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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

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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

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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.

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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.

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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

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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

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ENVIRONMENTAL CRITERIA 1 Bound volumesin storage stacks at the NationaJArchives. Leatherand cloth, as wed as paper, pigments, andinks, are affected by environmental conditions.

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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

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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

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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.

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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.

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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

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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

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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 10C 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

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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 + 1F tO.5C) in contrast to +2F {1.1CJ or even +5F {2.8C). 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 68-72F 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. REFERENCES Baer, N. S., and P. N. Banks. 1985a. Indoor air pollution: Effects on cultural and historic materials. Int. J. Museum Manage. Curatorship, 4:9-20. Baer, N. S., and P. N. Banks. 1985b. Particulate standards for museums, libraries, and archives. 78th Ann. Meet. Air Pollut. Control Assoc. Preprint 85-8.8. Bogarty, H., K. S. Campbell, and W. D. Appel. 1952. The oxidation of cellulose by ozone in small concentrations. Text. Res. J., 22:81-83. Brysson, R. S., B. J. Trask, J. B. Upham, and S. G. Booras. 1967. The effects of air pollution on exposed cotton fabrics. J. Air Pollut. Control Assoc., 17:294-298.

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30 PRESERVATION OF HISTORICAL RECORDS Carey, W. F. 1959. Atmospheric deposits in Britain-A study of dinginess. Int. J. Air Pollut., 2: 1-26. Carroll, J. F., and J. M. Calhoun.1955. Effect of nitrogen oxide gases on processed acetate film. J. Soc. Motion Pict. Telev. Eng., 64:501-507. Cass, G. R., M. H. Conklin, J. J. Shah, J. J. Huntzicker, and E. S. Macias. 1984. Elemental carbon concentrations: Estimation of an historical data base. Atmos. Environ., 18: 153- 162. Committee on Medical and Biologic Effects of Environmental Pollutants. 1977. Ozone and Other Photochemical Oxidants. Washington, D.C.: National Academy of Sciences. Davies, T. D., B. Ramer, G. Kaspyzok, and A. C. Delany.1984. Indoor/outdoor ozone concentrations at a contemporary art gallery. J. Air Pollut. Control Assoc., 31:135-137. Environmental Protection Agency. 1971. Primary and Secondary Air Quality Standards. Fed. Reg. 36:22388-22392. Environmental Protection Agency. 1978a. Air Quality Criteria for Ozone and Other Photochemical Oxidants. EPA-600/8-78-004. Research Triangle Park, North Carolina: U.S. Environmental Protection Agency. Environmental Protection Agency. 1978b. National Air Quality Standard for Lead. Fed. Reg. 36:46245-46277. Environmental Protection Agency. 1979. Revisions to the National Ambient Air Quality Standard for Photochemical Oxidants. Fed. Reg. 44:8201-8233. Environmental Protection Agency. 1982a. Air Quality Criteria for Particulate Matter and Sulfur Oxides, Vol. III. EPA-600/8-82-029cF. Research Triangle Park, North Carolina: U.S. Environ- mental Protection Agency. Environmental Protection Agency. 1982b. Air Quality Criteria for Oxides of Nitrogen. EPA-600/ 8-82-026. Research Triangle Park, North Carolina: U.S. Environmental Protection Agency. Hackney, S. 1984. The distribution of gaseous air pollution within museums. Stud. Conserv., 29:105-116. Hancock, R. P., N. A. Esmen, and C. P. Furber. 1976. Visual response to dustiness. T. Air Pollut. Control Assoc., 26:54-57. Henn, R. W., D. G. Wiest, and B. D. Mack. 1965. Microscopic spots in processed microfilm: The effect of iodine. Photog. Sci. Eng., 9:3, 167-173. Hudson, F. L. 1967. Acidity of 17th and 18th century books in two libraries. Pap. Technol., 8: 189- 190. Hughes, E. E., and R. Myers.1983. Measurement of the Concentration of Sulphur Dioxide, Nitrogen Oxides, and Ozone in the National Archives Building. NBSIR 83-2767. Washington, D.C.: National Bureau of Standards. Intersociety Committee on Methods of Air Sampling and Analysis. 1977. Methods of Air Sampling end Analysis, Second Edition, M. Katz, ed. Washington, D.C.: American Public Health Associ- ation. Larson, S. M., G. R. Cass, K. J. Hussey, and F. Luce. 1984. Visibility Model Verification by Image Processing Techniques. Environmental Quality Laboratory Report. Pasadena, California: Cali- fornia Institute of Technology. Mathey, R. G., T. K. Faison, and S. Silberstein. 1983. Air Quality Criteria for Storage of Paper-Based Archival Records. NB SIR 83-2795. Washington, D.C.: National Bureau of Standards. McCamy, C. S. 1964. Inspection of Processed Photographic Record Films for Aging Blemishes. National Bureau of Standards Handbook 96. Washington, D.C.: National Bureau of Standards. Meyer, B. 1983. Indoor Air Quality. Reading, Massachusetts: Addison-Wesley. Morris, M. A.1966. Effect of Weathering on Cotton Fabrics. Bulletin 823. Davis, California: Califor- nia Agricultural Experiment Station. Newill, V. A. 1977. Air quality standards. Air Pollution, Third Edition, Vol. V, A. C. Stern, ed. Ne~v York: Academic Press. Parker, A.1955. The destructive effects of air pollution on materials. Proceedings of the 22nd Annual Conference, National Smoke Abatement Society, Bournemouth, England, September 28, 1955. Brighton, England: National Smoke Abatement Society. Rowe, F. M., and K. A. Chamberlain. 1937. Fading of dyes on cellulose acetate rayon. J. Soc. Dyers Colour., 53:268-278. Salvin, V. S. 1969. Ozone fading of dyes. Text. Chem. Color., 1:245-251. Salvin, V. S., and R. A. Walker. 1955. Service fading of disperse dyestuffs by chemical agents other than the oxides of nitrogen. Text. Res. J., 25:571-585.

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ENVIRONMENTAL CRITERIA 31 Salvin, V. S., W. D. Paist, and W. J. Myles. 1952. Advances in theoretical and practical studies of gas fading. Am. Dyest. Rep., 41:297-302. Shair, F. H., and K. L. Heitner. 1974. Theoretical model for relating indoor pollutant concentrations to those outside. Environ. Sci. Technol., 8:444-451. Shaver, C. L., G. R. Cass, and J. R. Druzik. 1983. Ozone and the deterioration of works of art. Environ. Sci. Technol., 17:748-752. Spedding, D. J., and R. P. Rowlands. 1970. Sorption of sulphur dioxide by indoor surfaces. I: Wallpa- per. J. Appl. Chem., 20:143-146. Spedding, D. J., R. P. Rowlands, and J. E. Taylor.1971. Sorption of sulphur dioxide by indoor surfaces. III: Leather. J. Appl. Chem. Biotechnol., 21:68-70. Thomson, G.1965. Air pollution-A review for conservation chemists. Stud. Conserv., 10: 147-167. Thomson, G. 1978. The Museum Environment. London: Butterworths. Walsh, M., A. Black, A. Morgan, and G. Crashaw.1977. Sorption of SO2 by indoor surfaces including carpets, wallpaper, and paint. Atmos. Environ., 11: 1107- 1111. Weyde, E. 1972. A simple test to identify gases which destroy silver images. Photog. Sci. Eng., 16:4, 283-286. Yokom, J. E., andG. F. Grappone.1976. Effects of Power Plant Emissions on Materials. EPRIEC-139. Palo Alto, California: Electric Power Research Institute. Yokom, J. E., W. L. Clink, and W. A. Cote. 1971. Indoor/outdoor air quality relationships. J. Air Pollut. Control Assoc., 21:251-259. Yokom, J. E., W. A. Cote, and F. B. Benson. 1976. Effects on indoor air quality. Air Pollution, Third Edition, Vol. II, A. C. Stern, ed. New York: Academic Press. Zeronian, S. H. 1970. Reactions of cellulosic fabrics to air contaminated with sulfur dioxide. Text. Res. J., 40:695-698. Zeronian, S. H., K. W. Alger, and S. T. Omaye. 1971. Reactions of fabrics made from synthetic fibers to air contaminated with nitrogen dioxide, ozone or sulfur dioxide. Proceedings of the Second International Clean Air Congress, H. M. Englund and W. T. Beery, eds. New York: Academic Press.

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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.