INDOOR-OUTDOOR AIR POLLUTION
RELATIONSHIPS:
A LITERATURE REVIEW
U.S. ENVIRONMENTAL PROTECTION AGENCY
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INDOOR-OUTDOOR
AIR POLLUTION RELATIONSHIPS:
A LITERATURE REVIEW
Ferris B. Benson
John J. Henderson
D. E. Coldwell
ENVIRONMENTAL PROTECTION AGENCY
National Environmental Research Center
Research Triangle Park, North Carolina
August 1972
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The AP series of reports is issued by the Environmental Protection Agency to re-
port the results of scientific and engineering studies, and information of general
interest in the field of air pollution. Information presented in this series includes
coverage of intramural activities involving air pollution research and control tech-
nology and of cooperative programs and studies conducted in conjunction with state
and local agencies, research institutes, and industrial organizations. Copies of
AP reports are available free of charge to Federal employees, current contractors
and grantees, and nonprofit organizations - as supplies permit - from the Air Pol-
lution Technical Information Center, Environmental Protection Agency, Research
Triangle Park, North Carolina 27711 or for the cost indicated on the title page from
the Superintendent of Documents.
Publication No. AP-112
For sale by tho Superintendent o( Documents, U.S. Government Printing Office, Washington, D.C. 20402
11
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PREFACE
The information on which this report was based was compiled over a period of
years by Mr. John J. Henderson, formerly of the Division of Health Effects
Research but presently with the Regional Air Pollution Control Office, Dallas,
Texas, and by Mr. Ferris B. Benson, Bioenvironmental Measurements Branch,
Division of Health Effects Research, National Environmental Research Center
(NERC), Research Triangle Park, North Carolina. Mr. D. E. Caldwell of the
Technical Publications Branch, Information Services Division, Office of Adminis-
tration, Research Triangle Park, North Carolina, organized and tabulated the data
for further analysis and co-authored the review.
The authors wish to express their appreciation to Dr. R. J. M. Horton,
Office of the Director, NERC, for his assistance in all aspects of the report pre-
paration, but especially in locating pertinent information.
ill
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ABSTRACT
Extensive measurements have been and are being made of outdoor pollution.
In contrast, very few data have been gathered on indoor pollution, especially in
view of the importance of the problem. The data that are available are compiled
and analyzed in this report. Based on a review of the literature, it was possible to
infer relationships between indoor and outdoor pollution and to identify factors that
affect these relationships. The relationships identified must be considered tenta-
tive, however, and further research is recommended to determine their validity.
Except for bacteria and, perhaps, for fungus spores, indoor pollution levels
appear to be controlled primarily by outdoor concentrations. Other factors that
influence indoor pollution levels include internal activities and pollutant generation,
atmospheric conditions and natural ventilation, time, location, type of building,
and air conditioning and filtration systems. At present, the best available estimate
of indoor concentrations of particulates and nonreactive gases can be obtained by
assuming them equal to outdoor concentrations. Indoor concentrations of pollen
and reactive gases, expressed as a percentage of outdoor concentrations, decrease
with increasing outdoor concentrations. Bacterial concentrations indoors appear
to be more closely related to the presence and activities of people inside than to
outdoor concentrations.
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CONTENTS
LIST OF FIGURES vii
LIST OF TABLES viii
1. INTRODUCTION „ i
2. RELATIONSHIPS BETWEEN INDOOR AND OUTDOOR POLLUTION
LEVELS 5
GASES 5
Sulfur Dioxide , 5
Carbon Monoxide 7
Carbon Dioxide 7
Summary 8
PARTICULATES 8
VIABLE PARTICLES 12
Spores ...... . 12
Pollen 16
Bacteria 16
Summary 18
3. OTHER FACTORS AFFECTING INDOOR CONCENTRATIONS . ..... 19
INTERNAL ACTIVITIES AND POLLUTANT GENERATION. 19
Gases 19
Particulates 21
Viable Particles 23
Summary 23
ATMOSPHERIC CONDITIONS AND NATURAL VENTILATION .... 24
TIME 26
Gases 26
Particulates 28
Viable Particles 32
LOCATION 34
TYPE OF BUILDING. 36
Carbon Monoxide 36
Particulates 37
Summary 39
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AIR CONDITIONING AND FILTRATION .............. 40
Gases .............. 40
Particulates 41
Viable Particles ..................... 41
Summary 42
4. INSTRUMENTATION AND PROCEDURES 45
5. CONCLUSIONS AND RECOMMENDATIONS 47
CONCLUSIONS 47
Indoor-Outdoor Concentrations 47
Other Factors Affecting Indoor Concentrations 48
Summary 50
RECOMMENDATIONS 50
REFERENCES 53
APPENDIX A. COMPILATION OF INDOOR-OUTDOOR AIR POLLUTION
DATA „ 59
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LIST OF FIGURES
Figure Page
2-1 Indoor Concentrations of Sulfur Dioxide and Carbon Monoxide as
a Function of Outdoor Concentrations 6
2-2 Indoor Particulate Concentrations as a Function of Outdoor Con-
centrations 9
2-3 Indoor Pollen Concentrations as a Function of Outdoor Concentra-
tions, Non-Air-Conditioned Buildings IV
3-1 Carbon Monoxide Concentrations in House with Gas Range and
Furnace and with Attached Garage 21
3-2 Carbon Monoxide Concentrations for House in Hartford,
Connecticut; September 22, 1969 25
3-3 Concentration of Particles in an Apartment in Toyonaka City, Japan,
May 21-22, 1956 „ 29
3-4 Seasonal Variation of Particulate Concentrations and Indoor/Outdoor
Ratios in Hartford, Connecticut 32
3-5 Effect of Type of Building on Indoor/Outdoor Carbon Monoxide
Concentrations 38
3-6 Effect of Type of Building on Indoor/Outdoor Particulate
Concentrations 39
vn
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LIST OF TABLES
Table PaSe
2-1 Indoor Concentrations of Carbon Dioxide for Several Buildings in
Osaka, Japan ........................ 8
2-2 Indoor /Outdoor Concentration Ratios for Spores of the Ten Most
Commonly Occurring Fungi ......... . ........ 13
2-3 Distribution in Indoor and Outdoor Air of Spores of the Ten Most
Commonly Occurring Fungi ..... ... .......... 14
2-4 Composition of Spore Colonies in House Dust .......... 16
3-1 Sulfur Dioxide Concentrations for Two Coal-Heated Houses ... 19
3-2 Carbon Monoxide Concentrations near a Plant with an Open Hearth
Furnace .......................... 20
3-3 Indoor Particulate Distribution by Height for Waking and Sleeping
Periods ...................... .... 22
3-4 Particle Counts Before, During, and After Classes in Schools . . 22
3-5 Variation of Carbon Monoxide Concentrations with Time near
Plant with Blast Furnace ... .......... . ..... 26
3-6 Day/Night Ratios of Carbon Monoxide Concentrations, Hartford,
Connecticut ......................... 27
3-7 Indoor /Outdoor Percentages of Carbon Monoxide, by Day and
Night, Hartford, Connecticut ............. .... 28
3-8 Day/Night Ratios of Particulate Concentrations, Hartford, Connect-
icut ............................ 29
3-9 Day/Night Ratios of Indoor /Outdoor Percentages for Particulate
Concentrations, Hartford, Connecticut ...... . ...... 30
3-10 Day /Night Ratios of Soiling Particulate Concentrations, Hartford,
Connecticut .........................
3-11 Day/Night Ratios of Indoor /Outdoor Percentages for Soiling Par-
ticulate Concentrations, Hartford, Connecticut ......... 31
3-12 Dust Densities for Winter, Spring, and Summer ........ 31
3-13 Day/Night Ratios of Bacterial Concentrations, Toyonaka City,
Japan ........................... 03
3-14 Day/Night Ratios of Indoor /Outdoor Percentages for Bacteria,
Toyonaka City, Japan .................... 33
3-15 Bacterial Count in Japan for Winter, Spring, and Summer .... 34
3-16 Sulfur Dioxide Concentrations in the Vicinity of an Industrial
Plant
Vlll
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Table Page
3-17 Average Carbon Monoxide Concentrations for Several Types
of Buildings, Hartford, Connecticut 37
3-18 Average Particulate Concentrations for Several Types of Build-
ings, Hartford, Connecticut 38
3-19 Effect of Air Conditioners, Filters, and Purifiers on Indoor
Pollen Concentrations and on Indoor/Outdoor Ratios ....... 43
A-l Indoor and Outdoor Concentrations of Sulfur Dioxide 60
A-2 Indoor and Outdoor Concentrations of Carbon Monoxide 61
A-3 Indoor and Outdoor Concentrations of Gaseous Pollutants Other
Than SO2 and CO 62
A-4 Indoor and Outdoor Concentrations of Particulates 63
A-5 Indoor and Outdoor Concentrations of Fungus Spores 65
A-6 Indoor and Outdoor Concentrations of Specific Fungus Spores ... 66
A-7 Fungus Spore Composition of Indoor and Outdoor Samples in
European Studies 69
A-8 Fungus Spore Composition of Indoor and Outdoor Samples in
U.S. Studies 70
A-9 Range and Occurrence of Fungus Spores in Indoor and Outdoor
Samples, U.S. and European Studies 71
A-10 Indoor and Outdoor Pollen Concentrations 72
A-11 Indoor and Outdoor Concentrations of Bacteria 73
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INDOOR-OUTDOOR
AIR POLLUTION RELATIONSHIPS:
A LITERATURE REVIEW
CHAPTER 1. INTRODUCTION
Air pollution is defined in a number of air pollution control laws as" . . .the
presence in the outdoor atmosphere of one or more contaminants, or combinations
thereof, in such quantities and of such duration as may be or tend to be injurious
to human, plant, or animal life or property. ..." Thus, air pollution is legally
defined in terms of outdoor concentrations. The average person, however, spends
about 80 percent of his time indoors, and those who are most susceptible to the
health effects of pollution, the elderly and the chronically ill, spend an even higher
percentage indoors.
Extensive measurements have been and are being made of the presence and
concentrations of many types of pollutants in the outdoor air. In contrast, con-
sidering the importance of the problem, very few data have been gathered on the
presence, concentration, and generation of pollutants in indoor environments and
on the penetration of pollutants from the outdoor environment into buildings. Even
though a large number of publications include some information of application to
the problem of indoor pollution (over 75 publications are specifically cited in this
report), only recently have comprehensive investigations of the problem been
initiated.
It is the purpose of this report to compile the extant but scattered data and
analyze them to determine if relationships can be established between indoor and
outdoor pollution levels and to determine if other factors that influence indoor con-
centrations can be identified.
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All information related to indoor-outdoor pollution relationships that could be
located in published form was reviewed. Pollutant types considered included gases,
particulates, and viable particles (pollen, fungus spores, and bacteria). Building
types included residences, offices, laboratories, schools, hospitals, and public
buildings. Buildings such as factories and manufacturing plants were considered
to constitute a special problem beyond the scope of this study.
The review and analysis presented in the next chapters are highly dependent
1 8
on the results of recently instigated studies in the United States " and on some-
what earlier studies in Japan. ^~14 Some of the data considered, however, were
obtained as early as 1903. The data reviewed are not limited to United States
publications. Significant contributions were culled from Japanese and Russian
publications, and the literature of many other countries is represented.
The publications reviewed are described in an annotated bibliography pre-
pared as a companion document to this report. The bibliography also contains a
number of references not specifically cited in this report. These include referen-
ces that provided useful general background information for the review, but no
specific information or data; foreign-language publications that were not translated
for the review because of the constraints of time and money; and publications
covering highly specific pollutants, such as biological warfare aerosols and radio-
active particles, and buildings with special pollution problems, such as public
garages.
All data of general application to indoor-outdoor pollution relationships are
compiled and tabulated in Appendix A. These data are analyzed in the next chapter
to determine possible general relationships between indoor and outdoor concentra-
tions. In Chapter 3, factors other than outdoor concentrations that may affect the
indoor-outdoor relationships defined in Chapter 2 are examined. In Chapter 4,
the techniques that have been employed in measuring indoor pollution and the pro-
blems associated with such measurements are discussed. Chapter 5 includes a
summary of the major conclusions resulting from this review and suggestions for
further research to define and evaluate indoor-outdoor pollution relationships.
In the discussions that follow, indoor pollution levels are commonly expressed
as a percentage of outdoor levels (indoor/outdoor concentrations x 100). The reader
should keep in mind the fact that a low indoor/outdoor percentage does not
2 INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
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necessarily imply a low indoor concentration. For example, in the relationship
for sulfur dioxide presented in the next chapter, an interior concentration of 10
parts per hundred million (pphm) was found for an outside concentration of 15 pphm
(indoor/outdoor = 67 percent). In another instance, the indoor concentration was
30 pphm when the outdoor concentration was 100 pphm (indoor/outdoor = 30 percent).
Thus the actual indoor concentration at an indoor/outdoor ratio of 30 percent was
much higher than at a ratio of 67 percent. This approach was employed to permit
better definition of indoor pollution as a function of outdoor pollution. The identifi-
cation of relationships between indoor and outdoor pollution would permit the esti-
mation of indoor levels from the outdoor data, which are more abundant.
Introduction
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CHAPTER 2.
RELATIONSHIPS BETWEEN INDOOR AND OUTDOOR POLLUTION LEVELS
GASES
Data related to indoor concentrations of gaseous pollutants are presented in
Tables A-l, A-2, and A-3. ' . The data represent a wide range of studies
conducted for varying purposes under a wide range of conditions. Except for
sulfur dioxide (SC>2) and carbon monoxide (CO), the data are highly limited.
Sulfur Dioxide
Figure 2-1 presents the ratio between indoor and outdoor SO2 concentrations
(expressed as percentage) versus outdoor concentrations. With a few exceptions,
the data follow a consistent pattern, as delineated in the figure. Indoor concentra-
tions approach, or even exceed, outdoor concentrations when outdoor concentra-
tions are low, but drop rather rapidly to about 50 percent of outdoor levels as
outdoor concentrations increase up to about 20 pphm; then they drop more slowly
to a value approaching 30 percent or less with further increases in outdoor levels.
This relationship has been noted in several studies, in which, for the most part,
indoor SC>2 concentrations have been found to be consistently lower than outdoor
concentrations.16'21'24'26
Two factors affecting the lower concentrations of SC>2 indoors have been
identified. First, SC>2 is reactive, and thus tends to be absorbed by •walls and by
interior surfaces and finishes. ' Second, outdoor peak concentrations, which are
sharp and often of relatively short duration, are not fully reflected by indoor con-
centration patterns.
Some reported data on indoor SC>2 concentrations were not included in Table
A-l and Figure 2-1 since mean values were not reported. These data generally
support the relationship noted above, however. Weatherly", 26 reported an aver-
age indoor/outdoor ratio of 60 percent for outdoor concentrations ranging between
9. 6 and 57. 3 pphm for a laboratory in London. For another London laboratory,
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10
OUTDOOR CARBON MONOXIDE CONCENTRATION, ppm
20 30 40
50
60
120
100
§
o
te
o.
cc
O
O
Q
O
80
O 60
O
D
40
20
2 POINTS
400 % @ 0.2 pphm
1600 % @ 0.2 pphm
SULFUR DIOXIDE (SO?)
CARBON MONOXIDE (CO)
57%
at 70
pphm
J
30%
@ 100 pphm
0
10
50
20 30 40
OUTDOOR SULFUR DIOXIDE CONCENTRATION, pphm
Figure 2-1. Indoor concentrations of sulfur dioxide and carbon monoxide as a function of outdoor concentrations.
J
60
reported indoor/outdoor ratios ranging from 25 to less than 100 percent
for indoor concentrations of 3 to 6 pphm and outdoor concentrations of 5 to 17
pphm.
A rather extensive program of SC>2 sampling was carried out in Boston and
Cambridge, Massachusetts, by Arthur D. Little, Inc. , ^' ^ but results were pre-
sented graphically, and average concentrations were not tabulated. (Raw data on
an hourly basis are included in Reference 8. ) For the low levels measured during
the summer - generally between 3. 5 and 5 pphm - indoor and outdoor levels were
nearly equal. When outdoor concentrations rose above 5 pphm, indoor concentra-
tions remained near their normal levels; but when outdoor concentrations fell below
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
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3. 5 pphm, indoor concentrations normally did also. For a period of several days
in a building that housed both offices and laboratories, indoor concentrations were
greater than outdoor concentrations. Outdoor concentrations were on the order of
4 pphm, however, and indoor levels were only about 5 pphm. For the higher SC>2
concentrations measured during the winter, the indoor-outdoor relationship was
generally in accord with that shown in Figure 2-1, i.e. , the difference between
indoor and outdoor concentrations was greater when outdoor concentrations were
higher.
Another rather extensive program of SC>2 sampling was conducted in Germany,
but the results were reported only in general terms. These results indicated that
indoor concentrations could be expected to range from 4 to 28 percent of outdoor
levels for outdoor concentrations greater than 0. 4 milligram per cubic meter
(approximately 15 pphm), but that they might be as high as 80 to 100 percent if
windows were open and a high wind was blowing. '
Carbon Monoxide
Carbon monoxide concentrations, also plotted in Figure 2-1, appear to follow
a pattern similar to that shown for SO2 concentrations. Based on the data plotted,
it would appear that indoor CO concentrations range from 80 to greater than 100
percent for outdoor concentrations below 10 ppm, but range from 60 to 80 percent
for outdoor concentrations above 10 ppm. These conclusions must be viewed with
some suspicion, however. Carbon .monoxide is unreactive, and indoor concentra-
3 4
tions have been expected to approximate those outdoors after a certain lag time. '
It should be noted also that the CO data shown in Figure 2-1 represent only two
studies. All the data for outdoor concentrations below 10 ppm were obtained in
Hartford, Connecticut, and all data for concentrations above 10 ppm were obtained
in Moscow.
A limited amount of data in addition to that presented in Table A-2 and Figure
2-1 is available in the literature. ' ' ' These data are representative of
special conditions, however, and will be discussed later in the report in context.
Carbon Dioxide
As might be expected, data for carbon dioxide (CO2) do not follow the same
pattern as data for other gaseous pollutants. Except for emissions from smoking,
cooking, and heating, the other pollutants are essentially produced outside, and
indoor concentrations can be expected to be lower. Carbon dioxide, in contrast,
Relationships Between Indoor and Outdoor Levels 7
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is produced by people inside, and indoor concentrations can be expected to be
higher. Assuming that outdoor concentrations are normally around 0.03 percent,
concentrations in several types of office buildings were found to range from 1 to
10
over 10 times outdoor levels (Table 2-1). iu According to Ishido, a space of 10 cu-
bic meters (m3) per person and a recirculation rate of 30 m3/hr are required to
maintain CC>2 concentrations below 0.1 percent in rooms where people are doing
office work.
10
Table 2-1.
INDOOR CONCENTRATIONS OF CARBON DIOXIDE FOR SEVERAL
BUILDINGS IN OSAKA, JAPAN10
Type of building
Office building
Old office building
Old office building
New air-conditioned
office building
New air-conditioned
office building
Newer air-conditioned
building
Season
NSa
Winter
Summer
Winter
Summer
NS
Indoor concentration
range, percent
0.06 to 0.32
0.08 to 0.28
0.04 to 0.09
0.06 to 0.23
0.04 to 0.13
0.03 to 0.14
aNS not specified.
Summary
The data available for nitrogen dioxide, carbon bisulfide, hydrogen sulfide,
and total gaseous acids (Table A-3) are insufficient for identifying relationships.
From the data in Tables A-l through A-3, and in Figure 2-1, however, it appears
that indoor concentrations of gaseous pollutants are generally lower than outdoor
concentrations, but by less than 50 percent unless outdoor concentrations are high.
At very low levels of outdoor pollution, inside concentrations sometimes exceed
outdoor concentrations. A definite trend of decreasing indoor/outdoor ratios
with increasing outdoor concentration has been identified for SC>2 as shown in
Figure 2-1. A similar trend for CO is a possibility, but, for the present, it seems
wiser to assume that indoor CO levels will be equal to or only slightly less than
outdoor levels. Concentrations of CO2, since it is produced inside, are normally
higher inside than out.
PARTICULATES
Data related to indoor concentrations of particulates are listed in Table A-4
and plotted in Figure 2-2.2- H-14. 18,21,25.26, 29-39 Data for soiling index are
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
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120
100
80
&
s
§ 60
i-
O
cc
O
O
i 40
20
• HARTFORD
O OTHER
O
O
a. BY WEIGHT
50 100 150 200 250 300
OUTDOOR CONCENTRATION, ug/m3
350
400
450
120
100
80
O
O
I.
40
\'
•*•
O
O
• JAPAN
O OTHER
b. BY PARTICLE COUNT
500 750 1000 1250 1500 1750 2000 2250 2500
OUTDOOR CONCENTRATION, particles/cm3
1
Figure 2-2. Indoor particulate concentrations as a function of outdoor concentrations.
Relationships Between Indoor and Outdoor Levels
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not plotted because the majority of these data represent a narrow range of very
low concentrations, and no patterns can be shown graphically.
The most obvious conclusions that might be drawn from Figure 2-2 are that
indoor/outdoor particulate concentrations by weight generally decrease with in-
creasing outdoor concentration, but that indoor/outdoor particle counts remain
relatively constant at about 80 to 100 percent of outdoor concentrations regardless
of outdoor concentration. These conclusions may well prove to be unfounded, how-
ever. Almost all the data for concentration by weight were obtained in one study
conducted in Hartford, Connecticut, and the data for particle counts, although
based on several studies, were obtained primarily in Japan for the Department of
Home Economics of Osaka City University. 11-14 in both cases, as can be seen in
Figure 2-2, the trends noted above are not supported by the limited amount of data
available from other sources.
Three possible trends in the relationship between indoor and outdoor particu-
late concentrations have been identified in the literature, as summarized, respec-
tively, in the following three paragraphs. The first trend identified appears to be
the best supported.
Ishido and his colleagues concluded, as a result of their studies in Japan, that,
even in relatively air-tight buildings, ' and in schools and hospitals as well as in
small rooms, indoor suspended particulate levels are completely under the
influence of outdoor changes. They further concluded that the generation of dust
by daily activities may have some effect, but that it is of relatively short duration
and is not directly reflected in daily variations in indoor dust concentrations. l^"*4
Although changes in indoor concentrations lag behind outdoor changes and the range
of concentrations is smaller indoors, indoor levels are nearly equal to outdoor
levels if mean values over 24-hour periods are considered.1? These conclusions
are supported by statistical analyses of the results of two studies30' 32 which
indicated that differences in indoor and outdoor concentrations were not significant
at the 5 percent level. A study in Cincinnati indicated that "under normal atmo-
spheric conditions, the main component of suspended matter in the home was drawn
from outside air, while during 'smog1 periods the correspondence of the two
measurements was even closer. "34 A study in Rotterdam indicated that indoor/
outdoor concentrations remained relatively constant at about 80 percent during 24-
hour periods, regardless of outdoor concentrations.21
10 INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
A study in a London office"' lends some support to the relationship indica-
ted by Figure 2-2a, but not at the same concentrations or percentages. Indoor and
outdoor concentrations were found to be about equal up to concentrations of 300
micrograms per cubic meter ((J.g/m ). When outdoor concentrations were above
this level, the concentrations indoors were less than those outdoors; and, the
higher the outside concentrations, the greater the percentage difference. The
lowest indoor/outdoor ratio noted, however, was 78 percent for an outdoor con-
centration of 800 |J.g/m3. It has also been noted that indoor and outdoor levels
showed fair agreement when windows were kept open, but that indoor levels were
sometimes less than half of outdoor levels when windows were closed, particularly
at night. 36
Romagnoli, who concluded that indoor dust content does not seem to reflect
•J rj
the outside dust levels, J' and Kanitz, who attached equal importance to outside
concentrations and to the presence and activities of people inside, 0 must be con-
sidered in the minority. In some instances, however, such as in the crowded
classrooms where Romagnoli obtained his data, the presence and activities of
people inside may be of greater importance than outdoor concentrations.
The data in Figure 2-2 indicate a tendency for at least slightly lower partic-
ulate levels indoors. These data indicate indoor concentrations less than those
outdoors in 42 of 44 instances (95 percent) by weight and 19 of 25 instances (76
percent) by particle count. In three studies that reported comparisons of this type
for individual locations or sampling periods, ratios were 18 to 30 (60 percent), ®
9 to 21 (43 percent), and 16 to 24 (67 percent). Thus, although indoor partic-
ulate concentrations are generally lower than outdoor concentrations, the pattern
is not consistent, and a significant number of instances when indoor concentrations
were higher than those outdoors have been reported.
There is some indication that the composition of indoor particles may differ
from that of outdoor particles. In one study, median particle diameter inside
was found to be 0. 36 micron, compared with 0. 46 micron outside. In an air-
conditioned office building, 99 percent of the particles were smaller than 0. 7
micron, while 89 percent of outdoor particles were smaller than 0.7 micron.
In another study, 85 percent of indoor particles were found to be 1 micron or
smaller, while only 74 percent of those outside were 1 micron or smaller.
Relationships Between Indoor and Outdoor Levels
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The difference in particle size in the latter study, however, was less than 0.2 mi-
cron and was not significant at the 5 percent level. In Hartford, the smaller par-
ticles associated with soiling index were found to penetrate buildings more read-
ily than the larger particles associated with suspended particulate measurements.
In still another study,30 the ash content of the particles was determined.
The ash content of indoor samples ranged from 1. 5 to 38. 0 percent, with a mean
of 13. 3 percent. Ash in outdoor samples ranged from 2.1 to 80 percent, with a
mean of 29.3 percent. This difference, which was highly significant at the 1 per-
cent level, indicates that indoor air contains more organic material than outdoor
air. Higher organic contents for indoor particulates were also noted in the
Hartford study.
In summary, indoor particulate concentrations appear to be generally lower
than outdoor concentrations, especially at high outdoor levels, and the compo-
sition of the particulates inside is different from that outside. As was the case
for carbon monoxide, however, it seems best in light of the data presently avail-
able to assume indoor concentrations approximately equal to outside concentrations.
VIABLE PARTICLES
Not all particulate pollution is inanimate. Bacterial, fungal, and plant
spores (including pollen), though "naturally, " endogenously generated, are con-
sidered to be pollutants from a health effects standpoint (mold and pollen aller-
gies), for purposes of indoor air quality control (air conditioning), when present
in inordinate amounts, or when present because of human activity.
Spores
Indoor and outdoor concentrations of total fungal spores are presented in
Table A-5. Of the 21 indoor/outdoor ratios tabulated, 3 are noted to be ex-
ceptionally low (data for houses in Cardiff, Wales),57 and 3 to be exceptionally high
(data from Spain and data from Sweden49 for homes with poor hygienic condi-
tions). Fourteen of the remaining 15 are below 90 percent. Consideration of
those values below 90 percent indicates that averages are around 40 percent (mean
41 percent; median 38 percent; mode 30 to 40 percent). Thus it appears that in-
door spore concentratiorfs generally range from 15 to 90 percent and average around
40 p.ercent of outdoor concentrations.
12
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
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The wide disparities among measuring and reporting procedures in the
studies summarized in Table A-5 preclude analysis of indoor/outdoor ratios
as a function of varying outdoor concentrations.
Consideration of the composition of the spores found indoors and outdoors
indicates that indoor populations are not directly controlled by outdoor popula-
tions. Indoor and outdoor concentration ratios of the ten most commonly reported
types of spores are summarized in Tables 2-2 and 2-3. Detailed data on which
Table 2-2. INDOOR/OUTDOOR CONCENTRATION RATIOS FOR SPORES OF THE TEN
MOST COMMONLY OCCURRING FUNGIa
Fungus
Penici Ilium
Cladosporium
Aspergillus
Hormodendron
Mycelia sterilia0
Mucor
Pull ul aria
Yeasts
Alternaria
Phoma
Range of
indoor/outdoor
ratios, %
29 to 567
0.3 to 26
24 to 138b
18 to 20
24 to 30
90 to 300d
4 to 50
27
0 to 44
3 to 75
Studies in which
ratio reported was:
<100 %
4
7
4
2
2
1
4
1
6
4
>100 %
4
0
2
0
0
4
0
0
0
0
Total
studies
8
7
6
2
2
5
4
1
6
4
aData from Spain^l excluded since indoor/outdoor ratios were much higher
than general data trend.
bRange does not include an instance in which Aspergillus was found indoors
but not outdoors; ratio would approach infinity.
cThe majority of these organisms are in the family Deutromycetes.
^Range does not include two instances in which Mucor was found indoors but
not outdoors; ratio would approach infinity.
these summaries are based are presented in Tables A-6 to A-9. Table 2-2 com-
pares the spores in terms of indoor/outdoor percentage and Table 2-3 in terms of
percentage of total colonies. It should be kept in mind that the data in Table 2-3
do not allow direct comparisons between indoor and outdoor concentrations;
rather, the data indicate the relative distribution of each type of spore in the to-
tal population, either indoors or out. These tables indicate that the spore com-
position of inside air samples is quite different from that of outside samples.
Penicillium is the most common spore found both indoors and out. Indoor
concentrations have been reported to be significantly less than those outdoors (29
Relationships Between Indoor and Outdoor Levels
13
-------
Table 2-3. DISTRIBUTION IN INDOOR AND OUTDOOR AIR OF SPORES
OF THE TEN MOST COMMONLY OCCURING FUNGI
Fungus
Penici Ilium
Cladosporium
Aspergillus
Honnodendron
Mycelia sterilia
Mucor
Pullularia
Yeasts
/Slternaria
Phoma
Distribution in samples
analyzed, percent
Indoor
15.1 to 73.3
15.8 to 35.9
0.4 to 28.6
12 to 28
0.1 to 27.1
0.6 to 15.6
1.9 to 10
7.3 to 13.2
0 to 2.1
0.3 to 1.1
Outdoor
60 to 69.0
37.2 to 69.0
0 to 23.2
44.0 to 68
0.6 to 17.5
0 to 1.0
5.7 to 18
3.6 to 17.6
0.6 to 7.5
0.5 to 2.9
Locations
(Total = 10)
Indoor
10
6
10
3
4
9
5
4
6
4
Outdoor
10
6
S
3
4
5
5
4
8
4
Relative magnitude
of indoor and
outdoor percent of
total colonies
Indoors > outdoors
in 9 of 10 cases
Outdoors > indoors
in all cases
reported
Indoors > outdoors
in 8 of the 10
cases
Outdoors » in-
doors in all 3
cases
Outdoors > indoors
in 3 of 4 cases
Indoors > outdoors
in 8 of 9 cases
Outdoors > indoors
in all 5 cases
Outdoors > indoors
in 3 of 4 cases
Outdoors > indoors
in 8 of 9 cases
Outdoors > indoors
in 3 of 4 cases
Remarks
Found both indoors and outdoors
at all locations
Present indoors, absent out-
doors in 1 case
Present indoors, absent out-
doors in 2 cases
Present indoors, absent out-
doors in 2 cases; reverse
in 1.
to 76 percent) in half the studies and significantly greater (172 to 567 percent) in
the other half. Considering indoor and outdoor populations separately, Penicillium
generally constitutes a higher percentage of indoor fungus populations than of out-
door populations (Table 2-3).
Aspergillus is the next most common spore found, especially indoors.
Although concentrations are generally lower indoors than out, Aspergillus is gen-
erally a more commonly occurring member of the indoor population. In at least
one of the ten studies reported, Aspergillus was found to be present indoors but
absent outdoors.
Cladosporium, while not occurring as frequently as Aspergillus, often con-
stitutes a higher percentage of the population, especially outdoors, in those cases
where it has been identified. Indoor/outdoor ratios are quite low, ranging from
0. 3 to 26 percent, and Cladosporium is invariable a more important member of the
outdoor population than of the indoor population, though it has been reported in one
case to constitute over one-third of the spores inside. 5^
Hormodendron is also often an important component of indoor spore popula-
tions, but like Caldosporium, and to an even more marked degree, it is more pre-
valent in outdoor populations than indoor populations and indoor/outdoor ratios are
14
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
uniformly low (12 to 28 percent). Mycelia sterilia shows similar trends, though
not so marked, and the indoor/outdoor ratios are slightly higher (24 to 30 percent),
Mucor is the only one of the ten most common spores that consistently
yields indoor/outdoor ratios greater than 100 percent. It is also more prevalent
in indoor samples than in outdoor samples.
The remaining four commonly found spores constitute a higher percentage of
the outdoor population than the indoor population in most instances. Indoor/out-
door ratios, however, tend to be somewhat higher than those for the molds pre-
viously discussed.
In summary, Penicillium, Aspergillus, and Mucor constitute a higher per-
centage of indoor samples than of outdoor samples. The remaining seven of the
ten most commonly found fungus spores are more prevalent in outdoor samples.
Except for these three fungi, examination of Tables 2-2 and A-6 indicates that in-
door/outdoor ratios of spores are generally below the average (40 percent) indi-
cated for total spores. The same holds true for the less common fungi listed in
Table A-6, except for Oospora, Monilia, Rhizopus, and Aleurisma.
Although a few exceptions can be found in Tables A-6 through A-9 the same
spores are normally found indoors and outdoors. Several investigators have con-
cluded from this fact and from the assumption that relatively few spores are pro-
duced inside and released into the air that the most important source of airborne
spores in normal clean, dry houses is the outside air. ' However, differences
in spore distribution in air samples indicate that indoor concentrations are not
simply and directly related to outdoor concentrations. It is possible that different
spores are transported indoors at different rates, but it is also possible that the
growth and multiplication of these spores inside (especially those of Penicillium
and Mucor) have a greater influence than has been assumed.
A limited amount of data is available on spore populations in house dust
(Table 2-4), as opposed to airborne spores, which are discussed above. In the
two locations studied, fewer genera of fungi were found in house dust than in air.
The samples were made up exclusively of five of the most commonly found spores,
and Penicillium was by far the most predominant genus. Aspergillus and Mucor
were more abundant in dust than in either indoor or outdoor air in Spain. ->1
Relationships Between Indoor and Outdoor Levels 15
-------
Table 2-4. COMPOSITION OF SPORE COLONIES IN HOUSE DUST
Fungus
Penicillium
Cladosporium
Aspergillus
Mucor
Alternaria
Other genera
Percentage of total colonies
Lexington.
Kentucky"
Summer
48.7
0
35.2
0
16.1
0
Uinter
49.6
0
35.9
0
14.5
0
Spain52
Madrid
87.1
3.3
3.9
3.8
1.9
0
Coast
84.4
4.7
2.6
7.9
0.4
0
Aspergillus was also found to be more abundant in house dust than in indoor or
outdoor air in Kentucky. ^
Pollen
Indoor and outdoor pollen concentrations are presented in Table A-10. 43> 57, 59-65
Most data on pollen concentrations have been gathered as part of evaluations of air
conditioners and will be discussed in Chapter 3.
The data for non-air-conditioned buildings from Table A-8 are plotted in Fig-
ure 2-3 in terms of outdoor concentration versus indoor/outdoor ratio. The four
data points for which outdoor concentrations were greater than 100 grains/m3 were
excluded to allow plotting on a more convenient scale. To facilitate comparison
between concentrations in grains per cubic meter and number per sample, the med-
ians were plotted coincident with each other.
A pattern of decreasing indoor/outdoor ratios with increasing outdoor concen-
tration is indicated by the data bands in the figure. Consideration of data above 50
grains/m3 in the figure and above 100 grains/m3 in Table A-8 shows that the rela-
tion is probably not linear above about 50 grains/m3, but is asymptotic, approach-
ing a limit between 1 and 5 percent for outdoor concentrations above 100 grains/m3.
Thus it appears that indoor concentrations will vary from 85 to 100 percent of
outdoor concentrations for low levels to 1 to 20 percent at high levels.
Bacteria
Data related to indoor and outdoor concentrations of bacteria are presented in
Table A-ll. 12, 14,43,66 Indoor/outdoor ratiog ^.^ ^ ^ ^^ ^ Q
16
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
100
10
20
OUTDOOR CONCENTRATION, grains/m3 (by weight)
30 40 50 60 70 80
90
100
0 grains/m3
A No. pollen grains/sample
MEDIAN
50 pollen grains/sample
55 grains/m3 (by weight)
u_
8
o
cc
O
O
Q
20
30 40 50 60 70 80
OUTDOOR CONCENTRATION, no. pollen grains/sample
90
100
Figure 2-3. Indoor pollen concentrations as a function of outdoor concentrations, non-air-conditioned buildings.
Japan, are exceptionally high compared to the other data, and these values have
been excluded in the following analysis. The remaining indoor/outdoor ratios in
the table range from 62 to 273 percent, and half of the ratios are greater than 100
percent. A great disparity is noted between data obtained in Japan and in the United
States, however, perhaps because the Japanese data are for total bacteria while
most of the U.S. data are for streptococci and total "microbes" (which includes
spores as well as bacteria). Indoor/outdoor ratios based on the Japanese data
range from 62 to 225 percent, and only 38 percent of the values are greater than
100 percent. The range for the U.S. data is 75 to 273 percent, and 67 percent of
the values are greater than 100 percent.
Relationships Between Indoor and Outdoor Levels
17
-------
As with the data on spores, the disparities among measuring and reporting
procedures preclude analysis of indoor/outdoor ratios as a function of varying
outdoor concentrations. The consensus of the investigators, however, is that in-
door bacterial counts do not reflect fluctuations in the outdoor air. >14> Dust
density and bacterial counts indoors reportedly show different tendencies, but the
data are insufficient for proving them unrelated. " The influence of living condi-
tions and daily activities on changes in indoor bacterial count is considered relative
ly great. 12
Summary
Available data on indoor pollen concentrations indicate a trend of decreasing
indoor/outdoor ratios with increasing outdoor concentrations (Figure 2-3). Indoor
bacterial concentrations do not appear to be directly related to outdoor concentra-
tions. Several investigators have reported that the most important source of air-
borne spores in clean, dry houses is the outside air. ' Consideration of the
composition of most indoor and outdoor spore populations does not support this
hypothesis, however.
18 INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
CHAPTER 3.
OTHER FACTORS AFFECTING INDOOR CONCENTRATIONS
INTERNAL ACTIVITIES AND POLLUTANT GENERATION
It has been a tacit assumption in the previous section, as in most of the pub-
lications consulted, that the primary source of interior pollution is the outside air.
However, a number of sources of pollutants exist inside buildings, notably heating,
cooking, and smoking. In addition, activities - such as sweeping and dusting, dress
ing, and drying clothes - that entrain dust can affect interior concentrations of sus-
pended particulate and airborne spores as well as the rate of diffusion of gaseous
pollutants. In addition, the nature and types of interior furnishings and finishes
can affect the rate of adsorption of reactive gases. These effects on interior
pollutant concentrations are discussed below.
Gases
Sulfur Dioxide - Interior generation of SC>2 is probably limited to faulty heating
systems burning oil or coal. Biersteker et al. reported that indoor SC>2 con-
centrations were not generally affected to a significant extent by the heating meth-
od used. However, in one 30-year-old home presumed to have a faulty heater, in-
door concentrations averaged 3.8 times the outdoor levels. Table 3-1 shows a
comparison of SO-, concentrations for new and old coal-heated houses in Hartford.
The exceptionally high indoor concentrations for the old coal-heated house are pre-
sumed to be caused by a faulty heating system. Indoor concentrations at this house
were found to be unrelated to outdoor concentrations; peak values were related in-
stead to the stoking periods of the furnace. Indoor concentrations at the new
Table 3-1. SULFUR DIOXIDE CONCENTRATIONS FOR TWO COAL-HEATED HOUSES4
Type of building
New house
Old house
Concentration, pphm
Indoor
5
78
Outdoor
14
10
Indoor/outdoor, %
36
780
19
-------
coal-heated house were much lower than at the old house, even though outdoor con-
3 4
centrations were slightly higher at the new house. '
Indoor SO2 concentrations are reduced by adsorption. According to Chamber-
lain, walls and ceilings should provide a perfect sink for SO2. Thus the rate of
adsorption should be controlled by the rate of diffusion across the boundary layer
to the surface, and vigorous circulation, which would decrease boundary -layer
resistance, should cause increased reductions in SC>2 concentration. " ' Wilson
found that removal of SO2 from indoor air was limited by the properties of interior
surfaces and only slightly by transport to the surfaces. The ceiling (fiberboard
with eggshell paint) •was found to be effective in removing SO2. The floor (lac-
quered cork), walls (painted with emulsion paint), and treated wood surfaces were
not. "Stirring" the air was found to reduce concentrations by 10 to 40 percent,
24
with the most reduction effected at higher concentrations.
Carbon Monoxide - Carbon monoxide is generated indoors by combustion (smoking,
heating, cooking). The effect of combustion can be seen in the data from Russia
in Table 3-2. Indoor concentrations in the natural-gas-equipped home 100 meters
from the plant were higher than those in a home without natural gas located closer
to the plant. 22
Table 3-2. CARBON MONOXIDE CONCENTRATIONS NEAR A PLANT
WITH AN OPEN HEARTH FURNACE22
Distance from plant,
meters
50
TOO
250
500
Concentration, ppm
Indoor
11.6
16.3
9.0
7.6
Outdoor
17.8
16.5
14.9
12.8
Indoor/outdoor,
%
65
99
60
59
According to Yocum et al. (1971), gas heating systems do not appear to
affect indoor CO concentrations, but gas stoves and attached garages do. (It seems
reasonable to assume that gas stoves and garages are also a significant source of
indoor nitrogen dioxide, but no data were found from which the magnitude of this
effect could be evaluated.) The effects of stoves and garages on indoor CO concen-
trations can be seen in Figure 3-1, which shows the CO concentrations in a house
in Hartford having a gas range and an attached garage. The family room is between
20
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
CAR BEING PUT IN GARAGE
CAR BEING TAKEN FROM GARAGE
KITCHEN
__._. FAMILY ROOM
— •— OUTSIDE
1200 1700 2200 I 1300 800 1300 1800 2300 I 400 900 1400
MAR 5 I MAR 6 ' MAR 7
TIME, hours
Figure 3-1. Carbon monoxide concentrations in house with gas range and furnace and with attached garage.3
the kitchen and the garage. For this house, CO concentrations are generally much
higher than and unrelated to outdoor levels. Peak concentrations in the kitchen
correspond to the periods when meals are being cooked, and concentrations in the
family room generally follow those in the kitchen rather than those outside. For
two periods in the record, when the car was being put into or taken out of the
attached garage, the emissions from the garage are the controlling influence on
both the family room and kitchen concentrations.
Particulates
Particulates are also generated by combustion (heating, cooking, smoking).
Smoking has been found to significantly increase particulate concentrations in-
doors. 21> 68 According to Lefcoe and Inculet, smoking just one cigar raised par-
ticle counts by a factor of 10 to 100. Elevated counts persisted for a period of 1 to
3 hours. 68 Yocom et al. (1971) note that the higher concentration of organic par-
ticles indoors may result in part from interior generation of pollutants from
cooking or smoking, although the fact that smaller organic particles penetrate
more readily than larger inorganic particles is also partly responsible for the
difference.
Other Factors Affecting Indoor Concentrations
21
-------
Particles that are present inside are resuspended and/or kept in suspension
by the activities of the people inside. Seisaburo et al. reported particulate con-
centrations at different heights during waking and sleeping periods. These meas-
urements (Table 3-3) indicate that particles are distributed rather uniformly from
floor to ceiling because of activities of people during the day, but that during the
night they tend to settle and become concentrated near the floor. Table 3-4 shows
particle counts in Italian schools before, during, and after classes. Counts were
much higher during classes than before in two of the four cases, presumably be-
^'
cause of the presence and activities of the students. "" There was also an increase
in particle size from a mean of 0.5 micron before class to 1.2 microns during
class. The measurements made after class indicate that concentrations do not
drop rapidly after activities have ceased. 37 This conclusion is supported by the
data of Lefcoe and Inculet, which indicate that high particle counts resulting from
/ Q
cleaning and dusting persist for a period of at least several hours.
Table 3-3. INDOOR PARTICULATE DISTRIBUTION
BY HEIGHT FOR WAKING AND SLEEPING PERIODS14
Height above
floor,
cm
40
100
150
210
Concentration, particles/cm3
Waking hours
676
629
636
669
Sleeping hours
664
640
587
538
Table 3-4. PARTICLE COUNTS BEFORE, DURING,
AND AFTER CLASSES IN SCHOOLS37
Location of
school
Urban
Surburban
residential
Surburban
industrial
Rural
Period
Before
348
100
180
449
During
347
360
421
392
After
410
315
420
490
'-'Measurements were made at set times and do not necessarily indicate peak con-
centrations. Thus higher values measured after class in two instances do not indi-
cate a continuing increase in concentration.
22
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
A number of investigators have concluded that indoor generation and entrain-
ment of particles have a significant effect on indoor-outdoor relationships. In an
office with an air filtration system that reduced interior concentrations to 24 per-
cent of outside levels, the amount of dust generated in a room was found to be pro-
portional to the number of people in the room. 42 An equation was developed for this
relationship:
M=(0.72n + 1) x 1CT3
where: m = the amount of dust generated, m^/sec
n - number of people
Based on limited measurements for air-conditioned office buildings in Hart-
ford, it was concluded that internal generation of suspended and soiling particulates
was a significant factor in the estimation of interior concentrations. For these
buildings, the ratio of internal generation to exterior concentration was estimated
to range from 0 to 0. 6 for indoor/outdoor ratios of 30 to 116 percent (the method of
estimating these ratios is not specified). ° Internal generation may also contribute
to the varying indoor/outdoor ratios and to the indoor/outdoor ratios greater than
100 percent in the Hartford study. 2)
Viable Particles
As pointed out previously, indoor bacterial concentrations appear to be more
closely related to indoor living conditions and activities than to outdoor concentra-
tions. 12-14 po]jen) in contrast, is almost completely dependent on outdoor con-
centrations, as would be expected. As stated in Chapter 2, the importance of
internal generation of spores is not clearly established. Maunsell found, however,
that activities such as cleaning and dusting cause spores to be entrained in the air.
The resulting increase in entrained spores was mainly in Penicillium, Cladospo-
rium, Pullularia, and yeasts. Spores of larger sizes, which were absent in
undisturbed air, were found to be present after dust was raised. **°
Summary
The indoor generation of SC>2 is not normally an important consideration.
Significant exceptions occur, however, when faulty oil- or coal-burning heating
systems are encountered. Carbon monoxide is generated by smoking, cooking,
and heating. Although gas furnaces or heaters are probably not significant sources
Other Factors Affecting Indoor Concentrations 23
-------
of indoor CO, gas ranges apparently are. Attached garages are also a significant
source.
Particulates can also be generated indoors from combustion (heating, cooking,
smoking). Smoking, in particular, has been definitely identified as a significant
source of particulates indoors. Interior generation may account for some of the
scatter in particulate concentration data and may at least partially explain indoor/
outdoor ratios greater than 100 percent. Indoor activities seem to enhance entrain-
ment of particles already present indoors.
Indoor concentrations of bacteria appear to be highly dependent on indoor liv-
ing conditions and activities, but pollen concentrations are almost completely de-
pendent on outdoor concentrations. The importance of internal generation of spores
is not clearly established, but, as with other particles, internal activities can
play an important role in the entrainment of spores found indoors.
Sulfur dioxide (and probably other reactive gases as well) is removed from
interior air by adsorption, the rate of which is dependent primarily on the pro-
perties of the interior surfaces and only slightly on the rate of transport to the
surfaces.
ATMOSPHERIC CONDITIONS AND NATURAL VENTILATION
The importance of atmospheric conditions and natural ventilation was reco-
nized in a study in Cincinnati that revealed large differences in domestic concen-
trations over short distances in the city, depending on window ventilation, on the
proximity of buildings to pollution sources, on wind direction, and on thermal in-
versions. ^5 The way in which these factors can interact to influence indoor-
outdoor pollution relationships can be seen in the following example from the study
in Hartford.2. 3
Simultaneous CO samples were taken inside the dining room and on the out-
side of a house in Hartford. Sampling for 1 day is shown in Figure 3-2. On the
evening illustrated, outside concentrations increased rather rapidly to about 12
ppm because of a light wind from a nearby interstate highway. Indoor concentra-
tions remained around 5 ppm, about equal to the outdoor concentration before it
increased. Because the windows and doors of the house were closed and there was
relatively little influx of air, interior concentrations reacted much more slowly to
24 INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
I 20
O
8
10
1900
2100
TIME, hours
2300
Figure 3-2. Carbon monoxide concentrations for house in Hartford, Connecticut; September 22, 1969.
the change in wind direction than outdoor concentrations did. After 2 hours, out-
door concentrations had increased to about 16 ppm, but indoor concentrations were
still significantly lower at 10 ppm. At this time, the wind direction changed,
causing outside concentrations to drop rapidly to about 3 ppm. Inside concentra-
tions remained high, however, and required 2. 5 hours to return to the low outside
ambient level. Thus, over a 5-hour period, indoor concentrations ranged from
much lower to much higher than outdoor levels (indoor/outdoor ratios ranged from
about 40 to more than 300 percent). ' If either windows or doors had been even
partially open or if a stronger wind had been blowing directly at the windows,
resulting in greater natural ventilation, interior concentrations would probably
? 7
have more nearly reflected those outdoors. ^ '
As mentioned, several studies conducted in Japan have led to the conclusion
that indoor particulate concentrations are not affected by natural ventilation but
n ] A
are controlled entirely by outside concentrations. 7" Other investigators, how-
ever, have noted a significant effect from natural ventilation. Studies in Cincinnati
indicated that indoor and outdoor levels were in fair agreement when windows were
open but that indoor concentrations were sometimes less than half of outdoor con-
centrations when windows were closed. Average indoor concentrations were found
to be roughly 15 percent higher with windows open than with windows closed. 36
Results of the Hartford study mentioned above also support the contention that nat-
ural ventilation affects indoor particulate levels. A seasonal decrease was noted
in the indoor/outdoor percentage from summer to winter, and was hypothesized to
be the result of shutting up buildings for the winter.2 It was also noted that par-
ticulate levels were lower in public buildings than in homes, which can be explain-
ed by a lower air infiltration per volume for the public buildings.
Other Factors Affecting Indoor Concentrations
25
-------
Indoor pollen concentrations were found to be closely associated with both wind
speed and window opening. ^2 When windows were closed, indoor/outdoor ratios
remained relatively constant at approximately 20 percent for wind speeds up to 8
miles per hour (mph). For higher wind speeds, there was a nearly linear increase
in indoor/outdoor ratios up to 97 percent at 15 mph. When windows were open,
penetration of pollen was quite different, but the amount of opening apparently made
little difference.
TIME
Figure 3-2 and the related discussion show how inside concentrations and the
relation between indoor and outdoor concentrations can vary with time. Indoor and
outdoor concentrations of nonviable and viable particles, as well as of gases, have
been found to vary on diurnal and seasonal bases, and the relationship between in-
door and outdoor concentrations has also been found to vary in some cases. The
time-related variations in indoor pollution levels that can be inferred from the
literature are discussed in the following sections.
Gases
Simultaneous study of atmospheric and indoor air for 24 hours for Russian
homes in the vicinity of a plant with a blast furnace showed parallel changes in CO
concentrations, as indicated in Table 3-5. Similar diurnal patterns for carbon
monoxide have been reported for American homes, that is, high concentrations in
the late night and early morning hours, low concentrations later in the morning
(between 7 a.m. and noon), and high concentrations in the afternoon and evening. '
The fact that the higher indoor/outdoor ratios correspond to the higher outdoor
concentrations seems surprising at first, but this may result from a difference in
Table 3-5. VARIATION OF CARBON MONOXIDE CONCENTRATIONS
WITH TIME NEAR PLANT WITH BLAST FURNACE22
Time, hr
0600
1000
1400
1800
2300
Concentral
Indoor
21.8
3.1
18.7
9.3
24.9
;ion, ppm
Outdoor
21.8
6.2
28.0
21.8
24.9
Indoor/outdoor,
%
100
50
67
43
100
26
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
response time between indoor and outdoor levels as noted in the instance shown in
Figure 3-2. The data do illustrate, however, that the indoor-outdoor relationship
varies with time.
Day and night concentrations of carbon monoxide inside and outside a num-
ber of buildings were measured in Hartford, Connecticut, during the summer,
fall, and winter (Table A-2). To better illustrate the diurnal patterns indicated
by these data, ratios of the concentrations during the day to those during the
night are given in Table 3-6.
Table 3-6. DAY/NIGHT RATIOS OF CARBON MONOXIDE CONCENTRATIONS,
HARTFORD, CONNECTICUT2
Building
Library
City Hall
100 CP
250 CP
Blinn St.
Carroll Rd.
Day/night ratio
Summer
Inside
1.49
1.52
1.18
1.07
0.76
0.78
Outside
1.72
1.72
0.91
1.05
0.80
0.76
Fall
Inside
1.05
1.14
1 .44
1.25
0.91
1.09
Outside
1.30
1.30
1.36
1.38
0.95
1.23
Winter
Inside
1.72
1.74
1 .18
0.97
0.98
0.93
Outside
2.09
2.02
1.26
1.76
0.98
0.92
The day/night ratios indicate that concentrations both inside and outside are
higher during the day, except at the Blinn Street home for all three seasons and,
at the Carroll Roadhome during the summer and winter. The day/night ratios
are lower indoors than out; that is, there is less difference between day and night
concentrations indoors than out. Notable exceptions to this trend occur at the
office buildings at 100 Constitution Plaza (CP). A seasonal effect on the diurnal
pattern can also be inferred from the data in Table 3-6. In almost all cases,
there is less difference between day and night concentrations in the summer than
in the winter.
Indoor/outdoor ratios from the Hartford study are listed on day/night and
seasonal bases in Table 3-7. With few exceptions, the ratios are lower during
the day, corresponding to the higher concentrations noted above. Again, the no-
table exceptions to this trend are the data for summer and fall at 100 CP, for which
concentrations were lower and indoor/outdoor ratios were higher during the day.
Other Factors Affecting Indoor Concentrations
27
-------
Table 3-7. INDOOR/OUTDOOR PERCENTAGES OF CARBON MONOXIDE,
BY DAY AND NIGHT, HARTFORD, CONNECTICUT2
Building
Library
City Hall
100 CP
250 CP
Blinn St.
Carroll Rd.
Indoor/outdoor, %
Summer
Day
87
89
131
105
102
104
Night
100
102
100
102
107
102
Fall
Day
78
89
132
96
103
96
Night
96
101
125
104
108
108
Winter
Day
84
80
113
76
107
112
Night
101
93
121
96
108
112
Day/night ratio
. for indoor/outdoor
i
h
Summer
0.87
0.87
1.31
1.03
0.96
1.02
Fall
0.81
0.88
1.05
0.92
0.96
0.89
Winter
0.83
0.86
1.07
0.79
0.99
1.00
A definite time lag has been noted between indoor and outdoor changes in
concentrations of CO, as can be seen in Figure 3-2. In the instance shown, which
represents a relatively tight house with doors and windows shut, the lag time a-
mounted to 2. 5 hours, and indoor concentrations exceeded outdoor concentra-
tions during that period. Measurements of indoor and outdoor concentrations
of total gaseous acid have indicated lag times of up to 2 hours
16
Particulates
Figure 3-3 shows the diurnal pattern obtained during the summer for a Jap-
anese apartment. ^ The pattern should be fairly typical for the Japanese studies
because similar patterns were found throughout the year and indoor and outdoor
12-14
patterns were generally found to be almost identical. The pattern may also
be grossly applicable to the United States. It has been noted that daytime levels
are higher than night levels, and the major peak at around 8 a.m. has been iden-
tified.18'36
A slight lag time can be seen for the indoor concentrations in Figure 3-3,
and it is reported that the lag time at night is even more apparent during the win-
14
ter. The effect of the lag time in the example illustrated is relatively minor, but
it does result in indoor levels higher than outdoor levels twice during the period
covered - "at about 1800 hours and from 2300 to 0100 hours. " Lag times, some-
times amounting to an hour or more, have been reported in other instances, and
indoor curves may show fewer sharp peaks than outdoor curves. ^> ^6
28
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
3000
1200
1500
1800
2100
0300
0600
0900
2400
TIME, hours
Figure 3-3. Concentration of particles in an apartment in Toyonaka City, Japan, May 21-22,1956.^
Measurements of daytime and nighttime particulate concentrations, similar
to those presented above for carbon monoxide, were also taken as part of the Hart-
ford study, and the resulting day/night ratios are listed in Table 3-8. ^ Day/night
ratios are greater than 1 except for two values that are nearly equal to 1. These
values indicate that daytime concentrations of particulates are higher than night-
time levels by as much as 100 percent. For the offices and public buildings, in-
door day/night ratios are lower than outdoor day/night ratios in the summer and
Table 3-8. DAY/NIGHT RATIOS OF PARTICULATE CONCENTRATIONS, HARTFORD, CONNECTICUT2
1200
Building
Library
City Hall
100 CP
250 CP
Blinn St.
Carroll Rd.
Day/night ratio
Summer
Indoor
1.53
1.59
1.09
0.94
1.25
1.62
Outdoor
1.61
1 .96
1.12
1.14
1.21
1.13
Fall
Indoor
^ 1.30
1 .64
1.33
1 .65
1.20
2.00
Outdoor
1.50
1.41
1.26
1.43
1 .29
1.28
Winter
Indoor
1.49
1.70
0.98
1.87
1 .40
1.60
Outdoor
2.24
1.94
1 .53
1.89
1.33
1.21
Other Factors Affecting Indoor Concentrations
29
-------
winter, indicating that there is less difference between day and night concentra-
tions inside than out. For the houses, there is a greater difference between day-
time and nighttime concentration inside than outside except, perhaps, during the
fall. The ratios generally increase from summer to winter, indicating that there
is more variation in concentrations, both inside and outside, in the winter than in
the fall and more variation in the fall than in the summer.
Indoor/outdoor percentages for the Hartford study are listed on day/night
and seasonal bases in Table 3-9. For the offices and public buildings, the per-
centages are slightly less during the day in summer and winter, reflecting the
higher daytime concentrations noted above. For one of the houses, day and night
percentages were nearly equal throughout the year; for the other, daytime per-
centages were much higher than nighttime percentages.
Table 3-9. DAY/NIGHT RATIOS OF INDOOR/OUTDOOR PERCENTAGES FOR PARTICIPATE
CONCENTRATIONS, HARTFORD, CONNECTICUT2
Building
Library
City Hall
100 CP
250 CP
Blinn St.
Carroll Rd.
Indoor/outdoor, %
Summer
Day
50
51
48
45
87
115
Night
52
63
49
55
86
84
Fall
Day
38
62
75
58
56
97
Night
44
53
71
50
61
62
Winter
Day
16
27
31
33
43
51
Night
26
30
48
33
41
39
Day/night ratio for
indoor/outdoor %
Summer
0.96
0.81
0.96
0.82
1.01
1.37
Fall
0.86
1.17
1.05
1.16
0.92
1.56
Winter
0.62
0.90
0.64
1.00
1.05
1 .30
Considering soiling particulate values in Tables 3-10 and 3-11, as opposed
to the suspended particulate data in Tables 3-8 and 3-9, daytime and nighttime
levels appear to be roughly the same, with no consistent differences between the
two values. This difference in behavior between suspended and soiling particu-
lates is probably the result of size differences; the smaller soiling particles tend
to stay suspended at night whereas the larger particles contributing to the day-
time suspended particulate measurement tend to settle out at night.
Indoor and outdoor particulate concentrations were determined on a seasonal
basis in two Japanese studies ' and in the Hartford study mentioned above.
Results of the Japanese studies are summarized in Table 3-12. The data indicate
30
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
Table 3-10. DAY/NIGHT RATIOS OF SOILING PARTICULATE CONCENTRATIONS,
HARTFORD, CONNECTICUT2
Building
Library
City Hall
100 CP
250 CP
Blinn St.
Carroll Rd.
Day/night ratio
Summer
Indoor
1 .36
1.33
0.87
0.81
0.87
0.91
Outdoor
1.35
1.37
0.84
0.89
0.83
0.84
Fall
Indoor
1.03
1.15
1.00
1.05
0.97
1.08
Outdoor
1.12
1.14
1.12
1.12
0.94
0.95
Winter
Indoor
1.21
1 .20
1.03
1.20
0.89
0.90
Outdoor
1.18
1 .18
1 .08
1.12
0.80
0.81
Table 3-11. DAY/NIGHT RATIOS OF INDOOR/OUTDOOR PERCENTAGES FOR SOILING
PARTICULATE CONCENTRATIONS, HARTFORD, CONNECTICUT2
Building
Library
City Hall
100 CP
250 CP
Blinn St.
Carroll Rd.
Indoor/outdoor, %
Summer
Day
81
98
87
57
89
119
Night
81
100
83
62
85
110
Fall
Day
92
115
69
79
88
80
Night
94
114
79
84
89
67
Winter
Day
50
94
85
58
82
93
Night
49
93
89
55
74
83
Day/night ratio for
indoor/outdoor %
Summer
1.00
0.98
1.05
0.92
1.05
1.08
Fall
0.98
1.01
0.87
0.94
0.99
1 .19
Winter
1.02
1.01
0.96
1.05
1.10
1 .12
Table 3-12. DUST DENSITIES FOR WINTER, SPRING, AND SUMMER, JAPAN12'14
(Particles/cm^)
Location
Osaka
Toyonaka
Living room
Bedroom
November
Indoor
1,839
1,654
Outdoor
1,897
2,133
2,133
Indoor/
outdoor,
86
78
March
Indoor
1 ,287
1,602
1,497
Outdoor
1,528
1,801
1 ,801
Indoor/
outdoor,
%
84
89
83
May
Indoor
978
931
1,091
Outdoor
1,047
1,129
1,129
Indoor/
outdoor,
%
91
82
96
June
Indoor
738
670
726
Outdoor
752
703
703
Indoor/
outdoor,
*
98
95
103
a fairly regular decrease in indoor and outdoor concentrations and a correspond-
ing increase in indoor/outdoor ratio from winter to summer.
Some seasonal trends indicated by the Hartford data have been identified
above as they relate to diurnal patterns. The seasonal variation in concentration
and indoor/outdoor ratio can be seen in Figure 3-4, which shows the area
Other Factors Affecting Indoor Concentrations
31
-------
53
a.
ce
O
O
a
I—
O
oc
O
§
100
350
400
200 250 300
CONCENTRATION,pg/m3
Figure 3-4. Seasonal variation of paniculate concentrations and indoor/outdoor ratios in Hartford, Connecticut.2
450
occupied by the data for each season on a plot of outdoor concentration versus in-
door/outdoor ratio, and which indicates a similar trend toward seasonal decrease
in concentration and corresponding increase in indoor/outdoor percentage as
found in the Japanese studies. Figure 3-4 also indicates that the range of outdoor
concentrations is much greater during the winter, while the range of indoor/outdoor
ratios is greater during the summer and fall.
Viable Particles
Spores - Indoor and outdoor spore concentrations on a monthly basis have been
reported for Tucson, Arizona, and Galveston, Texas. For these areas, how-
ever, the data revealed no seasonal variations in either concentration or indoor/
outdoor ratio except for Pullularia, 53 which was found to be more abundant from
November to February.
In Copenhagen, Denmark, concentrations of many of the common spores were
noted to show seasonal variations. The seasons of peak concentrations were as
listed on the following page.
32
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
Hormodendron - Late May to mid-October
Pullularia - Mid-September to mid-October
Alternaria - August to September
Phoma - March to October
Penicillium - None
In Lexington, Kentucky, Wallace found higher indoor and outdoor spore con-
centrations during the summer but higher indoor/outdoor ratios during the winter.52
Bacterial - In Japan, bacterial concentrations both indoors and outdoors are
reported to be low from late night to early morning but high during waking hours,
especially during the afternoon and evening.14 Analysis of the data from the Japan-
ese study on a day/night basis yields the data in Tables 3-13 and 3-14. These data
indicate that outdoor bacterial concentrations are from 2 to 9 times higher during
the day than during the night (Table 3-13). Indoor concentrations were also higher
during the day, but not as markedly so; factors for the living room were from about
1 to 7 and those for the bedroom, excluding November, were about 1 to 1. 5. In
November, the concentrations in the bedroom were significantly greater at night
than during the day. Indoor/outdoor percentages were generally lower during the
day, and for the bedroom they were generally much lower (Table 3-14).
Table 3-13. DAY/NIGHT RATIOS OF BACTERIAL
CONCENTRATIONS, TOYONAKA CITY, JAPAN14
Location
Living room
Bedroom
Outside
Day/night ratio
November
0.94
0.37
2.00
March
6.82
1.54
8.70
May
3.88
1.04
4.80
June
3.77
1.51
3.67
Table 3-14. DAY/NIGHT RATIOS OF INDOOR/OUTDOOR PERCENTAGES FOR BACTERIA,
TOYONAKA CITY, JAPAN14
Location
Living room
Bedroom
Indoor/outdoor, %
November
Day
161
228
Night
344
1240
March
Day
94
122
Night
119
680
May
Day
80
70
Night
99
323
June
Day
66
74
Night
64
180
Day/night ratio for
indoor/outdoor %
November
0.47
0.18
March
0.79
0.18
May
0.81
0.21
June
1 .03
0.41
Other Factors Affecting Indoor Concentrations
33
-------
The day/night differences in indoor concentrations are thought to be the result
of activities of people inside rather than of outdoor concentrations. This explains
the lower day/night difference for the bedroom, •which is occupied at night while the
living room is not
14
On a seasonal basis, there is less day/night difference in concentrations but
greater day/night difference in indoor/outdoor ratios in the winter than in the
spring or summer. Further seasonal trends can be inferred from the data in Table
3-15. These data indicate that concentrations both indoors and outdoors generally
increase from winter to summer. Summer concentrations up to 10 times winter
levels have been reported. ^
Table 3-15. BACTERIAL COUNT IN JAPAN FOR WINTER, SPRING, AND SUMMER12>14
Location
Osaka
Apartment
House
Toyonaka
Living-
room
Bedroom
October-November
Indoor
count
27
71
8.7
12.3
Outdoor
count
16
6
5.4
5.4
Indoor/
outdoor,
%
169
1183
161
228
March
Indoor
count
21.1
27.6
Outdoor
count
22.6
22.6
Indoor/
outdoor,
%
-
-
94
122
May-June
Indoor
count
28
-
35.2
32.8
Outdoor
count
32
-
45.8
45.8
Indoor/
outdoor,
%
87
-
77
72
LOCATION
Examination of the data in Tables A-l to A-ll reveals differences in indoor
pollutant concentrations and indoor/outdoor ratios on national, regional, and local
levels. For instance, indoor concentrations of gaseous pollutants, specifically
SC>2 and CO, ' ' are exceptionally high in Russia compared with those reported
in other studies, resulting perhaps from some aspect of the construction of Russian
homes that makes it easier for gases to diffuse into them. The exceptionally low
indoor/outdoor ratios for particulates reported in Italy and the difference in bac-
terial concentrations between the United States and Japan have already been men-
tioned. Also worthy of note are the differences in concentrations and composition
of spore samples in Tables A-5 to A-9. Exceptionally high concentrations have
been observed, for instance, in the coastal regions of both Spain and Texas, 45,51
34
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
with exceptionally high indoor/outdoor ratios reported for Spain. Exceptionally
low concentrations characterize Arizona.
The type of area considered, that is, urban, industrial, suburban, or rural,
has a great effect on the concentrations encountered, primarily because of the re-
lative proximity of these types of areas to various sources of pollutants. As might
be expected, concentrations of particulates, and probably also of gases, are higher
in urban and industrial areas than in nonindustrial suburbs. ' An areal study
of fungus spore concentrations in Orebro, Sweden, revealed no differences in
spore content, either qualitatively or quantitatively, from the city to a distance
49
of 6 miles outside the city. Fungus spore concentrations may often be higher
in rural areas than in urban or suburban areas, however, because of the presence
49 52
of cattle barns, storage bins, etc. '
The distance of buildings from local specific sources of pollutants plays an
important role in the concentrations found inside the buildings. As expected, in-
door concentrations generally become lower with increasing distance from the
source. '' ' In addition to such sources as industrial plants that affect a
relatively large area, buildings in a much smaller area may be greatly affected
by pollutants such as those generated in garages and filling stations. CO concen-
trations in a dwelling 18 meters from a filling station, for instance, were found
to be as high as 23 ppm and to average only about 8 percent less than those near the
gas pump itself.
To a large extent, the effects of location discussed above pertain to outdoor
as well as indoor pollution levels and could be predicted on the basis of indoor-
outdoor pollution relationships such as those presented in Chapter 2 if such re-
lationships have been established and if local outdoor concentrations are known.
Consider, for instance, the data in Table 3-16 for SO2 concentrations in the vicinity
of an industrial plant. *9 in this instance, maximum concentrations outdoors de-
creased with distance from the plant while indoor concentrations, at this level of
pollution, remained relatively constant, so that indoor concentrations as a per-
centage of outdoor concentrations increased. This trend is still apparent for the
much lower concentrations, both indoors and outdoors, in the area beyond the in-
fluence of the plant. The patterns identified for these data and the levels of the
indoor/outdoor ratios are in good agreement with the relationship delineated for
SO2 in Figure 2-1.
Other Factors Affecting Indoor Concentrations 35
-------
Table 3-16. SULFUR DIOXIDE CONCENTRATIONS IN THE VICINITY
OF AN INDUSTRIAL PLANT19
Distance from plant,
meters
200 to 300
800 to 1000
Beyond influence of
plant
Concentration, ppm
Indoor
0.3
0.3
0.1
Outdoor
1.0
0.6
0.15
Indoor/outdoor,
%
30
50
67
Even within the same building, pollution levels may not be the same in
different locations. Unless they are mixed by inside activity or natural ventila-
tion, particles and some gaseous pollutants (for example, SG>2) may be higher near
the outside walls, especially at openings such as windows and doors, than in the
interior of the building. ' Concentrations of CO and CO2 have been found to be
higher in the upper stories of buildings. ' " Particulate concentracions, in con-
trast, may be higher in the lower stories, while oxides of nitrogen were found to
29
be evenly distributed. In some cases, internally generated pollutants, such as
CO emitted from gas ranges or attached garages, can cause locally high concen-
trations in certain areas of a building (Figure 3-1). 3 At certain times, especially
at night, dust density may vary significantly with height within the same room
(Table 3-3). 14
TYPE OF BUILDING
It seems logical to assume that indoor-outdoor pollution relationships would
be different for different types of buildings, 2> 69 but only a very limited amount
of comparable data is available from which to evaluate the effects of building type.
Carbon Monoxide
Carbon monoxide concentrations were measured in pairs of houses, office
buildings, and public buildings in Hartford.2 As discussed in the next section,
abnormally high indoor/outdoor ratios were measured at an office at 100 Constitu-
tional Plaza (CP) because of the way in which the air conditioner was operated.
Discounting these values, average indoor/outdoor ratios for the houses were about
105 percent; for the remaining office, about 95 percent; and for the public buildings,
about 90 percent (Table 3-17). However, outdoor concentrations were generally
lower in the vicinity of the homes than at the office and the public buildings. Thus
36
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
Table 3-17. AVERAGE CARBON MONOXIDE CONCENTRATIONS FOR SEVERAL
TYPES OF BUILDINGS, HARTFORD CONNECTICUT2
Building
Library
City Hall
Office, 100 CP
Office, 250 CP
House, Blinn
St.
House, Carroll
Rd.
Mean concentration, ppm
Indoor
3.84
3.78
3.21
3.18
2.84
2.56
Outdoor
4.35
4.21
2.69
3.33
2.68
2.44
Indoor/outdoor,
%
88
90
119
96
106
105
it is difficult to determine if the differences in indoor/outdoor ratios are related to
building type or to differences in pollution levels.
Figure 3-5 is a plot of the individual CO data from the Hartford study for the
range of outdoor concentrations common to all three building types. Within this
range (1. 5 to 3. 5 ppm), data for all building types are concentrated between indoor/
outdoor values of 100 and 110 percent, but values for the houses tend to be some-
what higher than those for the office and the public buildings.
Particulates
Particulate concentrations were also measured for the buildings in the Hart-
fort study (Table 3-18). Average indoor/outdoor ratios for the houses were around
65 percent; for the office, around 45 percent; and for the public buildings, around
35 percent. Again, however, outdoor pollution levels were lower in the vicinity of
the houses.
Figure 3-6 is a plot of the data for the range of common outdoor concentra-
tions. A limited amount of data from Whitby et al. 38 which can be plotted in the
same form is included for comparison. Outdoor concentrations for the homes
fall between about 50 and 125 |o.g/m3. Data for the offices and public buildings
for this level of pollution generally fall within the data scatter band for the
houses, but are concentrated in the lower portion of the band.
Presuming the outdoor concentrations to be similar, additional comparisons
of this type can be made from the data reported in References 30, 32, and 33.
Other Factors Affecting Indoor Concentrations
37
-------
120
« 110
0)
a
cc
O
O
O
s
O
a
1 100
90
• HOUSES
A OFFICES
• PUBLIC BUILDINGS
1.5 2.0 2.5 3.0
OUTDOOR CONCENTRATION, ppm
Figure 3-5. Effect of type of building on indoor/outdoor carbon monoxide concentrations.'
3.5
Table 3-18. AVERAGE PARTICULATE CONCENTRATIONS FOR SEVERAL TYPES
OF BUILDINGS, HARTFORD CONNECTICUT2
Building
Library
City Hall
Office, 100 CP
Office, 250 CP
House, Blinn St.
House, Carroll Rd.
Mean concentration,
ug/m3
Indoor
45
66
39
45
52
54
Outdoor
189
159
81
104
86
75
Indoor/outdoor, %
26
42
48
43
60
72
Reference 30 reports indoor ranges of 60 to 539 M.g/m3 for houses and 95 to 232
M-g/m for offices and public buildings. These data support the trend noted for
o
Figure 3-6. References 32 and 33 report ranges of 50 to 1230 particles/cm for
38
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
oc
O
120
100
80
60
40
20
YOCOM et al.2 WHITBY et al.38
HOUSES 9 Q
O OFFICES A A
PUBLIC BUILDINGS •
O
A A
/
25 50 75 100 125 150
OUTDOOR CONCENTRATION, ug/m3
175
200
Figure 3-6. Effect of type of building on indoor/outdoor participate concentrations.
houses and 141 to 1880 particles/cm3 for offices and public buildings. In this in-
stance, lower concentrations are reported for houses, but the ranges are still
similar.
Summary
Based on the limited CO and particulate data available (primarily from
Yocum et al. 1971), 2 it appears that indoor-outdoor pollution relationships are not
greatly different for the pollutants, building types, and ranges of outdoor concen-
trations for which comparable data are available. These data are limited, how-
ever, to CO concentrations between 1. 5 and 3. 5 ppm and, primarily, to particu-
late concentrations between 50 and 125 |ag/m3. For these pollutants at these
concentrations, pollution levels inside houses appear to be slightly higher than
those inside offices and public buildings when similar outdoor concentrations pre-
vail.
Other Factors Affecting Indoor Concentrations
39
-------
AIR CONDITIONING AND FILTRATION
Air-conditioning engineers are confident that air-conditioning systems can be
designed, built, and operated to remove air pollutants so that indoor air in build-
ings and vehicles will be continuously comfortable and free from the stress effects
of air pollution. 70 It has been alleged, however, that "in contrast to what most
people comfortably assume, much of the pollution of the outdoor air enters our
buildings directly through the air conditioning equipment as supplied and installed
today, " and the data with which to refute this charge have yet to be gathered. It
has been noted instead that the current employment of air conditioning is largely
dictated by the economics of heating and cooling with little regard for changes in
indoor air quality and how it is affected by outside pollutant levels, by air-condi-
tioning system parameters, and by internal pollutant generation. * The data avail-
able in the current literature, reviewed in the following sections, may shed some
light on these conflicting allegations.
Gases
A recent study in Boston, Massachusetts, indicated that SC>2 concentrations
were reduced to 60 percent of outside levels simply by bringing the air inside and
that further reductions were not effected by air-conditioning systems unless the
systems included water sprays on the cooling coils. This study also revealed that
ozone concentrations indoors were not generally affected by air conditioning. Air-
conditioning systems with electrostatic precipitators actually caused a slight in-
crease in ozone concentrations, but never enough to be of concern.
Carbon monoxide, being unreactive, is not effectively removed by air-
conditioning. 5> 70 Substantiation for this statement can be seen in Figure 3-5
and Table 3-17. The two office buildings in the Hartford study were air conditioned,
but indoor/outdoor ratios were consistently near 100 percent for the office at 250
CP, and Figure 3-4 shows that there was little difference between that office and
the non-air-conditioned houses and public buildings investigated for the range of
common outdoor levels. Indoor/outdoor percentages for the office at 100 CP were
consistently higher than for either the other office or the non-air-conditioned
buildings.
O
The higher indoor/outdoor ratios for the office at 100 CP are thought to be
directly related to the air-conditioning system and its method of operation. "Stale"
40 INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
air trapped in the building during the overnight shutdown was purged each morning
with "fresh" air drawn from the outside. This "fresh" air, however, was drawn
from near street level during the time of the morning peak traffic period. The
dilution of this initial "charge" of CO provided by the 10 percent make-up air used
during the remainder of the day was apparently not sufficient to reduce the indoor
concentrations to the vicinity of the outdoor levels. *
Participates
The available literature indicates that air-conditioning systems can signif-
icantly reduce indoor particulate concentrations when efficient filters are em-
ployed. An air-conditioning system that maintained a positive interior pressure
was found to reduce indoor concentrations to 24 percent of outdoor levels. This
system employed two filters with high dust-removal efficiency. Electrical dust
collectors have also been noted to be highly effective in eliminating indoor sus-
pended particulate matter. 9 in the Boston study, significant reductions were noted
for a building with a central air-conditioning system having, in succession, an
electrostatic precipitator, a roll screen backing filter, water spray, and cooling
coils.
Yocom et al. (1971) concluded that the roughing filters normally used in air-
conditioning systems are also at least moderately effective in removing particulates.
This conclusion is based on the fact that indoor/outdoor percentages for the two
air-conditioned offices sampled in the Hartford study averaged less than 50 percent.
However, when the data are examined for the range of common outdoor concentra-
tions as in Figure 3-6, indoor/outdoor ratios are not found to be reduced when com-
pared with the non-air-conditioned public buildings nor even consistently reduced
when compared with the houses. Thus, it is not clear whether the apparent reduc-
tion at the offices was a result of the air-conditioning system or was, in fact, a
result of higher outdoor pollution levels. Significant reductions in indoor particu-
late levels for the Boston study were found only for the air-conditioning system
described above. In five other air-conditioned buildings, indoor-outdoor relation-
7 8
ships were about what one would expect for non-air-conditioned buildings. '
Viable Particles
Pollen appears to be the only pollutant which is unequivocally reported to be
reduced by air conditioning. Comparative concentrations for air-conditioned and
Other Factors Affecting Indoor Concentrations 41
-------
non-air-conditioned buildings are presented in Table 3-19. These data indicate
that air conditioning significantly improves indoor pollen concentrations. Indoor/
outdoor ratios for air-conditioned rooms or buildings range from 0. 2 to 2 percent,
whereas those for non-air-conditioned rooms or buildings in companion tests range
from 6 to 68 percent. Some types of air filtration and purification devices were
found to be effective in reducing pollen, °*» " ' °5 but the device evaluated by
Spiegelman et al. °® actually appeared to increase indoor pollen concentrations. In
conjunction with an air conditioner, neither the standard air-conditioner filter
nor the special filter evaluated by Speigelman and Friedman59 was found to improve
indoor pollen concentrations more than the air conditioner alone.
Concentrations of bacteria and spores may also be lower in air-conditioned
buildings, but the data are highly limited and inconclusive. In one study, mold
and bacteria in an air-conditioned room were found to be only 9 percent of those
in a non-air-conditioned room with windows open. "^ But in another study by
the same authors, mold counts ranged from 0 to 20 colonies/dish in a non-air-
conditioned house and from 0 to 25 colonies per dish in an air-conditioned house,
43
while bacteria counts in both houses ranged from 0 to 45 colonies/dish.
Summary
The data available in the literature appear to support the conclusion drawn
from the Boston study: i. e. , the improvement in air quality obtained with air
conditioning is dependent on the type of air cleaning equipment incorporated in the
system; the more sophisticated (and expensive) the equipment, the better the job.
Carbon monoxide, nitric oxide, and light hydrocarbons are difficult to remove
without extensive pretreatment of the intake air. ™ Sulfur dioxide is not removed by
standard air-conditioner components unless they include water sprays. Particu-
late concentrations may be reduced slightly by the roughing filters commonly used
in air conditioners, but more efficient filters must be used to obtain significant re-
ductions. Pollen, in contrast to other pollutants, is practically eliminated by
air conditioning, even without the standard roughing filters normally employed.
Although they are not generally employed in the air-conditioning systems
currently in use, air filtration and purification devices that could significantly re-
duce the indoor concentrations of most pollutants are available. Evaluations of
the efficiency, application, and cost of those components are properly the subject
of a separate report and are not covered here. Holcombe and Kalika^ and Parnell71
present such evaluations. In addition, Kalika et al. * include suggestions concern-
ing the design and operation of air-conditioning systems to reduce indoor pollution.
42 INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
o
s
-------
CHAPTER 4.
INSTRUMENTATION AND PROCEDURES
A general discussion of air pollution measurement techniques is not within the
scope of this report. Discussions of techniques and methods are presented, how-
ever, in References 71 through 74.
Measurement of pollution indoors presents problems that are not encountered
in outdoor measurements. For instance, noisy air samplers, such as the standard
high volume sampler, are not acceptable inside buildings or near residences.2
In addition, the high flow rate of such instruments can affect the results obtained
by modifying the ventilation rate of the room being sampled. 2. 30
Particle size distributions are especially important for indoor-outdoor mea-
surements. As with outdoor pollution, particle size is important because it is re-
lated to sedimentation, soiling, and health effects. 2'71 In addition, as discussed
in Chapter 2, it appears that particles of different sizes may penetrate buildings
at different rates.
Yocum et al. (1971)2 have described a portable, self-contained instrument
package developed especially for indoor/outdoor sampling for particulates and
gases. Some modifications have been made to their system in order to overcome
operational difficulties experienced in early testing and to make possible the deter-
mination of particle size distribution. Reference 75 describes the gas analysis
equipment used on submarines. This equipment should be effective and compact
and could possibly be employed in indoor pollution measurements. Reference 16
describes a small sequence sampler for determining indoor sulfur dioxide concen-
trations. A tape sampler for determining particulate concentrations is described
in Reference 41, and Reference 76 describes methods for determining size distri-
butions as well as concentrations with this type of sampler. Reference 48 includes
a discussion of the comparative limitation of sedimentation and the advantages of
impaction for obtaining samples of airborne viable particles.
The review of literature revealed many shortcomings in the methods that have
been used for obtaining, analyzing, and presenting indoor-outdoor pollution data.
These shortcomings resulted in part from a lack of suitable instrumentation at the
45
-------
time some of the studies were conducted, but to a larger extent they resulted from a
lack of basic knowledge of indoor-outdoor pollution relationships and the factors that
affect these relationships. The data obtained were sufficient, however, to define
possible trends and identify the factors that probably affect the relationships. Based
on the information gathered in this review, recommendations concerning the tech-
niques to be employed in future studies are offered in Chapter 5.
46 INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
CHAPTER 5.
CONCLUSIONS AND RECOMMENDATIONS
CONCLUSIONS
Although indoor-outdoor pollution measurements have been presented in a large
number of references, examination of Tables A-l to A-9 reveals that the amount of
reliable and readily comparable data must still be considered highly limited. Thus,
the conclusions resulting from this review must be regarded as merely tentative.
Indoor-Outdoor Concentrations
Except for bacteria and, perhaps, for fungus spores, indoor pollution levels
appear to be controlled primarily by outdoor concentrations.
Under normal circumstances, the best available estimate for indoor concentra-
tions of particulates and CO (and probably other nonreactive gases as well) can be
obtained by presuming them equal to outdoor concentrations. It is possible that
indoor concentrations of these pollutants are lower than outdoor levels when outdoor
concentrations are high, but the available data do not definitely establish this rela-
tionship.
A fairly •well established relationship of decreasing indoor/outdoor concentra-
tion ratios with increasing outdoor concentrations of SO2 has been identified as
shown in Figure 2-1. This relationship may also be generally applicable for other
reactive gases, but no data are available with which to support this supposition or
with which to evaluate the amount of decrease in relation to the degree of reactivity.
Indoor pollen counts, as a percentage of outdoor counts, also appear to become
lower with increasing outdoor concentrations (Figure 2-3) but this relationship is
not as well substantiated as that for SO2-
Indoor bacterial concentrations have been found to be more closely related to
the presence and activities of people inside than to outdoor concentrations.
Some investigators have concluded that the major source of airborne spores in
normal dry, clean houses is the outdoor air. Differences in the composition of
indoor and outdoor spore populations reported in a number of the publications re-
viewed do not appear to support this contention, however.
47
-------
Other Factors Affecting Indoor Concentrations
Although outdoor concentrations exert a controlling influence on indoor con-
centrations in most situations, a number of other factors have been identified as
affecting, or have been hypothesized to affect, the indoor-outdoor relationship.
These factors include internal activities and pollutant generation, atmospheric
conditions and natural ventilation, time, location, air conditioning and filtration,
and type of building. The effects of these factors must be considered if accurate
estimates and meaningful measurements of indoor concentrations are to be made.
Internal Activities and Pollutant Generation - Pollutants, including CO, SC>2, and
particulates, can be generated by interior activities that involve combustion; e. g.
smoking, cooking, heating. In addition, activities of people inside play a large
part in the entrainment and distribution of pollutants. Internal generation is sus-
pected to be responsible for a great deal of the scatter in reported results and for
some measured indoor concentrations that •were higher than outdoor concentrations.
No quantitative measurements of internal generation have been presented however.
Atmospheric Conditions and Natural Ventilation - Although such factors as temper-
ature, humidity, and precipitation might be presumed to influence indoor-outdoor
pollution relationships, no correlations could be established in the few studies in
which these conditions were reported. Wind speed and direction have been found
to affect the relationship in a number of instances, however. Closely associated
with these factors is the amount of natural ventilation of the building; i. e. , its
tightness and window and door openings. Very few data are available from which
to evaluate the effects of natural ventilation, but, in general, increased natural
ventilation appears to facilitate the penetration of pollutants into buildings.
Time - Indoor concentrations, outdoor concentrations, and indoor/outdoor ratios
have been found to vary on daily and seasonal bases. Much of the variation in in-
door/outdoor ratio can probably be explained by changes in outdoor concentrations
or in other factors discussed in this section. For instance, indoor/outdoor ratios
for particulate concentrations have been found to be lower in winter than in summer,
possibly because outdoor concentrations are higher during the winter or because
natural ventilation decreases when buildings are shut up for the winter.
48
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
One time-dependent factor, the so-called "lag time," affects indoor-outdoor
relationships independently, although lag time itself is affected by such factors
as natural ventilation. For many pollutants, indoor concentrations react more
slowly to changes in overall ambient air pollution than do outdoor concentrations.
This difference in reaction time can result in lower inside concentrations since
sharp outdoor peaks may be smoothed by the lag-time effect. It can also result
in indoor concentrations higher than outdoor concentrations when outdoor concen-
trations are falling. This effect is suspected as the cause in many of the instances
when indoor/outdoor percentages greater than 100 percent were reported. Lag
times have been identified for CO, SO2, and particulates, but no method is avail-
able for predicting their occurrence or effect.
Location - Indoor concentrations and indoor/outdoor ratios have been, found
to vary nationally, regionally, and locally. For the most part, however, these
variations are related to variations in outdoor concentration and can be predicted
if local outdoor concentrations are known. It should be kept in mind, however,
that outdoor concentrations and the resulting indoor concentrations can vary widely
within a small area depending on such factors as wind direction relative to major
pollution sources and the presence of locally significant sources such as garages
and filling stations.
Even within the same building, pollution levels may not be the same in dif-
ferent locations. Variations have been identified from room to room, from story
to story, and even from floor to ceiling and from exterior to interior walls within
the same room.
Type of Building - It seems logical to assume that indoor-outdoor pollution relation-
ships would be different for different types of buildings. Examination of the limited
amount of comparable data for the range of common outdoor concentrations does
not reveal a great deal of difference, however.
Air Conditioning and Filtration - Air-conditioning engineers are confident that
air-conditioning systems can be designed, built, and operated to remove air
pollutants. The degree of improvement in air quality obtained with air condition-
ing is dependent, however, on the type of air-cleaning equipment incorporated in
the system. Given the types of air-conditioning systems normally supplied up
until around 1970, air conditioning has very little effect on interior air quality.
Conclusion and Recommendations 49
-------
Pollen is indeed practically eliminated by air conditioning, even without the standard
roughing filters normally employed, and coarser particles may be reduced by the
standard filters; but other pollutants and smaller sized particles are generally
unaffected. Components are available that can reduce certain types of pollution,
and their use has received more attention in recent years.
Summary
Indoor air pollution is controlled primarily by outdoor pollution. The rela-
tionship is far from simple, however. It is affected by a large number of factors,
all of which must be considered if accurate estimates and meaningful measurements
of indoor concentrations are to be made. The data currently available are sufficient
only to suggest general patterns in the relationship between indoor and outdoor
pollution, and the effects of factors other than outdoor concentration are even less
well defined.
RECOMMENDATIONS
The conclusions presented above are admittedly tentative. They are thought,
however, to constitute the best basis currently available for estimating indoor
pollution, and they are recommended for this purpose until better information is
available.
Additional experimental work is badly needed to test the validity of these
conclusions, and it is suggested that the conclusions be considered in planning and
evaluating future studies. Some of the needed data are already being obtained or
analyzed. The Research Corporation of New England (formerly The Travelers
Research Corporation) and Arthur D. Little, Inc., are conducting research in
continuation of the studies reported in References 1 to 6 and in References 7 and 8,
respectively. The General Electric Company77 has also conducted research that
should help to better define indoor-outdoor pollution relationships, and the result of
these studies should also be considered in planning future studies if they are
available.
Review of the various studies and of the publications in which they are
described has lead to some suggestions which may be of value in planning, con-
ducting, and reporting future indoor-outdoor air pollution studies. First, because
of the strong dependence of indoor concentrations on outdoor concentrations, out-
door concentrations should be measured in any study in which indoor pollution is
50 INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
to be evaluated. If possible, both indoor and outdoor sampling should be conducted
over a period of at least several hours and the samples should be taken as simul-
taneously as possible because of lag-time effects.
In planning future studies, pollution sources both indoors and outdoors should
be considered. Several sampling points may be necessary inside and out to
determine the actual outdoor concentrations to which indoor levels are responding,
the influence of interior pollution sources, and the degree and rate of pollutant
penetration. Activities inside the building being sampled should be controlled,
limited, or at least recorded and considered in evaluating the results.
For particulate measurements, particle size distributions both indoors and
out should be determined, if possible, since particles of different sizes have dif-
ferent effects and may penetrate buildings at different rates. When bacteria and
fungi are measured, the types should be identified, if possible, and spore sizes
should be considered in analyzing the results to determine if differences in com-
position between indoor and outdoor population are the result of interior generation
or of selective penetration. Some method of normalizing results of fungus and
bacteria sampling is badly needed to facilitate comparison of results.
Since indoor-outdoor pollution relationships are highly complex and all of the
factors affecting the relationship may not yet be identified, it is very important
that test conditions and procedures be described in detail. At least those factors
discussed earlier in this chapter under "Other Factors Affecting Indoor Concentra-
tions, " as •well as sampling locations, procedures, and instrumentation, should be
described. Emphasis on test conditions and procedures should not be such, however,
that presentation and analysis of the results becomes secondary.
Analysis of results should begin with consideration of indoor-outdoor relation-
ships since outdoor concentrations have been identified as exerting a controlling
influence. Any other relationships developed in further analysis of the results
should also be examined for possible contributing factors such as those discussed
earlier.
Many of the publications reviewed in this survey were journal articles. Since
journal articles are necessarily general and limited in scope, some method needs
to be found to make the detailed data on which such articles are based readily
Conclusions and Recommendations 51
-------
available so that they can be considered for applications beyond the scope of the
published article. As an example, the American Institute of Chemical Engineers
places such data on file with the American Documentation Institute.
52 INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
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58
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
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APPENDIX A.
COMPILATION OF INDOOR-OUTDOOR AIR POLLUTION DATA
59
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Table A-l. INDOOR AND OUTDOOR CONCENTRATIONS OF SULFUR DIOXIDE
Location
Hartford, Conn.3
Hartfort,
Conn. a, 4
Cincinnati ,
Ohiol6
Moscow,
U.S.S.R.19
U.S.S.R.20
Rotterdam^!
Building
type
House
(Blinn St.)
House
(Carroll Rd. )
Houses
Hospital
Houses
Houses
House
Concentration, pphm
Indoor
1.4
0.3
0.8
3.7
2.8
3.2
78
5
6
10
12
14
16
18
30
30
40
10
38
1.52
Outdoor
0.4
0.1
0.2
0.0
0.3
0.2
10
14
8
16
24
32
40
48
100
60
70
15
42
7.47
Indoor/
outdoor, %
350
300
400
oo
935
1600
780
36
75
62
50
44
40
37
30
50
57
67
90
20
Remarks
Day
Night
Average
Day
Night
Average
Old coal -heated houseb
New coal -heated house
200 to 300 meters from industrial plant
800 to 1000 meters from industrial plant
Area away from industrial plant
Botanical garden (control area)
Near viscose plant
a
o
o
30
o
er
o
o
o
•30
-o
O
er
o
•30
m
o
C<0
Maximum concentrations are listed. Concentrations for other studies are
inside concentrations are presumed to be caused by a faulty heating
mean values.
system. Excluded from Figure 2-1.
-------
Table A-2. INDOOR AND OUTDOOR CONCENTRATIONS OF CARBON MONOXIDE
Location
Hartford,
Conn. ^
Moscow,
U.S.S.R.22
Buildinq
type
Library
City Hall
Office
(100 CP)
Office
(250 CP)
House
(Blinn St.)
House
(Carroll Rd.)
Houses
Season
Summer 1
Fall
Winter
Average
Summer
Fall
Winter
Average
Summer
Fall
Winter
Average
Summer
Fall
Winter
Average
Summer
Fall
Winter
Average
Summer
Fall
Wi nter
Average
Time
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Distance
from
source,
m
50a
100a-b
250a
500a
300C
800 to 1000C
Concentration,
ppm
Indoor
3.24
2.17
4.76
4.52
5.28
3.06
3.84
3.04
2.00
4.35
3.83
6.02
3.45
3.78
3.34
2.81
3.58
2.48
3.82
3.25
3.21
3.42
3.18
3.83
3.05
3.23
2.34
3.18
2.57
3.36
3.17
3.48
2.21
2.27
2.84
2.15
2.75
3.20
2.94
2.07
2.23
2.56
11.6
16.3
9.0
7.6
39.9
22.4
Outdoor
3.73
2.17
6.14
4.72
6.32
3.02
4.35
3.40
1.97
4.90
3.78
7.50
3.71
4.21
2.55
2.80
2.72
1.99
3.39
2.69
2.69
3.26
3.11
4.01
2.92
4.26
2.43
3.33
2.52
3.14
3.06
3.21
2.05
2.09
2.68
2.06
2.70
2.33
2.70
1.84
1.99
2.44
17.8
16.5
14.9
12.8
48.8
34.1
Indoor
outdoor,
%
87
100
78
96
84
101
88
89
102
89
101
80
93
90
131
100
132
125
113
121
119
105
102
96
104
76
96
96
102
107
103
108
107
108
106
104
102
96
108
112
112
105
65
99
60
59
82
66
aSource was plant with open hearth furnace.
t>Natural-gas equipped. Other homes in Russian study were not.
Figure 2-1.
cSource was plant with blast furnace.
Excluded from
Appendix A. Compilation of Data
61
-------
Table A-3. INDOOR AND OUTDOOR CONCENTRATIONS OF GASEOUS POLLUTANTS OTHER THAN S02 AND CO
Gas
Carbon
dioxide9
Nitrogen
dioxide
Carbon
bisulfide
Hydrogen
sulfide
Total
gaseous
acid
Location
Osaka,
Japan10
Los Angeles,
California"
U.S.S.R.20
U.S.S.R.20
Cincinnati ,
Ohio17
Cincinnati ,
Ohio18
Building
type
Offices
House
Houses
Houses
Old
peoples'
home
Houses
Concentration, pphma
Range
Indoor
0.06 to 0.32
0.08 to 0.28
0.04 to 0.09
0.06 to 0.23
0.04 to 0.13
0.03 to 0.14
0 to 9.5
1 to 11.5
_
-
3.3 to 13
0 to 3 . 5
-
Outdoor
_
-
-
-
-
0.03 to 0.04
1 to 12.5
1 to 12.5
1 to 12.5
1 to 12.5
_
-
1.8 to 14
1.8 to 14
-
Mean
Indoor
_
-
-
_
-
-
3.1
3.1
5.5
6.3
4
6
7.7
2.0
2.4
Outdoor
—
-
_
_
-
.
_
_
_
_
5
9
5.9
5.9
4.7
Indoor
outdoor,
%
_
-
-
_
-
-
_
_
_
_
80
67
131
34
51
Remarks
Office building
Old office building, winter
Old office building, summer
New air-conditioned
building, winter
New air-conditioned
building, summer
Newer air-conditioned
building
Room with activated carbon
filter
Room with no filter
Room with parti cul ate
filter
Room with no filter
Near viscose plant
Near viscose plant
Windows open
Windows closed
o
o
o
o
o
o
zo
-o
o
o
C/5
Carbon dioxide concentration in percent.
-------
Table A-4. INDOOR AND OUTDOOR CONCENTRATIONS OF PARTICULATES
Location
Hartford,
Conn.2
New York.
N. Y.30
West Queens,
N.Y.31
Oushambee,
U.S.S.R.29
Rotterdam,
Nether-
London,
England25-26
New York.
H-Y.32,33,b
Cincinnati ,
japan12-13
Building
type
Library
City Hall
Office
(100 CP)
Office
(250 CP)
House
(Blinn St)
House
(Carroll Rd)
Offices
Laboratories
Living rooms
Bedrooms
Overall
Houses
Houses3
First story
Second story
Houses
Laboratory
Offices
Laboratories
Living rooms
Bedrooms
Overall
Laboratory
Apartment
Season
or
month
Summer
Fall
Winter
Average
Summer
Fall
Winter
Average
Summer
Fall
Uinter
Average
Summer
Fall
Winter
Average
Summer
Fall
Winter
Average
Summer
Fall
Winter
Average
November
March
May
i mjr
June
Time
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Measurement
Weight,
wg/m3
Particle
count,
particles/
cm3
Concentration
Range Mean
Indoor
95 to 211
157 to 232
60 to 539
61 to 250
60 to 539
90 to 462
77 to 625
141 to 1880
152 to 740
50 to 860
148 to 1230
50 to 1880
570 to 4200
294 to 3714
230 to 2886
278 to 1494
Outdoor
41 to 938
101 to 480
75 to 800
74 to 1800
509 to 5009
372 to 4028
245 to 2874
295 to 1303
Indoor
60
43
57
44
67
45
54
78
49
82
50
87
51
66
50
46
36
27
38
39
39
56
60
38
23
60
32
45
70
56
54
45
49
35
52
76
47
76
38
53
33
54
158
239
1270
660
153
195
378
460
1287
978
738
Outdoor
132
82
150
100
425
189
180
153
78
133
94
327
168
159
104
93
48
38
124
81
81
124
109
66
46
183
97
104
79
65
96
74
114
86
86
66
56
78
61
103
85
75
212
226
960
960
184
205
512
120
1897
1528
1047
752
Indoor/
outdoor,
50
52
38
44
16
26
30
51
63
62
53
27
30
42
48
49
75
71
31
48
48
45
55
58
50
33
33
43
87
86
56
61
43
41
60
115
84
97
62
51
39
72
75
106
132
60
83
95
74
380
84
91
98
Appendix A. Compilation of Data
63
-------
Table A-4 (continued). INDOOR AND OUTDOOR CONCENTRATIONS OF PARTICULATES
Location
Osaka,
Japan11
Toyonaka .
Japan14
Novara ,
Italy37
Hartford,
Conn.2
Cincinnati ,
Ohio'8
Building
type
Apartment
Residential
store
Hospital
School
Apartment
Bedroom
Living room
Schools
Urban
Suburban-
residential
Suburban-
industrial
Rural
Library
City Hall
Office
(100 CP)
Office
(250 CP)
House
(Blinn St)
House
(Carroll Rd)
Houses
Season
or
month
November
March
May
June
Average
November
March
May
June
Average
Summer
Fall
Winter
Average
Summer
Fall
Winter
Average
Summer
Fall
Winter
Average
Summer
Fall
Winter
Average
Summer
Fall
Winter
Average
Summer
Fall
'(inter
Average
Time
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
"ight
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Day
Night
Measurement
Particle
count,
Particles/
cm3
Soil ing
index,
Cohs/1000
linear ft
Concentration
Range
Indoor
4 4 to 1747
83 to 2144
421 to 4195
513 to 7439
Outdoor
296 to 2058
117 to 1790
410 to 4166
627 to 7592
Mean
Indoor
706
662
1611
2382
1654
1839
1497
1115
1091
1001
726
807
1216
1839
1899
160Z
1081
931
1020
670
732
1222
368
258
340
444
0.34
0.25
0.33
0.32
0.29
0.24
0.30
0.40
0.30
0.38
0.33
0.49
0.41
0.38
0.26
0.30
0.19
0.19
0.35
0.34
0.27
0.26
0.32
0.22
0.21
0.42
0.35
0.30
0.39
0.45
0.30
0.31
0.33
0.37
0.36
0.38
0.42
0.26
0.24
0.27
0.30
0.31
2.1
Outdoor
619
678
1595
2346
2133
1839
1801
1319
1129
1060
703
786
1346
2133
1839
1801
1319
1129
1060
703
786
1346
662
280
752
690
0.42
0.31
0.36
0.34
0.58
0.49
0.42
0.41
0.30
0.33
0.29
0.52
0.44
0.38
0.30
0.36
0.27
0.24
0.41
0.38
0.33
0.46
0.52
0.28
0.25
0.72
0.64
0.48
0.44
0.53
0.33
0.35
0.40
0.50
0.42
0.32
0.38
0.34
0.36
0.29
0.36
0.34
3.8
Indoor/
outdoor.
114
98
101
102
78
100
83
85
97
95
103
103
90
86
103
89
82
82
96
95
93
91
56
92
45
64
81
81
92
94
50
49
72
98
100
115
114
94
93
100
87
83
69
79
85
89
82
57
62
79
84
58
55
63
89
85
88
89
82
74
86
119
110
80
67
93
83
91
55
Hear main traffic.
Concentrations reported in particles per cubic foot; conversion accurate to three significant digits.
64
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
Table A-5. INDOOR AND OUTDOOR CONCENTRATIONS OF FUNGUS SPORES
o
o
o
=3
Location
Philadelphia,
Pennsylvania^
St. Paul,
Minnesota44
Galveston,
Texas45
London,
England45
Oereboro.
Sweden49
Copenhagen,
DenmarkSO
Madrid, SpainSl
Spanish coastal
Lexington.
Kentucky52
Tucson,
Arizona5^
Cardiff.
Wales54
Stockholm,
Sweden55
Copenhagen,
Denmark5^
Cardiff.
Wales57
Stockholm,
Sweden5**
Building
type
Houses
Houses
Office
Houses
Houses
Houses
-
-
Theater
and two
houses
Houses
House
House and
Office
Apartmenl
Hospital
Hospital
Public
building
Public
building
Duration
of
exposure,
minutes
15
12
2
-
30
15
-
15
15
10
15
-
-
Measure-
ment
Colonies/
sample
Colonies/
Total
colonies
Grains/nr
Total
colonies
Concentration
Range
Indoor
0 to 25
0 to 20
0 to 23
0 to 28
4 to 46
0 to 13
5 to 34
33 to 115
Outdoor
0 to 35
0 to 35
13 to 80
7 to 32
38 to 125
Mean
Indoor
8
11
22
5
12
16.3
60
5
55
30.4
1 ,808
1 ,187
1,199
224
203
208
422
1,289
6,135
5.7
205
506.
89.7
540
Outdoor
38
12.9
76
13
13
35.3
478
515
3,978
306
1 ,209
1,209
1,209
6,859
12,712
10.0
2,609
6,520
6,896
1,572
Indoor/
outdoor,
723
523
32
126
79
38
423
86
378
230
30
73
17
18
35
19
48
57
7.9
7.8
1.3
34
Remarks
Room with air conditioner
Room without air conditioner
Early morning
Before sweeping
After sweeping
Late evening
Overall
Col oni es/sampl e-day
Dry, clean conditions
Poor hygenic conditions
Summer
Winter
Air conditioned
Air conditioned with filter
Evaporative cooler
Based on maximum concentrations.
-------
Table A-6. INDOOR AND OUTDOOR CONCENTRATIONS
OF SPECIFIC FUNGUS SPORES
Fungus
Penicillium
Cladosporium
Aspergillus
Hormodendron
Mycelia sterilia
Mucor
Reference
52
46
58
50
51
54
55
56
57
58
51
54
55
56
52
58
51
54
55
56
50
56
51
54
55
52
58
51
Mean
concentration9
Indoor
752
125
28
200
18.0
1325
726
194
3005
3.4
205
224
5.3
122
324
258
463
1573
0.9
210
64
23
7
21
53
187
0.2
3.7
0.8
2
5
349
184
149
35
9
11
15
Outdoor
2379
211
37
116
5.2
58
112
668
1692
0.6
2609
2675
2025
585
330
290
3097
5984
4.4
883
71
37
4
7
204
136
0
18.8
4.4
3
3
1171
761
0
0
10
3
2
Indoor/outdoor,
%
32
59
76
172
346
2284
648
29
178
567
7.9
8.4
0.3
21
98
89
15
26
20
24
90
62
175
300
26
138
QO
20
18
67
167
30
24
00
00
90
367
750
66
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
Table A-6 (continued). INDOOR AND OUTDOOR CONCENTRATIONS
OF SPECIFIC FUNGUS SPORES
Fungus
Mucor (continued)
Pul lulan'a
Yeasts
Alternaria
Phoma
Oospora
Botrytis
Epicoccum
Sterile hyphae
Monilia
Reference
55
56
58
50
54
55
51
55
52
58
50
51
54
55
58
50
54
55
52
51
54
54
55
56
54
55
52
52
54
55
Mean
concentration^
Indoor
77
0.3
34
3.1
25
256
132
157
513
0
0
5
0.4
4
2
0
46
6
0.1
6
22
80
0
0
0
71
29
53
0.1
9
15
7
0
0
0
9
21
Outdoor
69
0.1
164
6.2
588
720
60
91
1924
298
7
44
0.9
10
6
44
234
8
0.5
199
108
32
0
1
1
144
160
328
0.5
152
178
91
0
1
0
21
0
Indoor/outdoor,
%
112
300
21
50
4
36
220
173
27
0
0
11
44
40
33
0
20
75
20
3
20
250
0
0
49
18
16
20
6
8
8
0
43
00
Appendix A. Compilation of Data
67
-------
Table A-6 (continued). INDOOR AND OUTDOOR CONCENTRATIONS
OF SPECIFIC FUNGUS SPORES
Fungus
Stemphylium
Tor ul ops is
Torula
Rhodotorula
Sporotrichum
Candida
Fusarium
Aleurisma
Basidiomycetes
Rhizopus
Ascomycetes
Reference
52
55
58
54
58
54
54
55
55
57
55
55
57
Mean
concentration9
Indoor
0
0
24
37
9
20
24
14
30
31
70
2.8
18
13
62.5
Outdoor
289
17
66
292
25
107
105
113
238
48
1276
1618
48
12
1294
Indoor/outdoor,
%
0
0
36
13
36
19
23
12
13
65
5.5b
0.2C
38
108
4.8b
aSee Note below for units of measure and study location.
b,
Hospital.
cPublic building.
NOTE:
Reference
Measurement
Location/condition
52
57
58
50
51
54
55
56
46
Total colonies; 15-min
exposure
Grains/m3; 24-hr con-
centration
Total colonies
Colonies/sample; 15-
min exposure
Colonies/m3
Total colonies, 10-min
exposure
Total colonies
Total colonies; 15-min
exposure
Colonies/sample
Theater and two houses, Lexington,
Kentucky. First measurement is
summer; second winter
Cardiff, England. First two
measurements for hospitals; third
for public building
Laboratory, Stockholm, Sweden
Homes, Copenhagen, Denmark
First measurement for Madrid, Spain;
second for Spanish coast
Houses, Cardiff, Wales
House and office, Stockholm,
Sweden
Apartment, Copenhagen, Denmark
Houses, London, England
68
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
Table A-7. FUNGUS SPORE COMPOSITION OF INDOOR AND OUTDOOR SAMPLES IN EUROPEAN STUDIES
Fungus
Penicillium
Cladosporium
Aspergillus
Hormodendron
Mycelia sterilia
Mucor
Pullulariji
Yeasts
Alternaria
Phoma
Oospora
Botrytis
Epicoccum
Monilia
Stemphyl ium
Torulopsis
Torifla
Rhodotorula
Sporotrichum
Candida
Fusarium
Al euri sma
Basidiomycetes
Rhizopus
Percent of total colonies
Stockholm
Sweden53
Indoor
37.0
22.6
4.3
-
-
1.7
6.3
-
0.9
1.1
-
-
-
-
-
6.8
-
3.7
-
-
-
-
-
-
Outdoor
7.4
37.2
2.4
-
-
0.6
10.4
-
2.8
0.5
-
-
-
-
-
18.6
-
6.8
-
-
-
-
-
-
Stockholm
Sweden55
Indoor
49.0
25.6
3.0
-
3.0
1.3
4.2
8.4
0.7
0.4
-
0.9
0.2
0.3
0.4
-
-
-
-
-
0.5
0.5
0.3
0.2
Outdoor
13.3
47.1
1.1
-
6.0
0.5
5.7
15.1
1.8
0.8
-
2.6
1.4
0
0.5
-
-
-
-
-
1.9
0.4
0.4
0.1
Oereboro,
Sweden49
Indoor
44
_
6.2
28
-
2.8
5.6
10
2.1
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Outdoor
11
_
1.3
68
-
-
6.6
3.6
-
-
-
1.5
-
-
-
-
-
-
-
-
-
-
-
-
Copenhagen,
Denmark50
Indoor
59
_
14
12
-
0.7
10
-
1.3
0.3
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Outdoor
15
_
-
53
-
_
18
-
2.6
1.5
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Copenhagen,
Denmark56
Indoor
59.6
15.8
3.5
14.0
-
5.3
-
-
-
-
-
1.8
-
-
-
-
-
-
-
-
-
-
-
-
Outdoor
6.0
44.0
0
44.0
-
1.0
-
-
-
-
-
5.0
-
-
-
-
-
-
-
-
-
-
-
-
Cardiff.
Wales54
Indoor
15.1
35.9
4.1
-
27.1
_
1.9
-
0
0.5
5.5
2.2
0.7
0.7
-
-
0.7
-
1.9
1.1
-
-
-
-
Outdoor
9.7
45.2
3.0
-
17.1
_
8.6
-
0.6
2.9
2.1
2.3
2.2
0.3
-
-
0.4
-
1.5
1 .6
-
-
-
-
Spain5!
Madrid
Indoor
73.3
17.9
0.4
-
0.1
0.6
-
7.3
0.2
-
0
-
-
-
-
-
-
-
-
-
-
-
-
-
Outdoor
12.2
69.0
0.9
-
0.6
0.7
-
12.5
2.1
-
0.2
-
-
-
-
-
-
-
-
-
-
-
-
-
Coast
Indoor
61.2
21.7
1.8
-
0.4
1.3
-
13.2
0.2
-
0
-
-
-
-
-
-
-
-
-
-
-
-
-
Outooor
21.8
56.4
1 .4
-
0.6
0.4
-
17.6
1.1
-
<0.1
-
-
-
-
-
-
-
-
-
-
-
-
-
o
o
o^
o
ET
-------
Table A-8. FUNGUS SPORE COMPOSITION OF INDOOR AND OUTDOOR
SAMPLES OF UNITED STATES STUDIES
Fungus
PeniciTMum
Aspergillus
Hormodendron
Mycelia sterilia
Mucor
Pullularia
Alternaria
Oospora
Botryodiplodia
Sterile hyphae
Stemphylium
Candida
Fusarium
Rhizopus
Helminthospon'um
Curvularia
Bisporia
Percent of total colonies
Lexington, Kentucky^2
Summer
Indoor
67.2
17.5
12.4
0
6.7
0.6
0
Outdoor
59.8
22.2
0
7.5
0.8
2.3
7.3
Winter
Indoor
55.8
28.6
15.6
0
0
0
0
Outdoor
69.0
23.2
0
2.3
0
0
5.5
Tucson, Arizona53
Indoor and outdoor
7.1
9.4
13.6
3.1
14.7
34
0.23
0.3
0.6
1.9
0.9
8.2
2.0
1.4
70
INDOOR-OUTDOOR POLLUTION RELATIONSHIPS
-------
Table A-9. RANGE AND OCCURRENCE OF FUNGUS SPORES IN INDOOR
AND OUTDOOR SAMPLES, UNITED STATES AND EUROPEAN STUDIES3
Fungus
Penicillium
Cladosporium
Aspergillus
Hormodendron
Mycelia sterilia
Mucor
Pullularia
Yeasts
Al ternaria
Phoma
Oospora
Botrytis
Epicoccum
Sterile hyphae
Monilia
Stemphylium
Torulopsis
Torula
Rhodotorula
Sporotrichum
Candida
Fusarium
Aleurisma
Basidiomycetes
Rhizopus
Range,
percent of total colonies
Indoor
15.1 to 73.3
15.8 to 35.9
0.4 to 28.6
12 to 28
0.1 to 27.1
0.6 to 15.6
1.9 to 10
7.3 to 13.2
0 to 2.1
0.3 to 1.1
0 to 6.7
0.9 to 2.2
0.2 to 0.7
0 to 0.6
0.3 to 0.7
0 to 0.4
6.8
0.7
3.7
1.9
1.1
0.5
0.5
0.3
0.2
Outdoor
6.0 to 69.0
37.2 to 69.0
0 to 23.2
44.0 to 68
0.6 to 17.1
0 to 1.0
5.7 to 18
3.6 to 17.6
0.6 to 7.5
0.5 to 2.9
0 to 2.1
1.5 to 5.0
1.4 to 2.2
0 to 2.3
0 to 0.3
0.5 to 7.3
18.6
0.4
6.8
1.5
1.6
1.9
0.4
0.4
0.1
Occurrence
Indoor
10
6
10
3
4
9
5
4
6
4
2
3
2
2
2
1
1
1
1
1
1
1
1
1
1
Outdoor
10
6
8
3
4
5
5
4
8
4
4
4
2
2
2
3
1
1
1
1
1
1
1
1
1
aDoes not include Tucson, Arizona, study shown in Table A-7b, since
indoor and outdoor percentages were combined.
Appendix A. Compilation of Data
71
-------
Table A-10. INDOOR AND OUTDOOR POLLEN CONCENTRATIONS
Location
Philadelphia,
Pennsylvania^
Philadelphia,
Pennsylvan1a59
Philadelphia,
Pennsylvania^
Chicago,
Illinois61
Baltimore,
Maryland^
Cardiff,
Wales57
Ann Arbor,
Hichigan°2
Pittsburgh,
Pennsylvania6^
Richmond,
Virginia^
Chicago,
Illinois65
Building
type
Houses
Houses
Hospital
Hospital
School
House
Hospital
Hospital
Public building
Test building
Hospital
Hospital
Hospital
Measurement
Grains/m^
Number/
sample
Grains/day
Grains/cm2
Concentration
Range
Indoor
0 to 74
0 to 28
12.7 to 98.2
12.4 to 141
0.4 to 2.8
0.4 to 2.8
11.9 to 68.3
26.8 to 82.0
0.7 to 2.6
0.7 to 6.6
6.6 to 392
1.3 to 23.6
1 to 86
1 to 37
7 to 407
0 to 2
0 to 23
Outdoor
0 to 1100
0 to 1100
2 to 1100
2 to 1100
2 to 1100
2 to 1100
31.9 to 110
31.9 to 110
31.9 to 110
31.9 to 110
60.0 to 272
60.0 to 272
60.0 to 272
60.0 to 272
14.4 to 914
14.4 to 914
2 to 162
5 to 251
71 to 1188
71 to 1188
10 to 350
Mean
Indoor
11
11
2
2
42.2
53.5
1.6
1.0
33.8
57.9
1.6
2.6
92.8
7.9
18
8
6.7
1.8
1.7
6.6
9.5
9.1
14.1
17.7
40.3
13.5
144
0
6
Outdoor
205
205
205
205
61.8
61.8
61.8
61.8
119
119
119
119
262
262
42
67
496
90.9
134.7
37.4
13.4
21.9
20.8
52.8
92.2
34.3
1539
1539
133
Indoor/
outdoor,
6
2
5
5
1
1
68
86
2
2
28
49
1
2
36
3
43
12
1.4
2.0
1.3
18
71
42
68
34
44
39
9.4
0
23
0.2
4.5
Remarks
Without air conditioner
With air conditioner
Non-air-conditioned house 1
Air conditioner and air filter off Test
Air filter off I house
Air conditioner and air filter on
Windows open 1 N filter
Windows open uith air purifier in air
Air conditioned \ conditioner
Air conditioned with air purifier conditioner
Windows open Standard
Windows open uith air purifier / f^?"° ?
Air conditioned . l^r
Air conditioned with air purifier } conditioner
Without air filter
With air filter
Day
Night
Window closed, <8 mph wind
Window closed, >8 mph wind
Window open 1 inch, <8 mph wind
Window open 1 inch, >8 mph wind
Window open 3 inches, 3 to 5 mph wind
Window open 12 inches, 4 to 5 mph wind
Average
Without air filter
With air filter
Non-air-conditioned room
Air-conditioneJ room
With air filter
o
o
o
o
o
20
-o
o
m
>
H
o
oo
Unpublished data furnished by Mr. M. B. Rhyne.
-------
a>
3
a.
O
o
=i
o
a
a>
ST
Table A-ll. INDOOR AND OUTDOOR CONCENTRATIONS OF BACTERIA
Type
Total bacteria
Streptococci
Microbes
(bacteria
and spores)
Location
Osaka, Japan^
Toyonaka,
Japan14
Philadelphia,
Pennsylvania^
New York,
New York66
New York,
Mew York66
Building
type
Apartment
House
Apartment
Houses
Offices
Schools
Offices
Schools
Measurement
Colonies/
sample,
5-min.
exposure
Bacteria/
sample,
5-min.
exposure
Colonies/
sample,
1 5-min.
exposure
Number/
100 ft3
Number/
ft3
Concentration
Range
Indoor
5 to 126
8 to 134
2 to 68
4 to 78
0 to 45
0 to 45
Outdoor
7 to 147
7 to 147
1 to 118
1 to 118
0 to 60
0 to 60
Type
Indoor
27
40
16
18
57
71
35.0
44.0
13.0
18.0
22
30
87
96
Outdoor
16
43
21
8
4
6
43.0
43.0
21.0
21.0
11
11
52
72
Indoor
outdoor,
%
169
93
76
225
1,425
1,183
82
102
62
86
75a
75a
200
273
167
133
Remarks
October-November (48-hr
cul ture)
May
June
October-November (24-hr
culture)
October-November (24-hr
culture)
October-November (48-hr
culture)
Living room .,
Bedroom May
Living room .
Bedroom June
With air conditioner
Without air conditioner
Averaoe for cultures at
20° and 37° C
Cultures at 20° C
Based on maximum values.
------- |