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OCR for page 11
I-)
Environmental Criteria
Long-term preservation of the paper-based collections at the National
Archives requires that damage caused by environmental conditions and atmo-
spheric pollutants be prevented. Because these documents, or at least their infor-
n~ation content, must be retained indefinitely, even very slow rates of deteri-
oration caused by air pollutants could lead to unacceptable levels of accumulated
damage over a period of several hundred years. The problem of protecting the
National Archives inventory is thus quite different from the question of protecting
common consumer products from premature deterioration over their short serv-
ice lifetime. Standards adopted for acceptable air quality outdoors therefore are not
applicable, and separate air quality objectives must be set that are suited to the
problem of long-term preservation of archived materials.
MATERIALS CONSIDERED
At the outset, it Is necessary to recognize that document collections contain
much more than just paper. Paper-based records sometimes are written in colored
inks. Maps may be printed with colored inks or tinted with pigments. Some
records are bound into volumes, and those bindings may contain thread, card-
board, adhesives, cloth, leather, and synthetic or chemically impregnated fabrics.
Air pollution can cause damage to all these materials. In addition, paper-based
records are sometimes converted to other media {e.g., photographic film or mag-
netic tapes, and those materials also must then be protected.
AIR POLLUTANTS
Pollutants present in outdoor air may be drawn into buildings by conven-
tional ventilation systems. Under authority derived from the Clean Air Act t42
USC 1857 et seq. I, the U.S. Environmental Protection Agency {EPA) has adopted
National Ambient Air Quality Standards for six common outdoor pollutants:
11
OCR for page 12
12
PRESERVATION OF HISTORICAL RECORDS
TABLE 3-1 National Ambient Air Quality Standards
National Standard
Pollutant Averaging Timea Primaryb SecondaryC
Ozone 1 hour 235 ,ug/m3 Same as primary standard
(0.12 ppm)
Carbon monoxide 8 hour 10 mg/m3 Same as primary standard
(9 ppm)
1 hour 40 mg/m3
(35 ppm)
Nitrogen dioxide Annual average 100 ,ug/m3 Same as primary standard
(0.05 ppm)
Sulfur dioxide Annual average 80 ,ug/m3
(0.03 ppm)
24 hour 365 ,ug/m3
(0 14 ppm)
3 hour
Suspended
particulate mean
matter
Annual geometric 75 ,ug/m3
1300 ,ug/m3
(0 5 ppm)
60 ,ug/m3
24 hour 260 ,ug/m3 150 ,ug/m3
_ Calendar quarter 1.5 ,ug/m3 Same as primary standard
.
aAveraging times shown are the durations over which measurements are averaged for comparison to
the standards.
bPrimary standards are set to protect human health.
CSecondary standards that differ from primary standards are set in response to welfare effects includ-
ing damage to materials.
SOURCE: Environmental Protection Agency (1971, 1978b, 1979).
sulfur dioxide tSO2), nitrogen dioxide tNO2), ozone tO3J, carbon monoxide {CO),
suspended particulate matter, and lead, as shown in Table 3-1. The primary stan-
dards shown are at levels deemed necessary to protect human health, while the
secondary standards for SO2 and particulate matter have been adopted to take
additional steps to slow the rate of damage to the public welfare E.g., plant life,
animal life, and materials) from those pollutants. Because of their regulated status
and because they have been readily measurable for many years, much literature
has been accumulated that can be used to characterize the atmospheric loading
and the damage potential of these pollutants Environmental Protection Agency,
1978a, 1982a, 1982b).
A variety of additional air pollutants are recognized for which outdoor air
quality standards have not been set at a national level. A selected list of unregu-
lated pollutants is shown in Table 3-2. These unregulated pollutants include acid
gases initric acid tHNO3), nitrous acid tHONO), formic acid {HCOOH), acetic
acid {CH3COOH), hydrochloric acid tHClJ], oxidants [peroxyacetyl nitrate
(CH3COO2NO2) and hydrogen peroxide tH2O2~], and reduced nitrogen and sulfur
compounds [NH3, H2S) that fall within categories known to cause damage to
materials such as those found in archives.
In the case of particulate air quality, difficulty arises if one tries to relate gross
measures, such as total suspended aerosol mass concentration, directly to materi
OCR for page 13
ENVIRONMENTAL CRITERIA
13
als damage effects. A variety of chemically and physically distinct subfractions of
the particulate matter complex can be identified that may have a higher potential
for material damage than the bulk of the aerosol mass, including acid particles
{e.g., H2SO4 mist), alkaline particles E.g., cement dust), and black soot particles.
Acid mists and soot particles are often concentrated in particle sizes less than 1 ,um
in diameter that are relatively difficult to remove when compared to coarser
particles several micrometers in diameter. Unless a more sophisticated definition
of particulate air quality is adopted than one based solely on total aerosol mass
concentration, there is a danger that ventilation systems will be designed that will
lower mass loadings without achieving a proportionate reduction in damage
potential.
In addition to pollutants commonly found outdoors, air quality in buildings
can be affected by contaminants emitted indoors. Indoor generation of pollutants
in museums, archives, and libraries recently has been reviewed by Baer and Banks
{1985a). They report a variety of sources, including formaldehyde and alkaline
TABLE 3-2 Partial List of Unregulated Gaseous Contaminants
Observed or Possibly Present in Polluted Outdoor Air
Compound
1. Compounds observed in photochemical smoga
Peroxyacetyl nitrate, CH3C0O2NO2
Hydrogen peroxide, H2O2
Formaldehyde, CH2O
Higher aldehydes, RCHO
Acrolein, CH2CHCHO
Formic acid, HCOOH
Typical (or Maximal)
Concentration Reported,
ppm
0.004 (0.01)
(0. 18)
0.04
0.04
0.007
(0.05J
2. Compounds that may be formed in
photochemical smoga b
Peroxybenzoyl nitrate, C6H5COO2NO2 (PBzNJ
Nitric acid, HONO2
Organic hydroperoxides, ROOH
Organic peracids, RCOO2H
Organic peroxynitrates, RO2NO2
Ozonides, O3-olefin
Ketene, CH2CO
Nitrous acid, HONO
Pernitric acid, HO2NO2
Pernitrous acid, HO2NO
Sulfoxyperoxy nitrate, HOSO2O2NO2
3. Other unregulated air pollutants
NH3, H2S, HC1
NOTE: A comprehensive 24-page list of more than 150 chemical substances that
are regulated as air pollutants in jurisdictions throughout the world is given by
Newill (1977J.
aCommittee on Medical and Biologic Effects of Environmental Pollutants (1977).
bSome of the compounds listed under number 2 are speculative; concentrations
have not been quantified.
OCR for page 14
PRESERVATION OF HISTORICAL RECORDS
:~4':
Historical records requiring immediate preservation to avoid loss of
information. Damage can result from deterioration of the paper, ink, and
binding as well as from handling.
OCR for page 15
ENVIRONMENTAL CRITERIA
15
particles Setting concreted released from building materials; corrosion inhibitors
{e.g., diethylaminoethanolJ introduced from improperly designed air humidifica-
tion systems; oxides of nitrogen generated by decomposition of cellulose nitrate
found in some photographic film, "acetate" recording disks, adhesives, and
pyroxylin-coated or -impregnated fabric Often used in library rebindingsJ; and
organic acids (e.g., formic, acetic, and tannic acid J that are released by off-gassing
from certain wood products and from decomposition of adhesives ;e.g., polyvinyl
acetate!.
OBSERVED DAMAGE
The following discussions cover previously observed damage to materials
similar to those found in archives.
Paper
Chapter 4 of this report indicates that acidification of paper leads to destruc-
tion of its mechanical properties via hydrolysis of the cellulose of the paper.
Absorption of acid gases by paper can accelerate this acidification process, with
resulting increased hydrolysis. Sulfur dioxide is readily absorbed by uncoated
wallpaper, but the absorption process can be retarded by vinyl coatings on the
paper surface ;Spedding andRowlands, 1970; Walsh et al., 1977J. Once absorbed by
the paper, SO2 can be oxidized, thereby contributing to the acidity of the paper.
Examination of book collections has shown that acidity is highest at the exposed
outer edges and declines toward the center of the pages, a phenomenon that has
been associated with SO2 absorption at the exposed edges of the books {Parker,
1955; Hudson, 1967J. Accelerated hydrolysis of paper by acid gases other than SO2
is less well documented. As will be discussed shortly, reduction in the strength of
cotton textile fibers has been observed from exposure to ambient air containing
NO2 in the presence of sunlight. It is reasonable, therefore, to expect that NO2 and
other acid gases may promote the failure of cellulose fibers in paper.
Paper-based materials are subject to deterioration by oxidation as well as by
hydrolysis. Ozone will react with cellulose. However, its effect at ambient con-
centrations on the storage properties of paper records is not well documented.
Although dose-response relationships for pollutant damage at low concentrations
have not been experimentally established, one can infer a linear relationship based
on measurements made at the ppm level tH. H. G. lellinek, presentation to the
committee, 1985J.
Soiling of paper can result from the deposition of atmospheric particulate
matter. Perceptual experiments show that white paper should appear soiled when
only 0.2 percent of its surface has been covered with black deposited particles
{Carey, 1959J. Experiments by Hancock et al. {1976J confirmed that with maxi-
mum contrast a 0.2 percent effective area coverage by black particles represents
the median threshold for detection of soiling by human observers. Hancock and
his coworkers also coated common household items "including bond papery with
charcoal aerosol deposits at a variety of surface coverage densities. The median
response of a panel of human subjects indicated that the test articles were "unfit
for use" once the effective area coverage by black particles reached 0.7 percent.
The relationship between atmospheric particulate matter loading and soiling of
OCR for page 16
16
PRESERVATION OF HISTORICAL RECORDS
surfaces le.g., paper) is not completely understood. "The poorly understood depo-
sition rates and poorly characterized chemical and physical properties related to
reflectance make general application of . . . "damage] functions difficult if not
impossible" {Environmental Protection Agency, 1982a). However, important
insights into the likely nature of the soiling of paper can be inferred from studies of
the optical and chemical properties of ambient particulate matter collected on
filters.
Recent atmospheric optical studies show that light absorption in urban
atmospheres is dominated by the presence of small amounts of black carbona-
ceous material having a structure similar to that of impure graphite, often referred
to as graphitic carbon, elemental carbon, or sometimes just soot. Examination of
the decrease in reflectance of paper on which atmospheric particles have been
collected by filtration shows that the reflectance decrease is due principally to the
elemental carbon content of the aerosol {sass et al., 1984J. Diesel engine soot is a
prominent source of elemental carbon in cities, although more than 50 other
sources can be identified that contribute carbon particles to the atmosphere {sass
et al., 1984~. These elemental carbon particles are found predominantly in fine
particle sizes, below 2,um in diameter, and represent only a very small fraction of
the ambient aerosol mass {about 5.5 ,ug/m3 annual mean at downtown Los
Angeles in 1975, versus a total aerosol mass of over 100,ug/m3 in that year at that
site) Mass et al., 1984~. The characteristic color of coarse particle samples {diame-
ter greater than 2,um) is brown because of the presence of soil or road dust. Thus,
the appearance of deposited particles would be expected to vary as a function of
size and chemical composition.
While the soiling of paper as a function of particle size and chemical composi-
tion has not been extensively studied, the chemical composition of soiling
deposits on Plexiglas display cases in a Los Angeles museum has been examined
;Druzik, personal communication, 1984~. These deposits appeared on the
unwiped inside surfaces of the display cases over only a 3-month period following
the opening of an exhibition. Chemical analysis showed that the deposits con-
tained carbonaceous material, with 21 percent to 30 percent of the carbon present
as black elemental carbon, which is the ratio of elemental carbon to total carbon
close to that observed in atmospheric aerosol samples in downtown Los Angeles
[sass et al., 1984~. This study, plus experience with particle samples filtered from
the atmosphere onto paper substrates, suggests that both coarse and fine particles
must be controlled if these colored atmospheric materials {i.e., elemental carbon
and soil dust types) are to be eliminated as a potential source of soiling.
Leather
Leather is a common material found in the bindings of old books and docu-
ments. Absorption of SO2 by leather is rapid, resulting in hydrolysis of the leather
material, followed by cracking and eventual powdering of the leather (Spedding et
al., 1971; Yokom and Grappone, 1976~.
Textiles
Cloth and thread are used in library and document collection bindings. Cellu-
losic fabrics, like cotton, rayon, and certain types of nylon, are particularly suscep
OCR for page 17
ENVIRONMENTAL CRITERIA
1
Bound volumesin storage stacks at the NationaJArchives. Leatherand
cloth, as wed as paper, pigments, andinks, are affected by
environmental conditions.
OCR for page 18
18
PRESERVATION OF HISTORICAL RECORDS
tible to air pollutant damage. Upon exposure to SO2' the breaking strength of
cottonisreduced{Bryssonetal.,1967;Zeronian, 1970;Zeronianetal.,1971~.The
strength of cotton also was reduced by exposure to sunlight and ambient air in
Berkeley, Califomia, under circumstances that implicate NOX species as the dam-
aging agents Morris, 1966~. Like paper, cellulosic fabrics can degrade by oxida-
tion. Studies of the effect of ozone exposure on cotton textiles {Bogarty et al., 1952;
Morris, 1966) showed a loss in tensile strength in the wetted samples studied, but
no apparent loss in dry fabric samples. Textiles used in bookbinding would be
expected to be vulnerable to soiling by atmospheric particulate matter {see pre-
vious discussion of soiling hazard to paper).
Dyes, Pigments, and Inks
In the late 1930s it was found that commercial textiles treated with a blue
anthraquinone dye reddened when exposed to nitrogen dioxide {Rowe and Cham-
berlain, 1937; Salvin et al., 1952~. NO2-resistant dyes were formulated and used in
comparative tests during the mid-1950s in several cities believed to represent
different levels of pollutant exposure. It was found that textiles exposed to the
atmosphere in Ames, Iowa, still faded rapidly but without noticeable reddening
and that this second type of fading was due to the reaction with atmospheric ozone
{Salvin and Walker, 1955; Salvin, 1969J. Recent studies j Shaver et al., 1983) show
that several widely used artists' pigments will fade rapidly upon exposure to ozone
at levels found in Los Angeles photochemical smog. Such ozone-fugitive pigments
identified to date include the alizarin lakes and natural yellow pigments used in
Japanese woodblock prints. Air pollution-induced fading of inks used in preparing
written and printed documents has not been studied to date, but given the chemi-
cal similarities between inks and other types of colorants {dyes and pigments) one
may assume that at least some inks are pollutant-sensitive.
Adhesives
Although only limited literature on pollution-induced failure of adhesive
joints exists, substantial evidence can be found of pollution damage to the poly-
mers used in formulating adhesives. From these data, one may expect oxidation in
these polymer systems and acid hydrolysis in special cases tH. H. G. lellinek,
presentation to the committee, 1985~.
Corrosion of Metals
In common experience, paper clips, staples, and other metal fasteners corrode
and stain paper-based documents stored in poorly controlled environments. How-
ever, such effects have seldom been observed in documents stored under good
environmental conditions at the National Archives, and virtually none for the
post-1940 records.
Photographic Film
As is discussed in Chapter 5, photographic film is sensitive to NO2 exposure
[Carroll and Calhoun, 1955~. Exposure to atmospheric oxidants {e.g., ozone or
OCR for page 19
ENVIRONMENTAL CRITERIA
19
peroxides) can cause the formation of microblemishes ;McCamy, 1964; Henn et
al., 1965; Weyde, 1972~. Since information often is recorded at high magnification
on microfilm, there is concern about the development of even small defects such
as microblemishes.
Unregulated Pollutants
In the foregoing summary, little mention was made of any damaging effects of
unregulated pollutants like those listed in Table 3-2. Most of the listed pollutants
simply have not been tested in combination with the materials of interest to see if
damage will result. This information vacuum should not be misinterpreted as
indicating that the unregulated pollutants have no effect.
INDOOR POLLUTANT LEVELS
Whether or not a particular air pollutant represents a threat to archived mate-
rials depends on whether or not it is found in the indoor atmosphere of buildings.
Transfer of the criteria pollutants E.g., SO2, NO2, 03, and particulate matter) from
outdoors to the indoor atmosphere of libraries, archives, and museums has been
studied in a few cases. Data available for buildings in a variety of cities can be
organized so that the percentage attenuation of outdoor pollutant levels on intro-
duction to the indoor environment by building ventilation systems is apparent.
Sulfur Dioxide Levels
In the absence of deliberate pollutant removal, the indoor level of the pollu-
tants generated outdoors might be expected to approach the level in the outdoor air
that feeds building ventilation systems. Thomson {1965) reported that sulfur
dioxide levels inside non-air-conditioned spaces at the National Gallery in London
and at the Victoria and Albert Museum range from 50 percent to 100 percent of the
outdoor concentration. Recent SO2 measurements by Hackney ~ 1984) in areas of
the Victoria and Albert Museum, which lacks an SO2 removal system, show SO2
levels of 9 ppb in a typical internal gallery when the level outside is 22 ppb.
Measurements at the National Archives Building in Washington in December
1982 and January 1983 show a grand average of 9 ppb of SO2 inside the building
versus 23 ppb outside at 24th and L Streets, N.W. Hughes and Myers, 1983~. The
Archives Building at present is equipped for coarse particle filtration only, and
Hughes and Myers jl983) concluded that SO2 appears to pass through that air
conditioning system with little or no change.
Nitrogen Oxides
Investigators have examined oxides of nitrogen levels in archives and galleries
that lack chemically protected air conditioning systems. Hackney {1984) found
that NO2 levels inside the Tate Gallery in London were highest in unconditioned
galleries {at values of 15 to 23 ppb) but were lower inside loosely fitting display
cases and unused storerooms {at values of 2 to 3 ppb NOT. This suggests that
enclosing archived documents in proper storage containers may afford significant
protection from NO2 exposure. NOx levels inside the National Archives Building
OCR for page 20
20
PRESERVATION OF HISTORICAL RECORDS
in Washington, measured by Hughes and Myers {1983), showed indoor NOX con-
centrations in the range of 10 to 252 ppb compared with 10 to 527 ppb outside {the
indoor tracking the outdoor) . They concluded that the building ventilation system
did not significantly attenuate outdoor NOX levels. Indoor versus outdoor relation-
ships for NO and NO2 recently have been measured in the newly constructed
Virginia Steele Scott Gallery at the Huntington Library in San Marino, California
{Cass, presentation to the committee, 1985~. Pollutant removal systems at that
site are confined to particle filtration only. Over the period October 30-November
9, 1984, indoor NO averaged 37 ppb compared to 36 ppb outdoors, while indoor
NO2 averaged 38 ppb compared with 44 ppb outdoors. These studies suggest that
indoor NOX concentrations in well-ventilated galleries, libraries, and archives
that lack a NOX removal system will be expected to be close to those outdoors.
Ozone Levels
Ozone is a highly reactive gas and reportedly can be removed almost com-
pletely from the atmosphere of some museum galleries. Thomson {1978) noted
that this is probably due to O3 interaction with interior surfaces Presumably
including the collections). Studies by Shair and Heitner ~ 1974) showed that indoor
ozone levels can be predicted by a simple mathematical model given ozone loss
rate data for various building materials, data on building indoor surface character-
istics, ventilation rates, and whether or not a deliberate pollutant removal system
is present.
A survey of ozone levels inside museums and libraries recently has been
completed in Southern California ;Cass, presentation to the committee, 1985),
from which useful generalizations can be drawn about the ozone level expected as
a function of building design. Buildings with rapid air exchange with the outdoors,
no internal air recirculation, hard interior surfaces, no ozone removal equipment,
and a high volume-to-surface area ratio showed indoor O3 levels 70 percent to 80
percent of the values found outside. Peak 1-hour average ozone levels inside one
such museum in Los Angeles have been observed at 143 ppb compared with 173
ppb outside, or 83 percent of the outdoor level. This is consistent with observed
values in the gallery at the Sainsbury Center for Visual Arts in England, where
indoor O3 levels of up to 40 ppb were observed inside a modern art gallery in the
presence of peak outdoor levels of 58 ppb, or 69 percent of the outdoor level {Davies
et al., 1984~. Southern California galleries with conventional air conditioning
systems, a high internal air recirculation rate, but no ozone removal equipment,
showed indoor ozone levels about one-third that observed outdoors. Buildings
without air conditioning that had little ventilation often showed very low O3
levels (about 10 percent of that outdoors), again due to depletion by reaction with
building surfaces.
Measurements made inside the National Gallery, the Madison Building of the
Library of Congress, and the National Archives Building in winter by Hughes and
Myers ~ 1983) showed undetectable small O3 levels. They attributed this to O3 loss
to interior surfaces and cautioned the reader that conditions during the summer
high-ozone season may be quite different. Indoor O3 levels in the Archives Build-
ing during the summer are unknown but should be investigated before making an
assumption that they are very low.
OCR for page 21
ENVIRONMENTAL CRITERIA
Particulate Levels
21
Most libraries, archives, and galleries currently employ particle filtration
equipment, and therefore particulate levels are reviewed in detail in the following
discussion of pollutant removal systems.
POLLUTANT REMOVAL SYSTEMS
Sulfur Dioxide Removal
Sulfur dioxide removal from building ventilation air has been achieved suc-
cessfully by a variety of means. Hughes and Myers; 1983) showed that application
of a wash system at the East Building of the National Gallery in Washington
reduced SO2 levels to below 1 ppb. At the Madison Building of the Library of
Congress in Washington, a pollutant removal system based on a packed bed of
Purafil {KMnO4 on an alumina support) reportedly reduced SO2 levels below 0.5
ppb Hughes and Myers, 1983~. Hackney jl984) examined SO2 concentrations in
the new extension galleries at the Tate Gallery in London, where the air condition-
ing system employs activated carbon filters. He found that SO2 levels were
reduced to 0 ppb compared with 26 ppb outside on February 4, 1980, and to
between 4 ppb and less than 2 ppb compared with 80 ppb SO2 outside on March 14,
1980.
Nitrogen Oxides Removal
The NOX removal efficiency of acid gas control systems in actual use in the
Washington, D.C., area also has been examined by Hughes and Myers; 1983) . At
the East Building of the National Gallery, a wash system reduced the indoor NOX
levels to the range of 7 to 50 ppb during times when outdoor levels were in the
range of 40 to 92 ppb. In the Madison Building of the Library of Congress, a packed
bed of Purafil for acid gas removal reduced the indoor NOX levels to the range of 4 to
154 ppb in the presence of outdoor levels of 46 to 318 ppb. These data show that the
wash and Purafil systems are much less effective for NOX removal than for SO2
removal, but the reason is not yet clear, since laboratory tests show Purafil to be
effective. Additional research is needed to identify appropriate NO2 removal prac-
tices. These test data should be reviewed to ascertain whether any NO2 measure-
ments were made, as opposed to measurements of total NOX. NO2 and other
species {e.g., HNO3) that are measured as if they were NO2 by chemiluminescent
NOX monitors are the damaging pollutants of interest. It may be that the Purafil
and wash systems are removing much of the NO2 but leaving NO uncollected.
This would contribute to high indoor NOX levels yet provide a low NO2 level
indoors. Therefore, a second set of indoor versus outdoor NO2 measurements
should be commissioned, if necessary, to check indoor NO2 levels explicitly. In
addition, the NO2 removal efficiency of activated carbon or chemically impreg-
nated activated carbon-based pollutant removal systems in actual use should be
examined.
OCR for page 22
22
PRESERVATION OF HISTORICAL RECORDS
Ozone Removal
Activated carbon filtration systems for ozone removal are used by many major
libraries and museums in the Los Angeles area. These include the Huntington
Library, Huntington Library Art Gallery, Los Angeles County Museum, Norton
Simon Museum, I. Paul Getty Museum, and Southwest Museum Library. Indoor
versus outdoor ozone measurements made at the Huntington Library Art Gallery
in midsummer of 1984 showed peak indoor O3 levels of 10 ppb when peak outdoor
levels were 170 ppb, or about 94 percent removal ;Cass, presentation to the com-
mittee, 1985~.
Particulate Matter Removal
Even though most forced ventilation systems contain some form of particle
filtration device, very little literature exists on the detailed effect of these filters on
the chemical and soiling aspects of air quality in archives, libraries, and museums.
Particulate matter concentrations were not measured during the recent examina-
tion of the National Archives Building, the National Gallery, and the Library of
Congress {Mathey et al., 1983~. This lack of data could be perpetuated if the
monitoring procedures outlined by Mathey et al. t 1983) are adopted, because these
procedures involve monitoring the pressure drop across the particle filters rather
than their actual in-use particle removal performance as a function of aerosol size
and composition. If there is no direct examination of the actual measure of particle
breakthrough or indoor aerosol levels, then it is possible to miss the identification
of those particles that are not being collected effectively, or, alternatively, to miss
the fact that particulate matter is being generated indoors.
Particulate air quality control considerations applicable to museums and
other places where irreplaceable materials are stored were discussed by Thomson
{1965, 1978~. A thorough assessment of particle removal systems must take parti-
cle size and chemical composition into account. The size distribution of atmo-
spheric particulate matter usually is bimodal or trimodal, with a coarse particle
grouping consisting largely of soil dust, road dust, and sea salt (particle diameters
of about 1 or 2 ,um and larger); an ultrafine particle mode consisting of freshly
nucleated gas-to-particle conversion products, such as H2SO4 aerosol {in sizes
below 0.1 ~m); and an accumulation-mode aerosol {particle diameter ranging
between 0.1 ,um and 1 or 2 ,um) derived from fresh emissions of combustion
products or the coagulation of ultrafine aerosol plus condensation onto a pre-
existing aerosol. Under polluted urban conditions, the coarse and fine particles
may make comparable contributions to total particle volume {and hence mass)
concentration {see Figure 3-1~. The fine particles, below 1 or 2,um in diameter, are
chemically quite different from coarse dust and may have unique damage poten-
tial because of their high black soot content and potential for contributing acid
aerosols.
Indoor-outdoor particulate matter concentration relationships have been
reviewed {Yokom et al., 1976; Meyer, 1983), and the authors noted that indoor
levels can be greater than or less than those outdoors, depending on ventilation
conditions and on activity levels inside the buildings. An examination was made
of particulate matter concentrations inside and outside the City Hall, a non-air
OCR for page 23
ENVIRONMENTAL CRITERIA
120
100
c,
Q 60
C]
u
> 40
20
o
0.001 0.01
23
Heavy Smog Aerosol
August25, 1983
beat = 5.49 x 10 4m~1
1~.- 550 nm
Visual Range ~ 7.1 km
1 ~-I 1 1
0.1
~ LL
1.0 1 0.0 1 00.0
PARTICLE DIAMETER (,um)
FIGURE 3-1 Size distribution of heavy smog aerosol at Pasadena, California {Larson et
al., 1984~.
conditioned library, two air-conditioned office buildings, and two private homes
in Hartford, Connecticut {Yokom et al., 1971~. Indoor particulate matter levels
relative to those outdoors ranged from 0.16:1 to 1.15:1, with indoor levels less
than those outside in all but one case. For the air-conditioned buildings, the
indoor-to-outdoor aerosol mass ratio ranged from 0.31:1 to 0.75:1. The largest
percentage attenuation of outdoor loadings occurred during winter episodes when
outdoor mass concentrations were high. This observation was explained by noting
that the high-concentration events in Hartford were enriched in large particles
that are removed readily as they attempt to penetrate a building. Both aerosol mass
concentration and the soiling index were monitored during the study, and a greater
attenuation of the aerosol mass concentration than of the soiling index between
outdoors and indoors was found. That observation is consistent with the hypothe-
sis that soot particles contributing to the soiling index values are primarily con-
centrated in the fine particle sizes that may negotiate building air inlets more
readily than coarse particle material. The assessment concluded that indoor-out-
door soiling index ratios in that study did not appear to be significantly different for
air-conditioned versus non-air-conditioned buildings, which indicates that soil-
ing particles were not effectively removed by the filters in the air-conditioning
systems.
Further evidence of the selective alteration of the chemical composition and
size of airborne particulate matter by ventilation systems is illustrated by data
taken at a newly built art gallery in Southern California. The gallery's particle
removal system specifications called for U.L. Class 2 filters, Farr 30/30 or equal,
pleated, strainer mat-type, 2 in. thick. Aerosol mass loading was measured inside
OCR for page 24
24
PRESERVATION OF HISTORICAL RECORDS
and outside of the gallery, and the chemical composition of the aerosol at both sites
was analyzed for ionic species by ion chromatography, for trace elements by X-ray
fluorescence and atomic absorption, and for organic and elemental carbon by
temperature-programmed combustion and pyrolysis. Indoor aerosol concentra-
tions of 30.9 ,ug/m3 were found compared with 79 ,ug/m3 in the outdoor air sup-
plied to the air-conditioning system {Cass, presentation to the committee, 1985~.
Chemical analyses of the indoor and outdoor samples showed 90 to 100 percent
removal of the crustal elements Al, Si, Ca, Ti, Mn, and Fe, indicating excellent
removal of coarse particle soil dust.
Chemical elements characteristically found in fine particle sizes less than
2 am in diameter were removed with very poor efficiency: Pb and Br customarily
associated with automobile exhaust were removed only to a slight extent il9
percent removal and 9 percent removal, respectively). Between 16 percent and 55
percent of the sulfate aerosol was removed by the ventilation system. Total aerosol
carbon particle levels inside were almost identical to total aerosol carbon levels
outside, but black elemental carbon levels indoors were lower than those out-
doors, suggesting an indoor source of aerosol organic carbon. This poor filtration
efficiency for fine particles should be avoided in future designs, since the fine
particle fraction of the outdoor aerosol burden contains much of the black soot and
acidic material.
Fine particle control can be achieved by high-performance filters with or
without simultaneous use of electrostatic precipitators. Thomson {1965) warned
that electrostatic precipitators should not be used in the air-conditioning systems
of museums because of the potential for ozone generation. The NBS study
{Mathey et al., 1983) tended to discount this problem because the O3 levels gener-
ated would be below their recommended indoor air quality standard. Thomson's
jl965) caution is appropriate. The committee considers the NBS O3 air quality
limit to be too high, and experience shows that it is unwise to assume that a carbon
bed used to protect against the deliberate generation of O3 in an electrostatic
precipitator will be working properly at all times.
RECOMMENDED STANDARDS
The critical areas identified for the National Archives indoor air quality con-
trol are covered individually in the following sections.
Temperature and Relative Humidity
The control of temperature and relative humidity is frequently cited as the
first step in environmental control in collections management [Thomson, 1978;
Mathey et al., 1983~. Indeed, the evidence provided by the committee's visit to the
Archives suggests that the resulting benefits are well documented in actual prac-
tice. However, precise temperature and relative humidity standards are less read-
ily identified. The rationale for the lowest temperature of storage consistent with
energy conservation {costs) and worker comfort lies in the Arrhenius relationship
{reaction rate) and its consequence that a reduction in temperature of 10°C
reduces the rate of reaction E.g., oxidation, hydrolysis) by approximately a factor
of 2. The committee is not aware of any data that support precise levels of control
OCR for page 25
ENVIRONMENTAL CRITERIA
25
on either side of the selected temperature. Hence, the committee has specified a
temperature range to be maintained, rather than a single temperature with an
artificially precise level of control about that temperature. No benefits are known
to be derived from controlling a temperature to + 1°F tO.5°C) in contrast to +2°F
{1.1°CJ or even +5°F {2.8°C).
The specification of relative humidity {RH) is more difficult, since higher
levels of RH generally are desirable for materials handling, whereas low RH is
preferable for reduction of biological or chemical attack. iSee Chapter 4 for a
discussion of the effects of temperature and moisture variations on the properties
of paper. ~ Further complications arise in mixed collections that involve leather,
textiles, paper, and photographic materials. The prudent approach appears to
involve the selection of a median RH level of approximately 40 to 50 percent with a
modest level of control, since fluctuations in RH More appropriately equilibrium
moisture content) introduce undesired mechanical stresses. This is especially so
in bound volumes, larger format paper documents, and photographic materials. It
also should be noted that the sensors used for control in active systems E.g., air
conditioning humidity sensors) are notoriously unreliable, so that specified con-
trol is often ephemeral. Here, too, the literature provides little support for benefits
associated with a more precise level of active control than +5 percent RH. The
committee emphasizes its belief that the temperature and relative humidity val-
ues specified should be achieved at the document surface, not simply within the
room air. This suggests greater reliance on the demonstrated buffering capacity of
controlled microenvironments, such as polyester encapsulation and acid-free
boxes, than on active control.
Air Quality
The committee feels that sufficient information exists to demonstrate that
materials like those found in library collections can be damaged if stored in poor
environmental conditions. At the same time, the experimental data needed to
quantify dose-response functions for use in making precise damage predictions do
not exist. For that reason, recommended environmental conditions for storage of
archived materials at present are based primarily on expert opinion. Tables 3-3 and
3-4 summarize the variety of recommendations that have been made.
Evidence that good environmental control will make a significant difference
to the future of the National Archives is provided by a direct inspection of the
present Archives collection by members of the committee who are experts on the
condition of the Library of Congress collection. The Archives first installed its
conventional air conditioning in the 1930s, while the Library of Congress did not
achieve temperature and humidity control in most parts of its collection until the
1960s. The condition of the paper in bound volumes in the Archives at present was
found to be noticeably better than that at the Library of Congress. Furthermore,
the vast majority of the Archives collection traditionally has been housed in file
boxes rather than in bound volumes. The committee's inspection team reports
that the paper records within these boxes are in better condition than the paper
records in bound volumes on the same shelves. Bound materials typically show
evidence of deterioration and aging that progresses into the volumes from the
outer edges of the paper, which are exposed to room air. The paper in boxed
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26
PRESERVATION OF HISTORICAL RECORDS
TABLE 3-3 Air Quality Criteria for Archives, Libraries, and Museums
Authority or Particulate
Installation SOx NOX O3 Removal Required
ANSI-PM Suitable washers or absorbers Preferably HEPA
ASHRAE Canister-type filters or spray washers of chemical 85% DSM
pollutants in outdoor air
BML 0 0 0 0
CCI Should not exceed 10 ppb 95% - 1 ,um
Consider central air purification in high ambient 50% 0.5-1 ,um
areas
LC Purafil system in use 95%
NBS 1 tig/m3 5 ,ug/m3 25 ~g/m3 75 ~g/m3
(0 4 ppb) (2.5 ppb NO2) 113 ppb) TSP 1HiVol)
N-PNB s 10 ,`4g/m3 c 10 ,ug/m3 c2 ~g/m3 High-rating DSM
ROM-C Charcoal or equivalent filtration to remove SOx, 99% - 10 ,um
NOx' O3 95% 21 Em
T c10 ~g/m3 c10 ~g/m3 0-2 ~g/m3 60-80% MET
ANSI-DSP cl ~g/m3 N.S. c2 ~g/m3 See Table 3-4
{0.4 ppb) (1 ppb)
KEY: ANSI-PM = American National Standards Institute-Photographic Standards; ASHRAE =
American Society of Heating, Refrigeration, and Air Conditioning Engineers; BML = British
Museum Libraries; CCI = Canadian Conservation Institute; LC = Library of Congress (Madison
Building); NBS = National Bureau of Standards; N-PNB = Newberry Library-PN Banks Planning
Study; ROM-C = Royal Ontario Museum Conference; T = G. Thomson; ANSI-DSP = American
National Standards Institute Practice for Storage of Paper-Based Library and Archival Materials
(Draft 4, 1985~; HEPA = High-Efficiency Particulate Air; DSM = Dust Spot Method; TSP = Total
Suspended Particulates; MBT = Methylene Blue Test; N.S. = No Standard.
SOURCE: After Baer and Banks (1985a).
containers shows minor mechanical damage, mainly at the top edges of files, and
this damage is probably due to repeated handling during searches. The microenvi-
ronment within the boxes appears to protect the records. This is consistent with
{a) the damping of temperature and humidity fluctuations by the box and {b) the
presence of a barrier against pollutant intrusion.
This evidence, plus the realization that the vast majority of the Archives
collection will remain on paper for the foreseeable future, argues in favor of the
committee's endorsement of both the draft ANSI standard, Practice for Storage of
Paper-Based Library and Archival Materials, and the suggested NBS standards for
proposed environmental control in archives. Where the two sets of recommenda-
tions are in conflict, the more restrictive requirement is endorsed {e.g., the pro-
posed ANSI recommendations for O3 and particulate matter). The NBS
recommendations for particulate matter are derived from ASHRAE recommenda-
tions, which are based largely on human occupancy requirements. These require-
ments could be met without providing any significant protection from much of
the fine black particulate matter that would cause a long-term soiling hazard to the
Archives. On the other hand, the ANSI standards reflect the committee's concem
that these fine particles are detrimental and should be removed. At present, the
majority of the experts cited in Tables 3-3 and 3-4 view ozone as being at least as
hazardous to many materials as is NOx. Therefore, it can be concluded that the
concentration objectives for the gaseous pollutants {e.g., SO2, NO2, 03) should be
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ENVIRONMENTAL CRITERIA
TABLE 3-4 Draft ANSI Particulate Standards for
Paper-Based Documents in Libraries and Archives
ASHRAE ASHRAE
System Weight Atmospheric MIL-STD
Filter Arrestance Dust Spot 282 DOP
Location Efficiency Efficiency Efficiency
Prefiltera -80% 230% -5%
Intermediate
filterb 2 95% - 80% 2 50%
Fine
filterb N.A. 2 90% 2 75 %
aFor outside or makeup air.
bFor supply (both outside and recirculated] air.
KEY: DOP = Dioctyl phthalate; N.A. = Not applicable.
SOURCE: After Baer and Banks l1985b).
27
controlled to the same general order of magnitude. The committee's suggested
standards are given in Table 3-5.
For the Archives inventory, these environmental conditions need only be
achieved at the surface of the documents. The Archives file boxes provide a micro-
environment that probably helps to damp temperature and relative humidity
fluctuations and also probably attenuates pollutant intrusion into the box. A study
is needed of the transfer coefficients that relate ambient conditions in the Archives
stack areas to conditions inside the boxes. Much of the intended environmental
protection apparently can be provided by passive control (e.g., the laoxes) rather
than by complete reliance on expensive active control measures {e.g., air condi-
tioning).
On the average, an individual page within the Archives collection is likely to
be retrieved, consulted, or made use of less than once every 100 years. In view of
this, the cost advantages of passive environmental control could be extended by
placing much of the Archives collection in remote low-temperature storage {e.g.,
underground vaults) outside the city of Washington. These vaults could be
TABLE 3-5 Recommended Standards for
Paper-Based Records in a Mixed Collection of
Bound and Unbound Materials {Standards to be
Met at the Surface of the Records)
Environmental Variablea
Temperature
Relative humidity
so2
NO2, HNO3
o3
Particulates
Control Level
68-72°F
40-50%
< 1 ~g/m3 (0.4 ppb)
Best available technology
<2,ug/m3(1ppb)
Same as Table 3-4
aSpecifications are averages over a 24-hour period. Small, short-
term excursions outside these limits are permitted.
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28
PRESERVATION OF HISTORICAL RECORDS
selected so that they present a lower air-conditioning and pollutant removal load
than that required at the Archives Building, which is located in the city center.
Monitoring for Indoor Air Pollutant Objective Compliance
For the gaseous pollutants, S02, 03, and NO2, ambient measurements can be
taken either by manual methods, in which an integrated sample is collected over a
period of hours or days, or by use of continuous-monitoring instruments. Manual
methods usually involve drawing an air sample through an appropriate liquid
reagent, followed by calorimetric determination in the laboratory. Standard man-
ual methods for SO2, NO2, oxidants, and many other gaseous pollutants are
described by the Intersociety Committee 1977.
Continuous-monitoring instruments for S02, 03, and NO2 are customarily
used for monitoring pollutant levels in outdoor air. Routine ambient monitoring
systems in the Los Angeles area employ pulsed fluorescent SO2 monitors, chemi-
luminescent NO/NO2/NOX monitors, and ultraviolet photometric O3 monitors.
These instruments operate without consuming wet chemical reagents and spe-
cialized gases. Instruments that operate by other equivalent methods are avail-
able.
A potential difficulty with most of the standard manual methods and continu-
ous instruments on the commercial market today is that these systems were not
designed to measure pollutants at the very low levels specified by the proposed
ANSI or NBS objectives described earlier. The lower detection limit of the standard
manual methods {typically 5 to 10 ppb) might be reduced by drawing larger vol-
umes of air through the absorbing reagent, but this should be done only if the
absorption efficiency of the system at that altered flow condition is confirmed.
Review of specification sheets supplied by several manufacturers of continu-
ous-monitoring instruments shows detection limits as listed in Table 3-6. It will
be noted that the minimum detection limits listed for O3 and SO2 are slightly
higher than the proposed ANSI standards. These detection limits appear to be
close enough to the stated objectives that a rational approach might well be first to
design the building air conditioning system to meet the air quality objectives and
then to monitor for equipment failure by determining whether pollutant levels
exceed instrumental detection levels similar to those given in Table 3-6. If
research into the effectiveness of storage boxes shows that pollutant levels in room
air can be increased, then the minimum detection limits of present monitoring
systems may cease to be a concern.
The proposed ANSI standards for particulate matter filtration are based on
current ASHRAE test methods that can be used to determine that new filter media
are performing as expected. Monitoring the system pressure drop should be suffi-
cient to discover clogged filters that need to be replaced. In addition, particulate
matter concentration measurements should be made in the archival storage areas,
thereby guarding against the presence of unexpected indoor sources of particulate
matter. Given the stringent filtration conditions in the proposed ANSI standards,
indoor particle levels would be expected to be very low. If monitoring shows that
this is not so, then the origin of the unexpected aerosol material should be investi-
gated. Chemical analysis of the collected filter samples often can be used to
identify the likely source of airborne particulate matter.
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ENVIRONMENTAL CRITERIA
TABLE 3-6 Detection Limits of Continuous-
Monitoring Instruments
Minimum
Detection
Pollutant Measurement Method Limit
.
O3 Ultraviolet photometric 2 to 3 ppb
SO2 Pulsed fluorescent 2 ppb
NO2 Chemiluminescent 2.5 ppb
29
In addition to selection of measurement methods, a decision must be made
either to monitor building pollutant removal system performance continuously or
to check indoor air quality at periodic intervals. The continuous-monitoring
approach probably would require having a skilled air monitoring technician on the
National Archives staff to maintain the equipment. Alternatively, the monitoring
equipment might be maintained by arrangement with other local government
agencies that currently operate continuous ambient monitoring systems for out-
door air quality. If staffing a continuous-monitoring system proves to be impracti-
cal, then an outside consulting firm might be employed. Its task would be to
survey both indoor pollutant levels and the condition of absorbent materials
extracted from pollutant removal system beds at periodic intervals {quarterly or
semi-annually), thereby determining when the pollutant removal system materi-
als must be renewed.
Other Considerations
Damage to organic matter Paper, film, tape, etc.) from rodents, termites,
fungus, and bacteria has been effectively controlled by limiting access to the
storage areas and maintaining effective environmental controls in these areas.
Damage from exposure to light is not a factor in the case of documents with-
out intrinsic value. In most libraries, there is a minimum of direct sunlight, and
artificial light has very little, if any, of the wavelengths in the ultraviolet ~UV)
range that are detrimental to organic inks and dyes {H. H. G. Tellinek, presentation
to the committee, 1985~. Furthermore, these documents are not customarily
placed on public display, so their exposure to any kind of light is likely to be
minimal. Light exposure does present something of a problem for records having
intrinsic value, which are outside the purview of this study.
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OCR for page 32
Record storage stacks showing odder style of government filing system that
required documents to be folded. The NationaJArchives is currently
refiling these records in covered box storage.
Representative terms from entire chapter:
national archives
