Volume 5, Number 1, March 1983, pp.2-3

Ozone: an Invisible Menace

The Conservation Center of the Los Angeles County Museum of Art, in conjunction with the Environmental Quality Laboratory/California Institute of Technology, has begun a long-term study of the effects of air pollution on works of art and artists' materials. The conservation literature has little to offer on the effects of ozone on artists' materials. Generally, it is discussed as being a very powerful oxidant, which it certainly is, but little direct evidence is given. The works of Salvin³ Lebensaft and Salvin², and Haylock and Rush³ have exhaustively documented the ozone fastness of the commercial dyes Disperse Blue 3 and Disperse Blue 7. But in terms of artists' materials, this work only suggests to the researcher that anthraquinones used in artists' pigments might be adversely affected.

As the first phase of our study, an investigation of the effects of ozone on watercolors has been carried out, and two papers are currently being written on the results of those experiments. ^4,5 A brief discussion of these results is given below followed by the results of an investigation of ozone concentrations within buildings using a mathematical model.

It was decided to systematically investigate watercolors, specifically Winsor & Newton, and gauge which tube colors were not fast to ozone. On the basis of the pigment makeup of each tube, we could then make rough estimates of which components were changing. Color evaluation was based upon three independent methods: Munsell Color matching, a Macbeth Color Reflectance Densitometer, and a multi-spectral reflectance spectrophotometer. The results of these investigations by Shaver, Case, and Druzik⁴ as well as Driskov, Case, and Druzik⁵ indicate that four general classes of color change occur:

1. Fading due to the destruction of the chromophore in the principal dye of the pigment.
2. Color shifts which the observer sees as a change of hue more than fading (although fading occurs).
3. Metameric fading which goes undetected under some light sources.
4. Metameric color shifts which can be caused by the oxidation of a component in the tube color.

In The Museum Environment, Garry Thomson⁶ points out that due to ozone's extremely high reactivity, its lifespan within a building is very short, lasting but minutes. He suggests that it may not be as big a factor indoors as other pollutants. Yet, he further indicates more work is needed on this specific pollutant. On the other hand, Sabersky, Sinema, and Shair⁷ have measured indoor ozone at concentrations 65% +/- 10% of the outside levels. This is, without a doubt, an unsatisfactory condition which needs some resolution.

As a result, I took the mathematical model relating indoor pollutant concentration to those outside, as offered by Shair and Heitner⁸, and wrote a program which permitted testing of the model for the TRS-80 microcomputer. This program allowed me to create different types of buildings. By altering the internal volume, interior surface area, building materials, unfiltered infiltration air, air conditioning filtered make-up air and the efficiency of the air conditioning filter, I could create any type of air pollution condition within a building and measure the minute by minute adjustment to its ozone concentration.

I first checked the validity of the model with actual measured concentrations. The results showed good agreement; so I began. My buildings ranged from 1000 to over a million cubic feet. They were internally coated with plywood walls, nylon carpeting, cotton, linen, aluminum, glass, and plexiglas. I provided everything from no air conditioning to good air quality control. There were leaky buildings with high air infiltration rates as well as tightly sealed ones.

The results are interesting. They are summarized below:

1. Small buildings can control their interior ozone, concentrations better than large ones of the same design.
2. Buildings with more organic materials will tend to have relatively fast ozone decomposition values compared to buildings with a greater amount of aluminum, glass, or Lucite.
3. Buildings which offer poor protection are those with a large natural air flow and those with air conditioning systems with high make-up and low filtration efficiency oxidants.
4. Interior building materials may show a reduction in their ability to react with ozone as they age, thus allowing interior concentrations higher than would normally be expected.
5. Depending on the effectiveness of overall air quality measures, some buildings will never have a significant ozone problem while others can expect levels easily as high as 60% the outside level, and this condition may not be eliminated without major structural alterations.

This study showed that ozone concentration is a significant factor to consider in future studies of air pollution within buildings. Fading and the many other manifestations of oxidation to organic materials can and do occur even under the most stringent light control measures. In fact, ozone attack, particularly on conjugated double bonds, may also occur in the dark.^1,2

References

1. Salvin, V., "The Effect of Atmospheric Contaminants on Lightfastness", J. Soc. Dyers and Colorists, 79, 687-696, 1963.

2. Lebenstaf, W., Salvin, V., "Ozone Fading of Anthraquinone Dyes on Nylon and Acetate", Textile Chemist and Colorist, V.4, No. 7, 1972.

3 Haylock, J., Rush, J., "Studies on the Anthraquinone Dyes on Nylon Fibers", Textile Research Journal, January 1976.

4 Shaver, C., Case, G., Druzik, J., Manuscript in preparation.

5 Drisko, K., Case, G., Druzik, J., Manuscript in preparation.

6 Thomson, G., Museum Environment, Butterworth, I.I.C., 1978.

7 Sabersky, R., Sinema, D., Shair, F., "Concentration Decay Rates, and Removal of Ozone and their Relation to Establishing Clean Indoor Air", Environmental Science & Engineering, Vol. 7, No. 4, April 1973 pg. 347-353.

8 Shair, F., Heitner, K., "Theoretical Model for Relating Indoor Pollution Concentrations to Those Outside", Environmental Science Technology, Vol. 8, No. 5 May 1974, pg. 444-451.