In the second case, i.e., where an inlet blower existed and
a pressurized condition existed, another relationship was introduced to
include the effects of the blower or fan pressurizatlon. The duct
equation is introduced to provide a means of determining the vertical
pressure distribution within a pressurized shaft, i.e.,
AD 0.0533 T F^ | Ah
TO ~
10 I 5/2
0.7854 PIO
where
APTn is the pressure loss between the fan inlet to
the shaft and the major outlet (PSF)
T is the average temperature between the shaft's
inlet and outlet (°R)
Ah is the distance between the shaft's Inlet and
outlet (ft). (In the case of a stairwell, a
spiral ing factor is included.)
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A is the average cross-sectional area of the
shaft between the inlet and the outlet (ft2)
"p is the average pressure in the shaft between
1U the inlet and the outlet (PSF)
and
Fn is the mass flow rate at the shaft outlet
u (Ib/min).
The duct loss equation is solved as an implicit function iteratively,
where
F0 *(P0. Pext) (13)
P10 = *(P0. Pr) (14)
and
PO is the pressure at the outlet
ls ^e pressure on the external side of the
outlet
Pj is the pressure in the shaft at the inlet.
The loss is assumed to occur between the inlet point and
the outlet point, where either one could be above or below the other.
The loss distance is assumed to be the distance between these two
locations, except in the case of a stairwell. In the case of a stairwell,
a lengthened channel is assumed, due to the spiraling nature of a
stairwell, and the vertical distance between the defined inlet and
outlet was multipled by a lengthening factor.
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The loss in pressure was Included in the continuity condition.
A linear relationship 1s used between the inlet and the outlet to provide
the vertical distribution of the pressure loss. If a shaft extends
beyond an Inlet or outlet away from the other, a stagnant condition 1s
assumed, with pressure equal to the Inlet or outlet, respectively.
Initially, an attempt was made to represent a fan or blower as
a function of typical fan or blower characteristics and the air state
at either the Inlet or the outlet. However, the conditions were of a
variable nature and could not be satisfied with the expressions attempted.
As a result, two methods of specifying a fan or blower, both of a simple
form, are utilized.
The first method allows a user to specify a blower rotational
speed (RPM), horsepower, and an outlet area. From tabular data representing
a family of fans/blowers, throughput Is determined, I.e., static discharge
pressure and volume flow rate at standard conditions.
The second method allows a user to specify the static discharge
pressure and the volume flow rate under standard conditions.
In either case, the volume flow rate is converted to mass flow
rate; I.e.,
FB = QBPS (15)
where
rB
is the mass flow rate output of the blower/fan
(Ib/m1n)
Qn 1s the specified volume flow rate output of the
B blower/fan (SCFM)
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and
pc is the density of air under standard conditions
S (Ib/ft3).
The mass flow rate from a specified blower enters the equi-
librium equations coupled at the blower/fan, except in the case of an
outlet or inlet fan or blower, as effectively a boundary condition;
i.e., the mass flow rate for that component is fixed and not allowed
to vary as a function of the iterative processes.
The given static discharge pressure is of particular Importance
in the case of pressurized shafts and enters the solution via the duct
loss equation in the continuity relationship. In other cases, where
the flow only enters the equilibrium condition, the given static
pressure is not directly used.
In order to provide as realistic a simulation as possible,
particularly with regard to simulating pressure differences, air density
was not assumed as constant. Air density is calculated at each point
in the programmed process where it was required, as a function of the
temperature and pressure of the building space or HVAC component Involved
in the calculation; i.e., at a constant height,
_ 0.0187618P
p- T
where
P is the pressure
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and
T is the temperature (°R).
Since the air within an open shaft is treated as a continuous
medium, i.e., the pressures were determined as a function of the control-
ling flow, e.g., an inlet blower, and as a function of height, the density
becomes appropriately variable as a function of height.
The determination of the viscosity of air 1s purely a
function of temperature. A linear segmented curve fit was made over the
range of anticipated temperatures. The representation utilized is as
follows:
M - a + bT (17)
where
a = 3.4 x 10"7
b = 0.006 x 10'7
for
0 < T < 125
and
a = 3.5 x 10"7
b = 0.0052 x 10~7
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for
125 < T < 250
y is 1n Ib sec/ft2
and
T 1s 1n °F
The NBS air movement model, and the earlier discussed RIP
and NRC models as well as the energy numerical models, which were
described 1n Table A-l, have major thrusts which are not directly related
to Indoor air quality determination. They have, however, been described
here because the concepts developed and used in these models are relevant to
the investigation of numerical analysis for Indoor-outdoor air pollution
models, particularly in that they provide methods for calculating infil-
tration, exfiltration and ventilation rates which are parameters of
great Importance 1n the Indoor-outdoor pollution models. In addition,
the energy models provide fundamental elements for future efforts to
study the optimization of desirable energy consumption measurements and
low Indoor air pollution levels.
A.2.3 Indoor-Outdoor Air Pollution Models
The subject of relating the outdoor ambient and indoor air
pollution levels is relatively recent and research emphasis has been
placed on field measurements of air pollution rather than upon the
development of numerical models to describe indoor-outdoor air pollution
relations. It 1s not, therefore, surprising that the number of existing
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models 1s small. Five models relating indoor and outdoor air pollution
levels were identified in the research literature. These are reviewed
in following pages. A number of them were developed for purposes other
than describing Indoor-outdoor air pollution relations in buildings;
some of the early work was done in connection with chemical warfare
problems. Where necessary, the relevance of these models to the
indoor-outdoor air pollution problem in buildings will be stated.
The Effective Residence Time Model
The effective residence time model establishes a functional
relationship among the three fundamental parameters of ventilation rate,
residence time, and concentration. It has some severely constraining
assumptions which limit its application to reality, but it is a useful
step toward understanding indoor pollutant dispersion. The theory
developed has been formulated independently, and utilized in various
projects by Milly [426], Constance [138], Drivas et al. [171], and others.
The model 1s based upon an equation relating the volume of an
enclosed space, air flow between outdoors and indoors, and pollutant
concentrations:
-Vdc = cvdt (18)
In this equation V indicates the volume of an enclosure in m^,
o
v is the rate of entry or egress of air into the enclosure in m /hour,
and c is the initial concentration of a pollutant inside the enclosure
1n mg/m. A ventilation rate, appearing in subsequent equations, is
defined as a = v/V air changes per hour. A constraining assumption of
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the model 1s that the generation of the pollutant ceases at the instant
of measuring Its concentration, an assumption which presents difficulty
in using this model to simulate realistic behavior of some pollutants in
residential environments but which was appropriate for many of the military
uses for which the model was first developed. It 1s appropriate for
considerations of pollution dispersion from aerosol sprays or from other
short-peak pollutant generators. The model assumes that in time dt the
pollutant concentration decreases by dc which corresponds to a total
decrease of Vdc mg. The volume of clean air entering the enclosure
through the various "breathing" outlets of the structure during this time
is Vdt, which is also the volume of contaminated air that leaves the
building (the assumption has been made that ambient air entering the
structure after the moment of measuring the initial concentration 1s
pollutant-free). The contaminated air that leaves the enclosure contains
cvdt mg of the pollutant. The flow is defined, as stated before, by
-Vdc = cvdt (18)
Integrating between the appropriate limits
CQ
where c and c^ refer to an initial and final concentration at time t = 0
and
t = tf = t-final, respectively; it is
In f- - - at
o
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and
c = c0e-at (20)
Equation (20) provides the time history of the concentration
of a pollutant given the value of the ventilation rate a. It is seen that
the effective residence time, equal to the time for one air change, is
the inverse of the ventilation rate, a, (t = I/a = V/v). Details on how
to experimentally measure the ventilation rate of a structure will be
given in a subsequent section of this chapter. This approach is similar
to the theory developed by Constance [138] who used the mixing factor
K. His equation, corresponding to Equation (20) in this text, is
(21)
where values of K vary from 1/3 to 1/10
The major assumptions in this approach, and some of the dif-
ficulties to be expected in using the model, may be summarized as follows
t Implicit in this theory is that the ventilation rate
estimated is an overall rate; it includes infiltration,
cleanup, circulation and re-entry of the air.
It is assumed that the source of the pollutant intro-
duces a certain concentration of the pollutant and stops
operating (as in the instantaneous explosion of a gas
munitions shell, the operation of a controlled aerosol
spray, the passage of a transient puff of pollutant,
or the turning on and off of a combustion source). The
initial pollutant concentration is generated in one of
two ways: (a) an inside source operates for a short
time and then it stops, or (b) an ambient pollutant
concentration appears as a cloud just outside the
-3Q1-
-------
enclosure. A corollary of this is that the pollutant
concentration Inside the enclosure 1s assumed to disperse
under the influence of infiltration of pollutant-free
ambient air.
The ventilation rate "a" is representative of the
meteorological conditions prevailing during the intro-
duction and monitoring of the tracer; at least three
different sets of meteorological parameters should be
investigated because the ventilation rate varies with
respect to the wind, the temperature and the pressure
gradients indoors and outdoors.
These assumptions and difficulties notwithstanding, the effective
residency time approach is a powerful tool in modeling indoor pollution
concentrations because it is compact, simple, and can be applied to many
situations to meet or approximate the assumptions made. The next model
to be described under the generic term of 'dosage1 models is more detailed;
it considers sources inside and outside the enclosed space and it provides
for the existence of indoor pollution sinks.
The Dosage Model
The dosage modeling approach outlined in this section was proposed
by Calder [103] in studying air penetration of buildings. This approach
has been implemented in modeling penetration of dense vegetation by
Milly and Thayer [428]. The framework of relating indoor air pollution
levels to outdoor air pollution levels can be modeled in terms of dif-
ferential equations. The component-approach followed in the dosage model
differentiates it from the residence time model outlined earlier; the
dosage model does not require all the assumptions made before but it is
subject to its own constraints. It is more detailed, requires field data
obtainable only over extended periods of indoor and outdoor monitoring,
and requires extensive computer usage for its implementation.
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The dosage model takes Into account the several processes that
cause different amounts of airborne contaminants (gaseous or participate)
to occur Inside a building: (1) air taken Into the building through
windows and doorways, ventilation systems and cracks or leaks throughout
the structure; (2) removal arid decay processes Including filtering and
absorption by entry channels, oxidation, settling, absorption and
adsorption by walls and furnishings, Interior circulation filtering, etc.;
(3) Interior generation from sources such as fireplaces, stoves, smoking,
cleaning and others; and (4) air exhaust through chimneys, windows, doors,
vents or other exits. A small differential change in the amount of
interior contaminant results 1n the following mass balance equation
modeled 1n terms of the above processes:
dQ (1 - k) rx dt -
-------
If the above expression is divided by V, the interior volume,
recalling that
(23)
the result obtained is
dXi = (1 - k) £ xQdt - (y + <) Xldt + $ dt (24)
p 1
Substituting R = L= ventilation rate (hr )/ the equation becomes
d = [(1 - k) RX(j - (R + <) Xi + ^] dt (25)
To use these equations prior knowledge is needed of the values
of signature parameters such as the ventilation rate, filtering
characteristics, decay rate, and pollutant concentrations indoors
and outdoors. The approach is oriented towards a particular structure; the
results refer to the Investigated structure, to its type of a ventilating
system, to the climatology or meteorology and to other specific conditions.
The filtering constant k is a function "of particulate size for aerosols
and of the concentration for gaseous pollutants; it also depends on the
condition and maintenance of the filter systems. The removal or decomposition
rate (K) depends on the type of pollutant being considered as well as
particulate size and the nature of the indoor environment. Studies of these
parameters have been undertaken in the past and there is some information
available for certain types of structures; details are presented later in
this chapter.
-394-
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Returning to the mathematical formulation of the dosage model,
if Equation (25) is Integrated with respect to time over a monitoring
period t (the parameters remaining constant over a short sampling period
tg). Equation (25) becomes
S - (1 - k) R / S x0dt - (R + k) f S x,* + ^ (26)
00 0
The time Integrated concentration observed over sampling time
is defined as a dosage
Drt = I x dt = ambient outside dosage
° J o
o
*
. = I x-
= ambient inside dosage
Under the sampling assumption the dosage is defined as the product of the
pollutant concentration and the time period of sampling for both the
inside and outside environments. Now Equation (25) becomes
Xi(ts) - Xl(t-0) = (1 - k) RDQ - (R + K) D1 + li (27)
Equation (27) provides the relative pollutant concentration
change over a certain time period as a function of the outdoor and
indoor dosage, and the generation and decay rates of indoor pollution
sources and sinks over the same time interval.
-395-
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The concept of dosage, widely used 1n studies of chemical
warfare by Milly and Thayer [430] and others, is of fundamental
importance in designing monitoring strategies and in defining different
building parameters. Several hypotheses may be examined relative to
the Equation (27) in order to determine sampling procedures. For
instance, it may be difficult or impossible to measure instantaneous
inside concentrations of some pollutants, e.g., particulates. If
sampling is done over a sufficiently long time period, the difference
in initial and final concentrations may be assumed to be unimportant
relative to other terms in the equation. If the generation of the
pollutant from inside sources is also negligible the model reduces
to the following form
(1 - k) R _ (28)
D0
where
B = penetration ratio between accumulated inside and
outside dosages.
If the penetration ratio is found to be near unity for a particular
pollutant the effect of intake screening (k) and decay and removal (<)
are negligible for that pollutant. Careful measurements of the inside
and outside concentration histories of such pollutants can be used to
establish the building ventilation rate. For instance, if the generation
of pollutant from inside sources is negligible and < = k = o, then
-396-
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R = MV " nu' (29)
This equation gives the average ventilation rate over the sampling
time period t .
The impact of a controlled airborne material, such as an inter-
nally released inert gas, for determining ventilation rate can also be
seen in the above equations. In this case the outside concentrations
can be considered negligible and the pollutant intake can be ignored.
Since the gas is inert, it may be assumed that < = 0. Thus, the only
measurements required to determine the ventilation rate are the internal
concentrations. The equation is
R .
. *1(0) - Mt.) (30)
D1
Equation (30) provides an easy way of determining the overall
building ventilation rate by introducing in the structure known concen-
trations of an inert gas, such as SFg.
The power of the dosage model lies in its realistic approach
to sampling because it does not necessitate instantaneous concentration
readings which are indeed difficult for certain pollutants. It should
be noted that the stated assumptions for various strategies can be
achieved by imposing them, e.g., ceasing the generation of the indoor
pollutant, q = 0, closing the various breathing vents, k = 0, or
introducing an inert agent, < = 0, and by sampling for long periods
-397-
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so that the difference between the initial and final concentrations
may be assumed unimportant relatively to the other terms.
The "Well-Mixed" Tank Theory
A comprehensive theoretical study of the behavior of odorous
vapors in the chambers was developed by Amos Turk [634]. Although this
work specifically refers to odorous vapors the analytical principles involved
are general and can be applied to all air pollutants. Turk's work has
been utilized 1n subsequent studies relating indoor-outdoor pollution
levels. His theoretical development 1s known as the "well-mixed tank"
theory.
The theory 1s applicable to the general case of a chamber
which contains an odorous vapor. The following processes are considered:
A constant additional amount of vapor is generated,
or injected into, the chamber per unit time
The chamber air is being replaced by air
from outdoors by ventilation or infiltration
Sinks (vapor reducing devices) treat the
chamber air.
A basic premise of the theory 1s that instantaneous and complete
mixing of outdoor air takes place within the chamber. This is obviously
not a wholly realistic model of what occurs, but provides an adequate
representation of reality for the purpose of this model, which is to
estimate a single average concentration value for odors (or other pollutants)
Inside air enclosed space. The premise is, in fact, common to all existing
*
indoor-outdoor pollution models, in that they do not predict nor use data
describing indoor pollution concentration gradients.
-398-
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The notation which Turk used in his studies is as follows:
V = volume of chamber
t = time
C = concentration of vapor in chamber at any time
CQ = initial concentration in chamber
C^ = concentrations of vapor in chamber at equilibrium
C.j = concentration of vapor in ventilation or infiltration
C = concentration of vapor delivered by the air treatment
device
E = efficiency of vapor reduction by the air treatment device
Qj = volume rate of ventilation or infiltration
Qr = volume rate of air delivery by the air treatment device
G = quantity rate of generation of vapor within (or injected
into) chamber
N = number of air changes
m = mixing factor
X » quantity of vapor in chamber.
At any given moment
C = X/V or X = VC (31)
The vapor quantity X changes with time, dt, in the following fashion
dX = VdC (32)
This change is caused by three factors:
-399-
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1. Generation = Gdt
2. Infiltration or ventilation: - (C-Cj) Qj dt
3. Vapor reducing device: - (C-C ) Q dt.
It is E = (C-Cj/C which leads to the device
' effect: - CEQj. dt
The total change dX follows the sum of the three factors
dX = VdC = Gdt - (C-Cj) Q1 dt - CEQf dt (33)
and
-VdC
LC
= dt (34)
Integrating Equation (34) between CQ and C we obtain
V , . .
1n (Q,+EQr) - (C^^1
or in a more practical form
/C.Q.+G
C = CQ exp [- (Q1+EQf) t/V] + (
(1 - exp [- (Q1+EQr) t/V]} (36)
The case of equilibrium 1s denoted by t -*«>, hence any e term goes to
zero and Equation (36) becomes
(37)
-400-
-------
In his theoretical study Turk analyzed nine special cases:
Case 1: Ventilation air 1s pure (C^ = 0), and
C - CQ exp [- (Qj+EQ,,) t/V] + (Q g£Q } {1 - exp [- (Q^EQr) t/V]} (38)
Case 2: No Internal sources or Injected vapor concentrations (G 0), and
C-Q,
C = CQ exp [- (Qj+EQ,.) t/V] + (Q ^ } (1 - exp [- (Q^EQr) t/V]} (40)
and
Case 3: The vapor reducing device Is 100% efficient (E = 1 and C,. = 0),
and " r
C = CQ exp [- (Q^Q^ t/V] + -- {1 ' exp [- (Q+Q) t/V]> (42)
and
Case 4: The chamber 1s originally pure (CQ = 0), and
- exp [- (QEt t/V]} (44)
-401-
-------
and
C = J L. = the general equilibrium equation (37)
08 ^ ^
Case 5: The chamber (room) 1s tight (Q^ - 0), and
C = CQ exp (- EQr t/V) + E§~ [1 - exp (- EQp t/V)] (45)
Case 6: Combinations of Cases 1 and 2 (C^ = G = 0), and
C = CQ exp [- (Q1+EQr) t/V] (46)
and
CM = 0 (47)
Case 7: Combinations of Cases 1 and 3 (C1 = 0, E = 1, C = 0), and
C - CQ exp [- (Qj+tg t/V] + (Q^Q j (1 - exp [- (Q1+Qp) t/V]} (48)
and
Q
co x4^Q
Case 8: Combination of Cases 2 and 5 (G = 0, (h = 0), and
C = CQ exp (- EQr t/V) (50)
and
-402-
-------
C.-O (51)
Case 9: Combination of Cases 1, 2 and 3 (Ci = G = C = 0, E * 1), and
C = CQ exp [- (Q1+Qf) t/V] (52)
and
Cw = 0 (53)
Continuing with his theoretical study Turk refers to the con-
cept of air exchange defined as the number (N) of air changes per unit
time
N/t = Q/V
or N = Qt/V (54)
Turk recognizes, 1n his discussion of the "well-mixed" tank
theory, the mixing of outdoor air with air already in the chamber may
take place over time intervals sufficiently long so that the premise of
instantaneous mixing becomes Invalid for modeling purposes. He notes that
concentration fall-off rates will then be smaller than the ones which would
result from the ideal instantaneous mixing. A mixing factor as which,
according to Brief [89] ranges between 1/3 to 1/10, is applied to correct
for this. Turks's work has been used in all subsequent studies relating
indoor-outdoor air pollution levels.
-403-
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The "Black-Box" Model
Hunt and others at NBS in an indoor air pollution status
report [318] have developed a methodology called the "black box" model of
a building with forced ventilation. Figure A-2 indicates the major
components of the simulated structure. Equation (55) shows the relation-
ship among the various factors entering into the "black box" model.
f:0r
V "
A
Miter
fQb
v
Figure A-2. Schematic representation of a ventilated enclosed space [318].
dt
Rate of change
of total pollu-
tant with time
ab(l-E)
Rate enter-
ing in fresh
air
Rate gener-
ated in
enclosed
space
QEr
Rate removed
by fiItera-
tion
(55)
Rate removed
by exhaust
-404-
-------
where
Q is the total amount of pollutant in the enclosed space
v is the volume of the enclosed sapce
a is the concentration of pollutant in outside air
b is the volume rate at which outside air is brought into
the space
E is the efficiency of the filters
G is the rate at which pollutant is generated in the enclosed
space
r is the volume rate at which air is recirculated.
Equation (55) is expressed as
$ = A - BQ (56)
where
A = ab(l-E) + G
D _ ER + b
B y
Treating all parameters involved as constants, Hunt performs
a series of straightforward mathematical steps and arrives at the
following solution of Equation (56).
Q = £ (l-e'Bt) + Q0e-Bt (57)
Q = 4 for steady state at t = » (58)
oo [J
Obvious similarities between the Turk and Hunt studies should
be noted. The concept of response time is introduced by the Hunt study.
-405-
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The response time of an enclosed space is the time required for the indoor
concentration of a pollutant to rise from zero to a given fraction of
its steady state level. The response time is given by:
ln (59)
In theory infinite time is required for reaching steady state,
however in practice Q approaches Q in relatively short time. It is of
oo
interest to note that while the outdoor concentration determines the
magnitude of the indoor steady state concentration, 1t does not
determine the time period necessary to reach the steady state. Under
the stated assumptions the response time is a characteristic of the
building only, see Equation (59).
Further investigation of the steady state expression, and
rearrangement of the individual parameters leads to the following
straight line equation:
QCO
-j Ma + N (60)
where the slope
M = gVb is the f1lter1n9 factor, and
o
the intercept N = Er + b is the source-sink factor
The "black box" model has been applied for cases in which
the outside concentration changes vary according to the following
-406-
-------
equation:
a = a, + a0 slnwt (fil)
where
a-j is the average concentration
aQ is the amplitude, and
w is the angular rate of change of the sine
function.
The solution of Equation (52) is
Q = A'(i-e-Bt) + Q e-Bt + Ao'w e-Bt + ° (Bsinwt - wcoswt) (62)
B ° B2 + w2 BZ + w2
where
A' = a^fl-E) + G , and A^ = aQb(l-E)
are the only symbols not previously explained. The authors of this study
point out that the model can be applied to buildings with air conditioning
and without air conditioning, but they however recognize many difficulties
in obtaining infiltration/exfiltration rates for non-air conditioned
structures.
The Li near-Dynamic Model
The linear-dynamic model described in the remaining pages of
this section is the most recent product of an investigation of the
indoor-outdoor pollution problentby Dr. Fredrick H. Shair and his
-407-
-------
research team [561]. Shair investigated relationships between
indoor air pollution energy conservation with the objective of providing
a basis for reducing energy utilized for heating the various California
Institute of Technology campus buildings while minimizing indoor pollution
levels; this was thus a theoretical and experimental (practical) research
undertaking.
The linear-dynamic model, like previous models examined, is a
mass balance flow analysis of a well mixed airborne pollutant. Figure A-3,
shown below, diagrams the model and its component flows:
MAKE-UP AIR
BUILD IMG VOLU.VE V
SURFACE; AREA A =
so'jfjce s
SINK R
CONCrWi RATION Cj
OUTDOOR CO.';Cr N'T RATION C0
f.Xi II.TF(Ain) AIR
MAiiS tlALAf-JCE FOR AIR:
Figure A-3. Schematic diagram of ventilation model [56l] .
(Generally, makeup air and recirculated air both pass through the same filter and intake fan system.)
-408-
-------
In this model the outdoor air, containing an ambient pollutant concentra-
tion enters a building of volume V by three distinct processes: (1) air
penetrates into the enclosure from outside through doors, windows and
cracks at a rate q2; this is the infiltrated air; (2) it enters from
the outside as make-up air via the "breathing outlets" and passes through
a filter at a predetermined rate q ; this is make-up or partially purified
air; and (3) the air is circulated into the structure and reenters via the
same or another filter at a rate q^; this is the recirculated air. The
air exits the building by (1) exfiltration through the same openings as
for infiltration, and (2) exhaust ducts. The pollutant concentrations may
be increased indoors due to internal sources operating at the rate S, and
decreased due to internal sinks operating at rate R; the net rate of
Internal pollution generation is S - R. A factor FQ describes the pol-
lutant cleaning efficiency of the filter in the make-up air stream; it
is
F . Cinlet - Coutlet (63)
0 Cinlet
where
C. , + = the pollutant concentration in the air just prior
inlet to entering the filter
C +1 4. - the pollutant concentration in the air just as
outlet it leayes the f11ter>
The pollutant cleaning efficiency of the filter for the recircu-
lated air stream is characterized by a similarly defined factor FJ.
-409-
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An Infiltration rate for the building is defined by totally stopping the
regulated structure breathing outlets, the remaining air flow into the
building then occurs at the infiltration rate. In practice the infil-
tration rate can be measured in the building by quantifying the rate of
air changes with the help of an inert gas.
The mass balance equation describing the above processes is:
dC-
V-BT = qoco f^o*+ qici (1'Fi) * q2co - < Wq2> ci+ s -R
Previous knowledge of (1) the filter factors and their variations
with time, (2) the infiltration rate of the structure, and (3) the genera-
tion and decay rates due to indoor sources and sinks, respectively, is
required before any practical application of Shair's model is undertaken.
The numerical values of these rates are obtained experimentally for each
enclosure. It is convenient to make a series of parameter changes to
nondimensionalize Equation (64); the new parameters are:
ei = Ci/cref T = qot/V' a = ql/qo' B = q2/qo' Y = KJAJ/qof
6 = 1 +a F] + 8 + Y, e = 1 + 8 - FQ, eQ = CQ/Cref, and o = s/qQCref,
where K. is a decomposition rate on the jth surface with area A. and refers
J J
to the indoor sinks, and C - is a reference concentration chosen for
convenience. The new equation with nondimensional variables is:
de.
3^- + se. = ee0 + a (65)
-410-
-------
with solution
e. - ee"T eT 6dt + e'T f eT adr + ee'T (66)
f eT 60dt + e'T f
5T
where 9. = C- /C ^ and C. the indoor concentration at t=o. Equation (66)
relates the indoor concentration to the outdoor pollutant concentration.
Five time scales enter into the development of this model: the time t-j
relating to the changes in the outdoor concentration, and ST time to
remove the enclosed air by one of the following four processes: (1) make-
up air, (2) recirculated filtered air, (3) infiltrated air, and (4) time
to remove the pollutant by a first-order decomposition (decay) mechanism.
The value t, is either of the same order of magnitude (or smaller) or much
larger than the inverse of the sum of the inverses of the four fir char-
acteristic times. If tj is of the same or smaller magnitude than the
sum, Equation (66) should be used in its totality for ventilation calcu-
lations. If t1 is large with respect to the sum than the last term in
the equation may be neglected. A series of useful approximations can be
formulated and easy analytical solutions can be obtained. The outdoor
pollutant concentrations are made to vary in an approximately sinusoidal
manner in order to investigate the phase differences in the indoor-outdoor
maximum concentrations. CQ is approximated by the expression CQ = Cio +
at over the time t1 since:
"Many cases of practical interest involve an input
function which does not warrant the use of a sophis-
ticated interpolating procedure in order to predict
-411-
-------
the pollutant concentration within a time interval
defined by two successive data points." [561]
This model is the result of a series of theoretical and ex-
perimental steps. It is similar in its basic concept to the other models,
but is more advanced and better validated than other analytical works.
An underlying assumption of this model is the uniformity of
the pollutant concentrations; all gradients are neglected in this study.
Emphasis is placed on the various ventilation rates of the structure.
A previous knowledge of engineering parameters is required to implement
this analysis. A validation study by Shair that followed the formulations
of this model showed a favorable comparison of the theoretical and
experimental results [561].
A.3 THE STATE-OF-THE-ART OF DEFINITION OF MODEL INPUT PARAMETERS
The principal existing indoor-outdoor air pollution models were
discussed, in the previous section, on a model-by-model basis. The present
section will review the state-of-the-art of definitions of the principal
parameters common to most models, these being:
Pollutant strengths.and decay rates
Indoor environment characteristics
Structural characteristics
Human activities
Monitoring constraints.
The discussion which follows is not entirely derived directly
from the scientific literature; it includes some concepts for parameter
-412-
-------
definitions which are now under development by the authors of the
present report.
A.3.1 Pollutant Source Strengths and Decay Rates
The fate or time-history of a pollutant, once It appears
indoors, 1s a complex function of a number of factors denoted by two
generic terms: sources and sinks. Section 3.1 of this report described
some investigations of the emission rates of source-strengths for pol-
lutants generated indoors. The following conclusions emerge when the
literature on indoor pollution source-strengths is viewed from the
numerical modeling point of view:
Experimental technology, Including instrumentation
accuracy and precision, and monitoring design vary
widely. Owing to this variation, model calculations
should be compared with experimental data on a trend-
basis rather than on the absolute magnitude of the
investigated parameter.
Indoor generation rate estimates are subject to ±500
percent or more variation [141]. This large range of
indoor pollution source-strength requires that numerical
investigations be undertaken for average, per unit time,
source strengths as well as for maximum and minimum
indoor generation rates.
The literature research has not produced evidence of
research 1n which combined experimental and analytical
studies were conducted to estimate indoor source
strengths. The use of a detailed tracer experiment
and the "backwards-integration" analytical approach
may provide realistic estimates of the rate of emission
of an indoor source. Details of this approach will be
discussed in Section A.4.
Section 4.0 described previous research into pollutant behavior
inside buildings, including the chemical decay and transformation of some
-413-
-------
pollutants. The chemical properties of pollutants are Important; the
numerical analyst must Investigate all the processes and the relative
Importance of the various Indoor sinks. It 1s appropriate to recall the
characteristic times associated with mechanisms that may be considered
Indoor pollution sinks [561]: (1) a characteristic time to exchange
the air with make-up air; (2) a characteristic time to remove the
pollutant via the recirculation filter; (3) a characteristic time to
exchange the building air with infiltrated air; and (4) a characteristic
time to remove the pollutant via a first-order decomposition mechanism.
The following general conclusion has been reached with respect to the
relative order of the pollutant removing processes: From the model
development point of view the chemical decomposition of the indoor
pollutants 1s slow when it is compared to other processes included
in the mass balance equation which simulates the indoor-outdoor air
/
pollution levels [Shair (1976) private communication]. A direct result
of this conclusion is that in many cases the model does not Include a
sink factor which refers strictly to the chemical pollutant behavior.
Two notes of caution are necessary with respect to the above statement:
(1) this conclusion does not apply to highly reactive pollutants, such
as ozone or other oxidants, and (2) with respect to conservative pol-
lutants, it is a general conclusion in need of more specific investiga-
tions and further validation.
A.3.2 Indoor Environmental Parameters
The indoor environmental parameters, temperature and relative
humidity, are indirect parameters; by this it is meant that they do not
-414-
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explicitly enter Into any of the reviewed Indoor-outdoor air pollution
models but they do affect pollutant decay rates, human activity, and
building occupancy habits, and the operational modes of various Indoor
pollution sources. These two parameters must be Investigated 1n order
to search for correlations between them and the various explicitly stated
Input variables of Indoor-outdoor air pollution models. Work of this
nature has been reported 1n the literature, although not extensively.
References to It are Included 1n Section 4.0 of this document.
A.3.3 Structure Identification Parameters
Another set of Indirect parameters is that of the structure
Identification parameters. Models require that air exchange rates be
parameterized as a function of structure Identification parameters.
Building material descriptions such as density, heat capacity, thickness
of the floors, walls, windows, ceiling; building descriptions such as
area of the zones, height of the ceiling, height of plenum, lighting,
heat systems, equipment operating schedules, type of mechanical system,
and other control parameters constitute a partial 11st of the structure
identification parameters. On the following pages a building information
report format appears which is being used 1n conjunction with field moni-
toring work in an EPA-sponsored indoor air pollution research project now
being performed by GEOMET. It is intended that the information gained
from this report will be utilized in conjunction with a set of measured
indoor and outdoor air pollution concentration levels, meteorological
parameters and building ventilation rates in the formulation of an
improved general indoor-outdoor air pollution model. This report format,
-415-
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which was developed by Hittman Associates, Inc., is included here
because it defines structural parameters which are relevant for model
ing purposes and because it furnishes information for future formu-
lation of an algorithm relating building parameters and ventilation
rates as an input in the indoor-outdoor pollution model.
STRUCTURAL AND ENERGY DATA
for
Indoor-Outdoor Air Pollution Study
Site-
Address
Type of Structure:
One Story
Split Level
Bi-Level
Story and a Half
Two Story
Three Story
Attached
Detached
-4T6-
-------
Height of Building (feet)_ ',_ Height of One Story
Total floor area 1n structure (square feet)
Glass area as percentage of floor area (excluding glass doors)
Are structures oriented so that glass area 1s distributed in
particular direction? yes no
If yes, what 1s the approximate distribution of glass area by sides
of structure?
North % South % East % West %
If glass area 1s distributed 1n no particular direction, assume
structure faces North.
Does structure have basement? Full Half No
Heated? Full Half No
If no basement, what 1s beneath floor:
Concrete slab Crawl space
If crawl space, 1s there Insulation under floor? Yes No
If Yes, type and amount?
If full or partial unheated basement, 1s there Insulation under floor?
Yes No
If Yes, type and amount?
-417-
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Is there an attached, enclosed garage?
Yes
No
Heating System
011
Gas
Distribution System
Air
Steam
Cooling System
Electric
Electric
Water
Other Fuel
1 pipe
District Steam
2 pipe
_Heat Pump
_3 pipe
Solar Assisted
_4 pipe
If electric heat, central or radiant?
If electric cooling, central, or individual units?
Central Individual
Hot water heating fuel is:
oil
gas
district steam
District Chilled
Water
Absorption
Oil
Gas
District Steam
electric
Describe the external color of building walls.
Light park
Number of Exterior Doors (excluding glass doors per structure),
1, 2, 3, 4, , 1 per unit
Door Material
No. of sliding glass doors per structure, 1 per unit
orientation of glass doors - N S E W
area per door sq. ft.
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Do the units have balconies? Yes No
If yes, give dimensions ft. wide x ft. long
Type of Roof - Peak or Gable (height = '), flat, built-up
(high rise)
Exterior Wall Construction - Material and dimension or overall
"R" value
Ext. Wall Ext. Wall
Layer Type 1 Type 2 Roof to Ceiling Party Wall
Windows: Frame material - wood aluminum
Glazing - single, double, triple
Storm windows? Yes No
Exterior dimensions of Building - ft x ft
Sketch of Floor Plan:
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A.3.4 Human Activity Information for Modeling
Human activities Impact upon Indoor air quality through the
ways in which people use building ventilation systems, entrances, and
windows, and through the use of pollutant-generating materials and
equipment Indoors. The frequency and duration of occupancy of various
Indoor spaces 1s an Important factor necessary to adequately determine
Indoor pollutant exposure episodes. This type of Information 1s usually
collected by researchers through subject Interrogation. The literature
of this type of research has been reported 1n Section 6.0, with examples
of the occupancy and activity profiles used to quantify the behavior
of people moving and engaging In various activities within structures.
The reader 1s referred to Section 6.0 of this report for a discussion.
The literature review has revealed that various occupancy
profile sources can be found, but few of these sources Include profiles
of distribution of occupancy within a building. The variation among
occupancy profiles from different sources Indicates the wide range of
occupancy profiles for Individual buildings. Any sampling of buildings
to determine an average occupancy profile 1s likely to show some variation
from any other sampling of the same population of buildings. But all
of the profiles found for any one building type do have the same general
form; and although some variation is present, they are very much alike.
Another important aspect of human activity is represented by
the Information to be gained through daily diary logs of human activity
in a home. An example of such a log follows:
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Daily Activity Log
SITE:
DATE:
1) Did you cook breakfast? From when to when? How many burners were
used?
2) Did you cook lunch? From when to when? How many burners were used?
3) Did you cook dinner? From when to when? How many burners were used?
i
4) Did you have guests? From when to when? If yes, how many?
Between what hours?
5) Did you do special cooking (baking, for example) which took more
cooking time than noted in (1), (2), and (3)?
If yes, when?
6) Did you do any cleaning?
If yes, what kind of cleaning material did you use?
7) Did you or your guests smoke? What type of smoking (cigarette, cigar,
etc.) and for how long?
8) Did you use an air freshener?
If yes, what kind (brand) at what times?
9) Did you use any aerosols?
If yes, what kind (brand) at what times?
10) Did you open the windows?
If yes, between what hours?
11) Did you vacuum?
If yes, from when to when?
12) Did you turn on the range hood fan while cooking?
13) Did you use a fireplace? When?
14) Was there a period of time that nobody was home, what hours?
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A.3.5 Monitoring Constraints on Model Characteristics
The air pollution monitoring networks used to obtain data
for development and validation of models are constrained by the state-
of-the-art. Models use the best available sets of data, but they are
not the Ideal sets. Data used 1n modeling must be considered with
respect to Its reliability; 1t is necessary to know the types of
Instruments used, their detection limits, response times and sensi-
tivity. The location of sampler probes is critical; are the probe sites
representative? The design of the monitoring system Is Important,
Including procedures for calibration and quality assurance. The Importance
of these factors becomes apparent when comparative studies are under-
taken.
The nature of the pollutants Impose constraints on the
modeling approach. For example, a realistic averaging time for par-
ticulates may result in eight-hour samples because no instrumentation
exists to give reliable measurements of particulates gathered 1n shorter
times at the low concentrations prevailing in some non-workplace
environments. This example would Impose an eight-hour time period on
the modeling study of indoor particulates, while one-hour or smaller
time periods would be considered for gaseous pollutants.
A.4 A PROVISIONAL GEOMET DESIGN FOR AN INDOOR AIR POLLUTION MODEL
GEOMET is now engaged, as a part of its current EPA-sponsored
program of indoor air pollution research, in planning for the future
development of an improved indoor air pollution simulation model which
will build upon the existing body of research (just described) and
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which will rely for additional field data and preliminary validation
upon a program of field monitoring of Indoor air pollution and related
parameters which 1s now underway.
A provisional design for major elements of the planned
GEOMET model has been developed. The model 1s built upon the concepts
of the linear-dynamic model of Shalr [561], But the Shalr model and
all other previous modeling studies described In this report have
assumed that there are no air pollution gradients within a structure.
In the GEOMET program it is planned to Introduce the concept of
Interior zones within the building. Each zone may have Its own pollution
concentration level. The concept assumes uniform mixing within each
designated zone but effectively provides a means of describing stepwlse
pollutant concentration gradients within a structure. To make the
assumption of uniform pollutant mixing within each zone a realistic
assumption and to simulate true gradients It will be necessary to have
a large number of zones in each structure, I.e., zones must be
smal1.
Two important parameters of the planned GEOMET modeling effort
are the "breathing" rates, and the efficiency coefficient of the Indoor
pollution control equipment. "Breathing" rate 1s a generic term used
for a total building air change rate; 1t represents the sum of ventila-
tion rate and the 1nfiltrat1on/exf11trat1on rates. Measurement of the
ventilation rate will be critical for model accuracy.
A.5 USE OF TRACER GASES IN MEASUREMENT OF VENTILATION RATES AND
OTHER ASPECTS OF INDOOR AIR POLLUTION MODELS
Development of a zoned indoor pollution model will require the
calculation of ventilation rates through field measurements with a
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tracer gas. To measure the total air change rate of a building a known
amount of an Inert tracer gas, for example, sulfur hexafluoHde (SFg),
1s emitted Into the enclosed space. The concentration of this tracer
1s monitored for a certain time period, and the ventilation rate 1s
obtained from the slope of a semllog plot of the natural logarithm of
the pollutant concentration vs. time. The equation
c c0 . - a *
Indicates that the slope 1s the ventilation rate a. A point of
Importance, for 1t helps validate the a value, 1s Integration of the
concentration-time curve which should produce the originally Introduced
tracer amount; such an approach has been successfully undertaken under
carefully controlled conditions [149].
The air exchange rates of a dwelling can be determined by
an experimental methodology which requires simultaneous continuous and
grab sampling monitoring, there are two approaches:
The three-outlet approach, which provides the skeleton
of the breathing rates of a dwelling
The detailed-comprehensive approach, which monitors
every structural division of a residence (rooms, halls,
closets) and furnishes data for the zone-concept.
The three-outlet approach monitors the tracer 1n three Indoor
locations on a continuous basis for a 12-hour period. The comprehensive
approach 1s a grab sampling technique that requires samples on a half-hourly
-424-
-------
basis for each room and hallway for a twelve-hour period. The three
outlet continuous tracer monitoring approach follows established metho-
dologies which will not be repeated here. The comprehensive approach
1s outlined 1n the following paragraphs.
The tracer concentrations are monitored one time per hour In
every room and hallway of the Investigated dwelling. Assuming that the
tracer 1s SFg, the grab sampling can be done with plastic syringes of
10-30 cc's; the syringes must be carefully marked to Indicate the location
and the time of the sampling. The plastic syringes can be easily closed
and transported from the experimental site to the laboratory for analysis.
In work conducted by Dr. Fredrick Shalr at California Institute of
Technology, 1t has been shown that the SFg concentration Inside the
syringe will not change for two weeks [private communication from
Dr. Fredrick Shalr, 1976] which 1s adequate time for the required
transportation from the field to the laboratory. During the twelve-
hour period of tracer experimentation of the occupants' behavior must
be kept, such a diary will provide data for a correlation between occupancy
habits and 1nf1ltrat1on/exf1ltrat1on and ventilation rates. Structural
and HVAC system data will also be obtained.
This approach, using tracer studies to determine Interior
air flow characteristics combined with other field data, will provide:
(1) the details of the structure's air channels} necessary information
for the formulation of the zone concept; (2) the Influence on each
structural division (rooms, hallway, closet) of brief openings of doors
or windows; (3) the rate of mixing as a function of geographical location
-425-
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within the structure; and (4) the necessary data for an Integration to
estimate, analytically, Indoor-generated pollutant source strengths from
an experimental reading at a certain distance from the source.
Hunt and Burch [317] have reported on their study of "Air
Infiltration Measurements in a Four-Bedroom Townhouse Using Sulfur
Hexafluoride as a Tracer Gas." After providing the structural character-
istics of the unoccupied townhouse they describe Its air distribution
system, which consisted of a duct system leading to the rooms and a
common return located in a hallway. A circulating fan forced air
through the furnace and Into distribution ducts leading to the various
rooms. SFg was introduced into the circulating fan and distributed
through the house. A gas chromatograph was used to measure the tracer
concentrations, this Instrument was calibrated three or four times during
the course of each air exchange measurement against a known SFg/air
mixture concentration. Air samples were taken at specific times and
were analyzed for SFg. Three different sampling methods were used:
Composite samples were collected manually with a hand
pump and a balloon, going from room to room in a pre-
determined order; upstairs and downstairs were con-
sidered two different entities.
Samples were collected through a sampling network con-
sisting of 16 polyethylene tubes of identical length
having a 6mmID. At least one tube extended to each
of the rooms and hallways and converged at a common
point, passing Into a 12 liter/minute diaphragm pump.
Samples were taken from the return air at the entrance
to the main ventilating fan In the central air system.
The authors state that the first two methods are "usually
not practical" for occupied houses; a special check was made to avoid
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tracer entry error by monitoring at strategically chosen locations, near
the reentry duct. They also took simultaneous experimental readings
by using both helium and SFg air exchange to check the possible signi-
ficance of molecular diffusion; helium 1s expected to have six times
the molecular diffusion of SFg. Though the agreement of simultaneous
measurements was not perfect, the difference was not large, see Figure
A-4. The flow through buildings due to the stack effect was calculated
by the following empirical relationship found in the ASHRAE Handbook
of Fundamentals:
Q = 9.4 A rti UQ - t^ (67)
where
Q 1s the air rate in cubic feet per minute
A 1s the free area of Inlets or outlets (assured equal) in
square feet
h is the height from inlets to outlets in feet
t.j is the average temperature of indoor air in height h
tQ is the temperature of outdoor air (F).
If the inlets and outlets are at the same level, h equals
zero, and there is then, of course, no vertical air flow and no stack
effect. From Equation (67) one estimates the infiltration rate in air
changes per hour as follows:
N = 60 Z/V (68)
-427-
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Where V is the volume of the Investigated structure, Figure A-4
Illustrates some of the results of this study.
1.2
IT 10
q
5 0.3
o.
lil
ii O.G
.*
O
o *
0.2
(
1 1 1 1 1
O HAND SAMPLING
A NETWORK SAMPLING
V RETURN SAMPLING
_ ^ A t*f imiAmr^ i ikitr "*
BASED ON Q * S.4AVh (t,-to)
J*S
^^.tf, --"^
% ^^^ 0
^ >>^ °°
/ V ^
' \ 1 1 1 1
D 10 2O 30 40 50 6
.TEMPERATURE DIFFERENCE BETWEEN INSIDE
AND OUTSIDE °F
Figure A-4. Infiltration rate as a function of temperature difference between inside and outside [ 317 ]
Filter efficiency in air cleaning systems affects air flow
rate through the system as well as impacting upon the removal of pollutants,
A preliminary survey of available air filters for the cleaning of venti-
lation air or recirculated air for the conditioning of residential build-
ings, indicates a wide variety of efficiencies and particle holding
characteristics are obtainable. Various operating characteristics of
air filters are required In order to establish a means of rating each
filter. These characteristics include filter efficiency, air flow
-428-
-------
resistance and particle or dust holding capacity. This subject has been
discussed 1n Section 7.0.
A.6 CONCLUSIONS
At the minimum, an indoor-outdoor air pollution model must
provide a framework within which 1t 1s possible to estimate pollutant
concentrations indoors in terms of specifications of corresponding
pollutant characteristics Immediately outside an enclosed space, and
the structural and energy data of the building itself. The reviewed
Indoor-outdoor air pollution models achieve this minimum requirement
for a given structure; further research 1s needed to generalize the
application of the models.
The following conclusions can be drawn from the study of
existing Indoor-outdoor air pollution modeling research.
The fundamental principle involved is straightforward,
(a mass balance equation) and theoretically sound;
it has been used by all researchers who have developed
indoor-outdoor ventilation and air pollution models.
0 All practical applications of the existing models
require a prior knowledge of a rather large number
of coefficients and constants Included in the model
expressions. Extensive field work Is necessary to
obtain these necessary factors.
There are many knowledge gaps: Internal pollution
generation and indoor source strengths must be
studied more extensively; Indoor sinks (decay rates)
need more attention; indoor pollution levels are affected
by the energy conversation measurements, by the Inhabi-
tants' activity factors, by the home structural character-
istics and others; these relations are inadequately known
at present.
-429-
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The most difficult research problem Identified 1n this appraisal
of the literature of Indoor air pollution modeling 1s 1n the effort
required to determine the constants of the basic functional relationship
simulating the Indoor-outdoor air pollution levels. The reviewed models
have avoided this difficulty by considering only one investigated
structure and by experimentally determining these coefficients for a
unique structure. One objective of new modeling effort now being
sponsored by EPA is to formulate a model that may be applied to any
given building under varying conditions. In GEOMET's current work for
EPA toward this goal a series of parameterization procedures will be
undertaken to use, 1n acceptable model input form, data from a current
field study now underway and data from'past field studies found in
literature. The following parameters must be studied and connected
t>
by functional or associative numerical relationship.
Outdoor pollution levels
0 Indoor generation of pollutants
Building permeability (ventilation, infiltration rates)
Meteorological conditions (indoor/outdoor)
Ventilation system capacity
Building identification parameters, Including zones
Energy conservation factors
Indoor pollutant behavior
Human activity factors
Indoor air pollution control instrumentation
-430-
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A model capable of Interrelating these factors, using data
readily obtainable by state-of-the-art monitoring and field survey
technology, and fitted with coefficients of general applicability,
would represent a very substantial advance upon existing modeling
capabilities. This is the objective, perhaps only in part achievable
at present, of work now in progress.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
i. REPORT NO.
EPA-600/4-77-029
3. RECIPIENT'S ACCESSION>NO.
4. TITLE AND SUBTITLE
THE STATUS OF INDOOR AIR POLIIJTION RESEARCH 1976
FINAL REPORT
5. REPORT DATE
May 1977 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Prepared by GEOMET, Incorporated
EPA Project Officer Dr. S. David Shearer, Jr.
8. PERFORMING ORGANIZATION REPORT NO.
GEOMET Report Number EF-547
9. PERFORMING ORGANIZATION NAME AND ADDRESS
GEOMET, Incorporated
15 Firstfield Road
Gaithersburg, Maryland 20760
10. PROGRAM ELEMENT NO.
1AA601
11. CONTRACT/GRANT NO.
Contract Number 68-02-2294
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Monitoring and Support Laboratory RTF , NC
Office of Research and Development
U. S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
Contract Report - Phase I
14. SPONSORING AGENCY CODE
EPA/600/08
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Numerous research projects have examined the occurrences of air pollution in outdoor and workplace environments.
A smaller, newer body of research has examined air pollution in nonworkplace, indoor environments. A new emphasis
on measures to conserve energy in buildings, curbing heat loss through reduced indoor-outdoor air exchange, has
encouraged interest in the relation between indoor and outdoor air quality, building energy conservation, and the
potentials for adverse health effects from indoor air pollution in nonworkplace environments. A review of this b«dy of
research is the subject of this report. The preparation of this report required a comprehensive survey and assessment of
the state-of-the-art of indoor air pollution research described in published literature and unpublished ongoing research.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN E,NDED TERMS
COSATl i-'icld/Group
Air pollution
Monitors
Conservation
Health
Air pollution sources
13B
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
487
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
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