Volume 7, Number 3, Sept. 1985, pp.3-9

Ozone: The Intractable Problem

"Ozone in Air Reported Up; Lead in Decline" New York Times News Service WASHINGTON - Ozone levels increased sharply in the United States in 1983 because of greater industrial activity combined with hot, dry weather, according to a report issued Thursday by the Environmental Protection Agency.

The 12 percent rise in ozone concentration was the only large increase found for the six air pollutants identified by Congress in 1970 as threats to human health.

"...Ozone, which causes respiratory problems, is proving to be one of the more intractable air pollution problems, officials for the environmental agency said.

Abstract:

Ozone's impact on materials has been studied directly for the last thirty years. It has been shown to deteriorate the useful life of many materials such as natural rubber, it fades dyes on nylon and acetate, and participates in the chemistry of corrosion. In addition ozone has been shown to fade many of the natural dyes and dye-based pigments used by artists. Contrary to what was once thought, ozone can be a significant pollutant indoors; however there are means to control it and protect valuable cultural properties.

Ozone, until recently, has received less attention than many pollutants no doubt because it is invisible and its detection is difficult at low levels. On the other hand, sulfur dioxide and sulfate particulates have received plenty of research attention because they are either visible and produce acidic products, or they sorb directly onto paper, leather, or organic coatings. Additionally, nitrogen dioxide has produced a notorious record of dye fading on acetate, triacetate, viscose rayon and cotton, and has caused yellowing in white acetate-nylon blends. Hygroscopic nitrates have been the major cause for stress corrosion failure of nickel brass springs in telephone switching devices in Los Angeles. Recently nitric acid has been recognized as a problem equal to that caused by sulfur dioxide in the formation of acidic precipitation. Airborne particulates soil clothes, pose significant health effects, have been linked to marble deterioration and can penetrate moderately well-sealed display cases and vitrines. Compared to these agents, ozone's rather low profile has caused us to lag behind in our understanding of its impact on materials and on artists' materials in particular. Looking at past literature, we can see a rapidly accumulating body of information on this powerful oxidizing agent, and an alarming record for materials damage. The purpose of this article is to present a general overview on ozone's formation, its attack on materials and penetration into homes, galleries and art museums. While some technical discussions are unavoidable, the known picture will be presented in a form suitable both to the conservator and the conservation scientist.

Formation of Ozone

Ozone (O₃),rather than being a primary pollutant released directly into the air, is produced as a secondary reaction product through the combined interactions of sunlight, oxygen, oxides of nitrogen and hydrocarbons₁. For this reason it can not be simply legislated out of existence.

Over the years more than fifty chemical reactions have been needed to fully describe the formation of ozone in urban atmospheres. However the three most important reactions begin with [i] the photolysis of nitrogen dioxide (NO₂) to form nitric oxide (NO) and atomic oxygen (O); [ii] the formation of ozone by the rapid reaction between atomic oxygen and molecular oxygen (O₂); and [iii] the encounter of ozone with a molecule of nitric oxide which decomposes into molecular oxygen and oxidizes the nitric oxide back to nitrogen dioxide. Most oxides of nitrogen evolve principally as nitric oxide and in the absence of competing reactions the net effect is the destruction of nitrogen dioxide as quickly as it is produced. Nitric oxide concentrations would greatly exceed nitrogen dioxide and ozone would also be quite low in concentration. However, the decomposition of atmospheric hydrocarbons generates free radicals which can convert NO and NO₂ without consuming ozone. This interaction interrupts the simple three reaction process mentioned above. Thus the ratio of NO₂ to NO increases and ozone concentrations also climb. In the Los Angeles area for example, ozone concentrations above 0.20 ppm for one hour are experienced on more than 100 days in a typical year.

Very small quantities of ozone are produced in unpolluted air at ground level, however in industrial areas the maximum level of secondary ozone which is produced at midday can easily reach several orders of magnitude above the normal background level. In addition, regions lying either adjacent to or within the wind trajectory paths of urban population centers can find that 24 hour integrated ozone levels are only slightly below their urban counterpart. Supporting this downwind phenomenon, Kauper and Niemann^2,3 conducted two studies to characterize interbasin pollutant transport. Their studies used extensive monitoring methods involving the use of aircraft, surface vehicles and ships for data to calculate the movement of "air parcels" as they drifted from Los Angeles over water to downwind locations. They concluded that high ozone levels in Oxnard during June and July 1975, and in San Diego during October 1976, were the result of ozone transport aloft. Recent measurements taken at the J. Paul Getty Museum located in Malibu just north of Los Angeles, have shown that this oceanside area which has traditionally been considered to have low levels of ozone, has values reaching 0.20 ppm. Since ozone is clearly one of the most powerful oxidizers in nature, these studies indicate that these levels will have a profound effect on damage to materials in regions neighboring communities with significant ozone levels.

Materials Damage: Polymers

Chain breaking and crosslinking can both occur in polymers exposed to ozone. The reaction of ozone with olefinic compounds is well understood and today the Criegge electrophillic attack mechanism is universally accepted⁴. One of the most dramatic examples of this reaction has been that of ozone's attack on natural rubbers. For a while this information was used for semi- quantitative tests for ozone. In these instances the regular open conjugated structure of cis-1,4 polyisoprene is easily oxidized and depolymerized to levulinic acid. Jaffe noted that without the inclusion of antioxidants, rubber cracking under stress can readily be detected within 3/4 hours when exposed to ozone levels as low as 0.03 ppm. He further states that the important factors influencing the action of ozone on rubber include: [i] degree of stress, [ii] nature of the rubber compound, [iii] concentration of ozone, [iv] period of exposure, [v] velocity of ozone contacting the rubber, and [vi] temperature⁵. Even with the addition of the antioxidant, diphenyl ethylene diamine, problems are only postponed until this product is volatized out. Interestingly, rubberized cotton garments are seen to yellow as the antioxidant migrates outward forming a yellow nitroso compound caused by an interaction with nitrogen dioxide. It is useful to compare this 0.03 ppm ozone level to levels of 0.2 to 0.3 ppm which have been measured in such diverse locations as Detroit, Houston, Los Angeles, New Haven, Sydney and Toronto.

In general saturated polymers such as polyethylene are relatively inert to ozone's effects. However double bonds within polymers which have a high degree of saturation may find that after the initial ozone attack, normal oxidation can then proceed more easily⁶. Katai et al. studied the attack of ozone on cellulose and related substances and found evidence for a twofold mechanism⁷. The first mechanism is indiscriminate as to the site of attack and forms a number of differing groups with kinetic chain lengths of over 100. In this instance atmospheric oxygen was an important reactant since ozonolysis in nitrogen proceeded only until all ozone was consumed. The second mechanism seems to be similar to acid-catalyzed hydrolysis in that chain degradation occurs. However, this ozone-catalyzed hydrolysis is not pH dependent and was observed to happen even in neutral pH solutions. It seems clear that polymers derived from the cellulose or cellulosic materials which are important in conservation (i.e. methyl and carbomethyl cellulose) might also show a vulnerability. Both modified and unmodified starches might also be suspected to behave in a similar manner.

A research group at the Environmental Quality Laboratory at the California Institute of Technology has found that the coloring agent in tumeric (curcumin), is almost totally destroyed in ozone test exposure studies⁸. Curcumin is essentially made up of two coniferyl alcohol molecules joined tail to tail. This deterioration suggests that other similar methoxy-hydroxy- phenolic propanes (guaiacylpropanes) which are the principal building blocks of lignin, may equally be prone to attack. If this conjecture is true, and there is no evidence that it is not, lignin in groundwood papers, linens, particle boards, etc. are probably attacked at an even higher rate than cellulose might be. A further theoretical reasoning which suggests that lignin's monomers may be susceptible to ozone degradation is based upon the observation that electron-repelling groups such as alkyl, hydroxyl, methoxyl, and so on, activate the benzene ring for ozone attack¹⁰. Given the large number of photochemical breakdown species from lignin, it is almost certain that many of them would easily undergo further ozone attack. Lastly Bogaty and associates exposed two types of wet cotton fabrics to 0.02 and 0.06 ppm ozone for 50 days and found in both instances there was a 20% loss in tensile strength and an increase in cupraammonium fluidity⁹.

When evaluating the permanence of polymers it should always be kept in mind that the combined action of several pollutants can alter materials that seem reasonably resistant to any one of them. When polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyacrylonitrile, butyl rubber and nylon were exposed to a mixture of sulfur dioxide, nitrogen dioxide and ozone, they each suffered deterioration in strength. The tensile strength of linear polyurethanes was reduced by nitrogen dioxide plus ozone.

No studies have emerged linking ozone as a pollutant to protein degradation. Needles reminds us however of the sensitivity of keratins and silk fibroin to oxidizing agents as they attack the protein main chain and selected amino acid side chains such as tryptophan and tyrosine. In addition,the disulfide bonds in keratins are also susceptible to attack. These disulfide bonds (cystine linkages) are easily oxidized in wool and can change physical properties and dyeing characteristics¹¹. It's been demonstrated that even while hair is growing on an animal, up to 14% of the initial sulfur is lost. Sulfur is liberated as hydrogen sulphide and oxidation produces first sulfurous and then sulfuric acid³⁶. Sadov, Korchagin and Matetsky have suggested that this loss of cystine linkages results in the production of soluble compounds in alkalies. The author feels that the acceleration of this process may serve as a criterion for determining the presence and degree of ozone enhanced oxidation in wool.

Paint systems have also been examined, although not comprehensively. Campbell et al. used electron microscopy and weight reduction to follow the surface erosion of automobile finishes, latex, industrial coatings and oil based house paints under both sulfur dioxide and ozone attack. In general coatings exposed to ultraviolet light tend to show greatest effect from ozone as a pollutant¹².

Nicholson allowed paint films pigmented with zinc oxide, zinc sulfide or titanium dioxide ground in bodied linseed oil to dry in atmospheres of oxygen and with oxygen combined with each of the following: sulfur dioxide, nitrogen, ozone, carbon dioxide, and hydrogen sulfide. Drying was measured by oxygen absorption. Even minute traces of ozone significantly increased the weight more rapidly and enhanced the wrinkling of all paints studied¹³. Nicholson indicates that minute traces of ozone in oxygen were used but his determination of 0.091% by volume (910 ppm) is about 3 to 4 thousand times the expected peak maxima for a highly polluted day. Therefore, while ozone has been implicated in the accelerated aging of paint films, tests have not proven relevant to conservation.

Materials Damage: Dyes, Pigments and Inks

The technique for measuring noxious trace components in urban air existed as early as the late 17th century when Robert Boyle advised the experimentalist to "hang up clothes and silks died with colours..."¹⁴. But it was not until the late 19th century that this kind of experiment was used to test for atmospheric oxidants. The celebrated Russell and Abney Report of 1888 reports that Windsor and Newton's watercolors were exposed to combusted natural gas fumes in a closed wooden cabinet and changed color distinctly⁵ In 1937 the fading of some blue dyes from exposure to nitrogen dioxide was suggested by Rowe and Chamberlain¹⁶. Another culprit began to emerge in 1955 when Salvin and Walker sought to study the fading of disperse dyestuffs caused by chemical agents other than oxides of nitrogen¹⁷. This now famous study examined draperies which had been dyed with NOx resistant anthraquinone blue dyes and exposed for six months to ambient conditions without light in Pittsburgh, PA; Ames, Iowa; and Austin, Tex. No fading was evident with the Pittsburgh samples. These results were as expected, but in Ames, which is an area low in oxides of nitrogen, fading was apparent. Salvin and Walker provided evidence that the causative agent might be ozone. By the early 1960s complaints from consumers in Texas and Florida about the in-service fading of commercial textiles began to appear. Fading could not be traced to failure of lightfastness or to the effects of oxides of nitrogen. This condition was colorfully labeled "Gulf Coast Fading."

Three studies performed in the early 1970s all conclusively show that: ozone was responsible for this fading of blue anthraquinone dyes on nylon and acetates (Salvin 1974 #18, Lebensaft Salvin 1972 #19, Haylock 1973 #20.) The estimated annual costs related to ozone-induced fading of textiles has been estimated by Salvin at about 84 million dollars.

The bridge between the fading of commercial dyes and the possible vulnerability of artists' pigments was made in 1983 when Shavers et al. demonstrated the fading of Alizarin-based watercolors containing 1,2,dihydroxyanthraquinone in the presence of ozone²¹. Drisko, Cass and DRUZIK extended the range of the pigments examined and also found a universal fading among all pigment blends which included alizarin²². At that time it was postulated that the major composition product might be phthalic acid since it had been found in the liquid phase reactions between ozone and 1,2, dimethylanthraquinone. Also found to fade was the blend of triphenylmethane and copper phthalocyanine. Drisko further found that pigments containing BON-arylamide are fairly resistant to ozone; as are the quinacridones and chlorinated copper phthalocyanine greens. Interestingly, carmine, a lake from natural cochineal, showed no definite change in color after exposure even though chemically it is in part a highly substituted anthraquinone. It should be pointed out that carminic acid possesses a carboxylic acid group between a methyl group and a hydroxyl. As such an electron withdrawing group may deactivate this molecule towards ozone. Because of the carmine's resistance to ozone fading, it cannot be easily conjectured whether or not the flavinoid group of dyes are vulnerable. To date, these dyes (which are the most important class of yellow dyestuffs in European textiles) should probably be regarded as being fugitive and therefore should be protected whenever possible. The flavonoids include Weld, Dyer's Broom (see Erratum p.7) Quercitron (Querqus tinctoria L.), and a few related substances such as: Luteolin, Fisetin, Morin, Apigenin, Rhamnetin, Maclurin and Emodin²³. A few indigo dyes from the Forbes Collection which have been provided by the Fogg's Conservation Center, are currently being investigated and appear to be of intermediate permanence.

One material the author was personally interested in investigating was the iron gallotannate inks which are used for the bulk of man's written record in Europe. We know for a fact that many formulations have converted from a rich black to a rust colored brown. Frequently the inks which have remained black have also burned into their paper supports leaving a perforated and weakened condition. It is often thought that the brown inks have been more stable and benign. However it can easily be demonstrated that even these brown inks can be degraded through the action of hydrogen peroxide. A humid microenvironment with a known concentration of hydrogen peroxide will significantly fade iron gall inks on parchment and convert newly prepared black inks on blotter paper to dark brown. In a test performed by Drisko, Cass and Druzik both old and new inks were subjected to 90 days exposure at 0.31 plus or minus 0.12 ppm ozone with a relative humidity of 46% plus or minus 6%. These test materials showed virtually no effects from the exposure²². If ozone does cause iron gallotannate inks to become fugitive, this condition would probably occur under much more humid conditions which would favor the dissolution of ozone into water condensed in the pores of the paper support fibers. Water absorbed into cellulose below a relative vapor pressure of 0.6 (R.H. 60%), forms a multilayered solid solution which is immobile. Above this value water condenses and forms a mobile surface which slides over the solid layer and into which ozone can dissolve and interact. Please note that the author was easily able to locate almost fifty different recipes for the manufacture of this ink. These test results only apply to the recipes which were tested.

As mentioned earlier in this section, the ozone fading bridge which exists between commercial dyes and artists' materials was not secured until the decade of the 80's. It is interesting however to note the findings indicated in an unpublished study conducted in 1953 by the architectural firm of Perrera and Luckman for the Huntington Library and Gallery. This survey entitled, Air Conditioning Survey For the Preservation of Paintings and Books in the Collection of the Henry E. Huntington Library and Gallery was performed in anticipation of the addition of environmental control equipment to the facility. It reports that the Huntington had asked Dr. Haagen-Smit of the California Institute of Technology for his opinion regarding the potential impact of manmade air pollutants on the collections. Haagen-Smit, considered by many to be the father of photochemical air pollution study, prepared an experiment in which he subjected a "watercolor painting" containing yellow and red pigments to concentrated smog for 48 hours.

He reported that the red pigment faded. Unfortunately this experiment failed to record a description of the pigments tested and was not specific about which photochemical oxidant was used in the test. Thirty years later we can now make intelligent guesses about the identity of the pigment used, but the effects of and distinctions between nitrogen dioxide and ozone are still to be determined.

Materials Damage: Metals

Volume 224 in Science on 11 May 1984 carries a report by Graedel, Franey and Kammlott of Bell Laboratories. Their test results indicate that the attack on copper of reduced sulfur gases such as hydrogen sulfide "...can be markedly enhanced both by solar radiation and by the ubiquitous atmospheric ozone, thus indicating that the high rates of corrosion in urban areas are a result of a complex sequence of multicomponent photochemical processes." Previously it had been known that ozone would enhance the oxidation of silver either in a solid state or in an aqueous solution. The same applies to iron. Further, Jaffe reports that damp or wet aluminum reacts with ozone causing corrosion, but he does not reference his source⁵

Ozone Concentrations in Museums

While evidence has increasingly indicated that ambient ozone concentrations are damaging to a wide range of materials, the air pollution and conservation communities were initially unimpressed about the impact of such dangers to commercial materials used indoors. Particularly vulnerable materials were simply replaced. Yocum, in a summary about indoor/outdoor air quality relationships as they pertain to ozone, concludes in a 1983 article, "In summary, one can say with assurances that indoor concentrations of ozone, will almost invariably be significantly less than those outdoors, and that the indoor environment will be an efficient refuge from outdoor exposure to ozone."²⁴ Garry Thomson²⁵ drawing on the work of Derwent²⁶ and Mueller²⁷ similarly concludes that ozone levels inside museums and galleries must be very low due to ozone's high reactivity. But this picture was about to change rapidly.

The location was the California Institute of Technology. In 1973 Sabersky's group had concluded that indoor concentrations of ozone would not be too much lower than that found outdoors. This conclusion resulted from measurements taken in two adjacent campus lab-office buildings. These two buildings' air conditioning systems supplied 100% and 70%, respectively, of the total air requirements. These systems used only unfiltered outside air²⁸. In 1974 Fred Shair and Kenneth Heitner developed a theoretical model for relating indoor concentrations to those outside and they measured a few buildings at Cal Tech²⁹. Almost immediately Hales et al. were reporting on an experimental verification of this "linear combination" model³⁰. Shavers monitored an art gallery and two museums. The two museums each had activated charcoal filtration systems, while the gallery did not. Indoor ozone concentrations in the gallery were reported as being slightly above 50% of the outdoor levels, but no detectable ozone was found in the museums' filtered air because activated charcoal is an efficient filtering medium for ozone. On the east coast a surprising 1977 report on the atmosphere inside the National Archives found larger concentrations of ozone in some areas than the incoming air supply could possibly have produced and yet there was no internal source³¹. However a more extensive follow-up study in the winter of 1983 failed to corroborate these findings³². Working in England, Davies reported 70% plus or minus 10% of the outdoor levels for ozone in a contemporary art gallery in rural England³³. The ventilation system at the gallery was only pumping in external air.

Finally Druzik and Cass systematically recorded the simultaneous indoor/outdoor concentrations in 11 different buildings including museums, art galleries, historic houses and a library. Tests were conducted over a period of 39 days during the summer of 1984³⁴. Their results show that the indoor concentrations could be predicted according to the type of building construction and mechanical air conditioning plants. Table 1 is taken from these findings. Generally it was found that buildings having no environmental controls but which have a high convection rate, either naturally or artificially produced, can be expected to have indoor ozone levels ranging from 49-84% of the outdoor levels. At sites where the ventilation rates were lower, concentration levels are reduced by 7-20%. The most surprising results found by Druzik and Cass were the high indoor ozone concentrations in a newly constructed building which had advanced heating, air conditioning and ventilation systems. Only large particulate filters had been installed and there was no other form of air purification. In this building the indoor levels ranged consistantly from 24-40% of those outdoors. On the other hand, all of the buildings fitted with complete environmental systems which included chemical filtration, showed vanishing low levels when the chemical system was properly maintained. The Shair and Heitner model was applied to all of these structures and was found to agree reasonably well.

The initial underestimation of the quantities of ozone actually present in building structures stems not from ignorance of ozone's reactivity, but rather from not recognizing the building ventilation system as a dynamic process. A single small open door measuring about 16 square feet will permit the diffusion of about 650 cubic feet of air per minute. For example, the Pasadena Historical Society's Fenyes Mansion allows almost 3,800 cubic feet of polluted air to enter the Mansion every minute when the doors, windows and solarium transoms are open. These values are standard ASHRAE estimates for unassisted diffusion and may be higher when ventilation is assisted by wall fans³⁵. At the same time it is very common to find that only 75% of the air in modern buildings is recirculated. The other 25%, called "makeup air", must be drawn in from outside vents. The current trend towards energy efficiency will not reduce this makeup air value, since it is required to keep the static pressure within the building high, to ventilate the bathrooms and areas of high human density, and, as a bonus, to dilute indoor pollutants such as formaldehyde. The question then is rather an issue of ozone removal either through surface decomposition or by chemical filtration.

There is no question concerning ozone's reactivity on common wall surfaces and its ensuing decomposition. In order of descending reactivity are cotton muslin, lamb's wool, neoprene, plywood, nylon, linen and polyethylene. Lucite, aluminum and plate glass have poor reactivity²⁸. So although one might be tempted to consider using reactive wall cover overall concentrations, this solution has a limited benefit if the air flow is high and it is altogether unfeasible if most of the wall space is covered with objects of value. In any case, given that materials age with continuous exposure, the effectiveness of using commercial materials to make a decomposition surface is reduced over time. Rather, the best method of protection is the use of activated charcoal when an air conditioning plant is used for environmental control. When no environmental control exists, the diffusion of ozone to vulnerable surfaces may be limited by using localized solutions. For example, Thomson shows the beneficial values gained from tightly fitted display cases against rapid changes of relative humidity. He shows how display cases reduce the extremes of R.H. fluctuations over daily and seasonal periods. However ozone in urban environments tends to be scavenged at night by NO and has a daily cycle of only several hours. Thus even a moderately leaky case would be effective against ozone. Currently Cass, Druzik et al.²² are planning to investigate the use of display cases and vitrines for this purpose. This investigation should be able to determine whether or not a display case can be modelled in the same manner as an art museum after the model of Shair and Heitner. If so, it should be relatively easy to design and predict display case performance as a protective measure. These designs should contain concentrations of ozone down or below a level of 0.001 ppm. This value would then be at the recommended limit set in the newly proposed ANSI Standard of Banks ⁵

References

(Table 1 follows references)

1. Sienfeld, J.H. Air Pollution and Chemical Fundamentals. New York: McGraw-Hill, 1975.

2. Kauper, E.K., and Niemann, B.L. Los Angeles to Ventura over water ozone transport study. Covina, CA: Metro Monitoring Services, 1975.

3. Kauper, E.K., and Niemann, B.L. Los Angeles to San Diego three dimensional ozone transport study. Metro Monitoring Services, 1977.

4. Criegge, R. Paper presented at the International Ozone Conference. Chicago: Advan. Chem. Ser., 21, 143(1959)

5. Jaffe L.S. "The Effects of Photochemical Oxidants on Materials." J. Air Poll. Cont. Assoc. 17:6, June 1967.

6. Cook, I. " 'Air Pollution' and Aspects of Polymer Degradation." ICCM Bulletin 2:4, 1976.

7. Katai, A.A., and Schuerch, C. "Mechanism of Ozone Attack on Alphamethyl Glucoside and Cellulose Materials." J. Poly. Sci. 4 (1966)

8. This research group was formed by Dr. Glen Cass (Calif. Inst. of Tech.) and James Druzik (Los Angeles County Museum of Art) in 1981 to study the effects of ozone on artists' materials. Since then the work has been extended by a generous grant from the J. Paul Getty Conservation Institute.

9. Bogaty, H; Campbell, K.S.; and Appel, W.D. "The Oxidation of Cellulose by Ozone in Small Concentrations." Tex. Res. J.

10. Bailey, P. Ozone Chemistry and Technology: "Ozone in Organic Chemistry" Sec.l and "Ozonation of Aromatic Compounds" Chap.IV The Franklin Institute Press, 1975.

11. Needles, H.L. "Protein Chemistry for Conservators (Keratins and Silk)." Paper read at AIC Meeting, 1984, Los Angeles.

12. Campbell, G.G.; Schuur, G.G.; Slawikowski, D.E.; and Spence, J.W. "Assessing Air Pollution Damage to Coatings." J. Paint Technol. 46:593.

13. Nicholson, D.G. "Drying of Linseed oil Paint." Indust. and Engin. Chem. 33:9, 1941.

14. Brimblecombe, P. "Air Pollution in Industrialized England." APCA 28:2, 1978.

15. Brommelle, N.S. "The Russell and Abney Report on The Action of Light on Water Colours." Studies in Conservation 9, 1964.

16. Rowe, F.M., and Chamberlain, K.A.J. "The 'Fading' of Dyeings on Cellulose Acetate Rayon - The Action of 'Burnt Gas Fumes' (Oxides of Nitrogen, etc. in Air) on Cellulose Acetate Dyes." J. Soc. Dyers Colorists 53, 1937.

17. Salvin, V.S. and Walker, R.A. "Service Fading of Disperse Dyestuffs by Chemical Agents Other Than Oxides of Nitrogen." Tex. Res. J. 25, 1955.

18. Salvin, V.S. "Colorfastness to Atmospheric Contaminants." Tex. Chem. Color 6:8, 1974.

19. Lebensaft, W.W. and Salvin, V.S. "Ozone Fading of Anthraquinone Dyes on Nylon and Acetate." Tex. Chem. Color 4:7, 1972.

20. Haylock, J.C. and Rush, J.L. "Studies on the Ozone Fading of Anthraquinone Dyes on Nylon Fibers." Tex. Res. J., 1976.

21. Shavers, C.L.; Cass, G.R.; and Druzik, J.R. "Ozone and the Deterioration of Works of Art." Envir. Sci. Tech. 17:2, 1983.

22. Drisko, K.; Cass, G.R.; and Druzik, J.R. "Fading of Artists' Pigments Due to Atmospheric Ozone." Paper read at 77th APCA Meeting, 1984, San Francisco.

23. Hofenk-de Graff, J. and Roelofs, W.G.T. "The Analysis of Flavonoids in Natural Yellow Dyestuffs in Ancient Textiles." Paper read at ICOM Meeting, 1978, Zagreb.

24. Yocum, J.E. "Indoor-Outdoor Air Quality Relationships." J. Air Poll. Cont. Assoc. 32:5, 1982.

25. Thomson, G. The Museum Environment. London: Butterworths, 1978.

26. Derwent, R.G. Ozone Measurement in an Art Gallery. Warren Springs Laboratory CR810(AP), 1973.

27. Mueller, F.X.; Loeb, L.; and Maper, W.H. "Decomposition Rates of Ozone in Living Areas." Envir. Sci. Tech. 7, 1973.

28. Sabersky, R.H.; Sinema, D.A.; and Shair, F.H. "consentrations, Decay Rates, and Removal of Ozone, and Their Relation to Establishing Clean Indoor Air." Envir. Sci. Tech. 7:4, 1973.

29. Shair, F.H. and Heitner, K.L. "Theoretical Model For Relating Indoor Pollutant Concentrations to Those Outside." Envir. Sci. Tech. 8, 1974.

30. Hales, C.H.; Rollinson, A.M.; and Shair, F.H. "Experimental Verification of Linear Combination Model for Relating Indoor- Outdoor Pollutant Concentrations." Envir. Sci. Tech. 8:S, 1974.

31. Hughes, E.E.; Taylor, J.K.; and Burke, R.W. Report of Analysis of the Atmosphere at Several Locations in the National Archives. U.S. Department of Commerce Document #bO000051, 1977.

32. Hughes, E.E. and Myers, R. Measurements of the Concentration of Sulfur Dioxide, Nitrogen Dioxide, and Ozone in the National Archives Building. U.S. Department of Commerce/ National Bureau of Standards, NBSIR 83-2767, 1983.

33. Davies, T.D.; Ramer, B.; Kaspyzok, G.; and Delany, A.C. "Indoor/Outdoor Ozone Concentrations at a Contemporary Art Gallery." JAPCA 31:2, 1984.

34. Druzik, J.R.; Cass, G.R.; and Adams, M.S. "The Measurement and Model Predictions of Indoor Ozone Concentrations in Art Museums." (Unpublished manuscript under revision.)

35. American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE)

36. National Information Standards Organization Z39 Subcommittee (Paul Banks, Chairman). American National Standard Practice for Storage of Paper-Based Library and Archival Documents.

(Museum with both air conditioning and activated charcoal filtration had virtually no ozone in excess of 0.005 ppm. These included the Los Angeles County Museum of Art, Huntington Art Gallery and J. Paul Getty Museum.)

^* Best and worse case operating conditions