Volume 7, Number 5
Nov 1983

Cleaning the Indoor Air

Sulfur dioxide as an air pollutant has been repeatedly named as a chief cause of decay in leather and paper, beginning in 1843 with Faraday's work on leather decay. Along with nitrogen oxides and ozone, it has an especially destructive effect on photographic materials. Yet removal of pollutants from air in libraries and archives was not advocated as a preventive measure until 50 years ago. It was about that time that central heating and the car were becoming significant sources of pollution, and industrial use of hydrocarbon fuels was an important and growing factor.

A 1933 study at the National Bureau of Standards¹ showed that sulfur dioxide "was not completely removed from the air by washing it with untreated water in an air-conditioning system of the usual type. Effective elimination was obtained, however, on washing the air with [alkaline water at] pH 8.5 to 9.0." The Folger Shakespeare Library installed an alkaline-wash system in the 1930s but according to report, it required more maintenance than the library was able to give it consistently, so it was later removed. The National Archives also had one for a few years.

Removal of pollution from the air is not widely advocated even now, although in many locations it could make more difference for preservation than control of temperature and humidity. Today there are three principal methods of indoor pollution control, all of which involve an installation in the air circulation system, in addition to temperature and humidity controls and dust filters: a plain water spray, activated charcoal filters, and activated alumina filters. It is hard to gather information on how many institutions of different sorts use the different methods because there seems to be no central agency keeping track of air cleaning practices, and within a given building few people can identify the person in charge of their own system. The picture seems to be, though, that libraries and archives seldom use any method at all. Museums often use air washing with a water spray. Activated charcoal or alumina are used in hospitals, hotels, industrial plants and other buildings to control infection, odors and corrosion of electrical equipment, as well as in self-contained vehicles and other environments where air must be recycled.

So far four libraries are known to be using the activated alumina filter system marketed by Purafil, Inc. (P0 Box 80434, Atlanta, GA 30366): the Library of Congress (in its Madison Building), the Newberry Library (in its new addition), El Prado in Madrid and the National Library in Venezuela. They have used it only in new buildings.

The four other research libraries now using NEH grants to install climate control systems (AN March 1983, p. 11) are not known to be filtering out anything beyond ordinary dust. However, the National Archives and Records Service (NARS) is having a state-of-the-art climate and pollution control system designed for its original building on Pennsylvania Avenue by the National Bureau of Standards (AN March 1983, p. 10). Neither NBS nor MARS has announced yet what method will be used to purify the air.

The activated alumina system consists of a filter bed of alumina pellets impregnated with potassium permanganate and other reactive agents. The pellets work by adsorption and controlled oxidation, and are able to remove a large number of gases from the air. Sulfur is bound on the surface of the pellets in compounds with potassium or magnesium, or is retained in the pellet as elemental sulfur. Ozone is broken up and used in the oxidation of other gases. Eventually, like activated charcoal, the pellets are used up and have to be changed. The system calls for sophisticated monitoring techniques and is expensive to install, but can result in fuel savings, because it permits more recycling of indoor air and less dilution with hot or cold outdoor air. In addition, it results in long-tern savings in the acquisitions and various processing budgets, because it extends the life of the materials on the shelves.

One of the best sources, if not the best, on the nature, effect and control of air pollution within buildings, is Garry Thomson's The Museum Environment (Butterworth's, Boston, 1978). It is not just for museum conservators, or for specialists. The first half is easy reading, being addressed to the reader without much background in science, while the second half covers the same ground in greater technical detail, for readers who want the whole story. Activated alumina filters were just coning into use when this book was being written, so they are not mentioned. In fact, Thomson gives little or no detail on specific commercial control systems, but a great deal of the background one needs for understanding the job they have to do.

1. Arthur E. Kimberly and Adelaide L. Emley. Study of Removal of Sulfur Dioxide from Library Air. U.S. Dept. of Commerce, Standards Bureau, Misc. Publication 142. Washington, DC: USGPO, 1933.