When one thinks of IAQ, the health and well-being of people most often comes to mind. However, IAQ is not only a people issue, it is also a materials issue. Just as people can suffer due to poor air quality in a building, many different types of materials can suffer as well.

Many industrial environments contain corrosive contaminants that can destroy expensive computerized process control equipment. These contaminants, if not properly controlled, can bring production to a standstill, resulting in downtime costing tens, if not hundreds, of thousands of dollars an hour. However, computers can be replaced. This cannot be said for the materials and objects being housed in museums, libraries and archives.

In museums and other "preservation environments" there are a number of factors which can cause the degradation of materials and artifacts. Among these are temperature, humidity, particulates, and gaseous contaminants. Of these, gaseous contaminants are the most destructive.

Gaseous Contaminants

While automotive and/or industrial emissions are considered as the largest contributors of the three main contaminant gases found throughout the industrialized world - sulfur dioxide (SO2), ozone (O3), and nitrogen dioxide (NO2) there are also many significant sources of internally-generated contaminants. Materials and activities associated with restoration and conservation laboratories, many artifacts and archival materials, and employees and patrons themselves can contribute to the overall contaminant load in preservation environments.

Although gaseous contaminants are a major worldwide environmental concern, sources of gaseous contaminants, their introduction and migration through museums, and their interactions with artifacts are the least studied and least understood area of concern within museum environments. General reviews of contaminant sources and object vulnerabilities and information and guidelines for gaseous contaminants were scarce until the 1990s.

Control Specifications

The most commonly cited gaseous contaminants and their recommended control levels are shown in TABLE 1 above. Background concentrations and the peak urban levels for these contaminants are listed for comparison. As can be seen, the recommended levels for several contaminants are below the normal background levels and all are below contaminant levels we would expect to encounter in urban environments.

The biggest problem today is not whether specified levels of air quality can be reached, but whether they can be accurately measured to assure compliance with any standards or control criteria. The qualitative identification and the quantitative determination of gaseous contaminants and their concentrations often make stringent demands on monitoring instrumentation and methodologies. Because of this, a growing number of museums have turned to environmental classification via reactivity, or corrosion, monitoring.

Environmental Reactivity Monitoring

Reactivity monitoring can characterize the destructive potential of an environment. The growth of various corrosion films on specially prepared copper, silver, and/or gold plated sensors provides an indication of the type(s) and level(s) of essentially all corrosive chemical species present in the local environment. Both passive and real-time reactivity monitors are currently available that can be used to gather important information on gaseous contaminants and their levels in the environment.

Based on joint research performed by Purafil Inc.2,3, the government of the Netherlands4, and the Comitato Termotechnical Italiano (C.T.I.) 5, reactivity monitoring has been accepted as the preferred air monitoring method in preservation environments. It has become the standard for air quality monitoring in government archives in the Netherlands6 and is being proposed as a European standard. These control specifications are shown in TABLE 1 above.

Reactivity monitoring makes it possible to easily identify and quantify those contaminants most dangerous to preservation environments, however, there has been little research done to determine what levels actually cause deterioration of historical artifacts and archival materials. In general, guidelines call for interior concentrations of gaseous contaminants to be maintained as low as attainable by gas-phase air filtration. This can be accomplished through the use of various dry-scrubbing air filtration media7 employing the processes of physical adsorption and/or chemisorptions.

Filtration Systems

The research referenced above not only looked at gaseous contaminants and their effects and evaluated environmental monitoring methods, it also looked at determining the best contaminant control strategies.

In terms of gaseous contaminants, it has been determined that (at least) two different dry-scrubbing media will be required.4 One should be a potassium permanganate-impregnated alumina (PPIA) media for the removal of nitric oxide, ozone, sulfur dioxide, hydrogen sulfide and formaldehyde (among others). The other should be a caustic-impregnated activated carbon/activated alumina (CICA) media for the removal of nitrogen dioxide, organic acids, and nitrogen and sulfur oxides (among others). Both of these media remove gaseous contaminants by adsorption and chemical reaction which irreversibly binds contaminants to the media, preventing their release back into the environment.

It was mentioned above that particulates are one of the main factors which can cause the degradation of archival materials and historical artifacts. This is particularly true where temperature and humidity are not properly controlled. Therefore, particulate filtration must also be part of any contaminant control system for preservation environments.

The optimum filtration system for museums will address as many of the potentially offending materials as possible - gaseous and particulate. The recommended system would consist of (1) a 30 percent ASHRAE-rated prefilter (class EU4); (2) a bed of PPIA media; (3) a bed of caustic-impregnated media; and (4) a 90-95 percent ASHRAE-rated final filter (class EU8/9). Any contaminant control system for these environments that does not meet these minimum requirements should not be considered.

Standing The Test Of Time

The specialized air quality needs of museums and other preservation environments is being acknowledged and acted upon at sites all around the world. This includes both the monitoring and the mitigation aspects of contaminant control. Continuous monitoring of gaseous contaminants has essentially become a requirement in order to provide accurate environmental assessments. The installation of a filtration system for the removal of both gaseous and particulate contaminants is probably even more important. Some examples of this are listed below.

• The filtration system described above as well as reactivity monitoring is required in all government archive buildings in the Netherlands, including the General Government Archives at the Hague.
• The Italian government required the installation gas-phase air filtration and reactivity monitors as part of the restoration and renovation of the Leonardo da Vinci's "Last Supper." Reactivity monitors are also installed in the Sistine Chapel.
• The Shrine of the Book at the Israel museum in Jerusalem is using reactivity monitoring to help protect the Dead Sea Scrolls.
• New national archive facilities in Singapore, Australia, and New Zealand have all made gas-phase air filtration and reactivity monitoring part of their environmental control strategies.
• Gas-phase air filtration is currently in use in the U.S. National Archives, Archives II, and the state archives of Arizona, California, Georgia, Minnesota, Missouri, and Washington. The National Archives, Archives II, and the Minnesota State Archives are using reactivity monitoring as well.

Conservationists and preservationists are expected to provide and maintain environments sufficiently well-controlled as to minimize the decay of artifacts and materials. Thus the total environment, external and internal, must be considered to accurately assess the potential for damage from environmental factors and adequate control measures must be employed for all. Anything less in a control strategy could result in the damage or destruction of materials that can never be replaced or restored.

References

1. Muller, C.O. 1996. "Airborne Contaminant Guidelines for Preservation Environments," Proceedings of the 24th Annual Meeting, American Institute for Conservation of Historic and Artistic Works, Washington, D.C.
2. Muller, C. 1999. "Results of Silver Reactivity Monitoring in Preservation Environments," submitted for publication to the AIC Journal.
3. Muller, C. 1997. "Reactivity Monitoring: A New Tool in Preservation Environments," INvironment Professional.
4. Vosteen, R. and Bakker, R.W. 1992. Delta Plan for Cultural Preservation - Air Purification Pilot Project: Research Methods for Air Purification in the General Government Archives (ARA). Government Building Service, Planning & Techniques Board, Department of Climate Techniques, The Hague, The Netherlands.
5. "Microclima, Qualità Dell'Aria E Impianti Negli Ambienti Museali," Giornata Seminariale, Associazione Italiana Condizionamento dell'Aria Rescaldamento, Refrigerazione, Firenze, Italy, pp 39-66, February 1997.
6. Vosteen, R. 1994. "Advisory Guide-Line Air Quality Archives," Delta Plan for Culture Preservation, Ministry of Housing, Spatial Planning and the Environment, Government Buildings Agency, The Hague, The Netherlands.
7. NAFA, 1993, NAFA Guide to Air Filtration - Chapter 11, Washington, D.C.: National Air Filtration Association.

Chris Muller has been conducting and directing environmental surveys and research in museums, libraries and archives for more than 10 years. He is chair of ASHRAE's SPC 145P, which is developing standards for assessing the performance of media and equipment used in gas-phase air filtration systems. You can reach him by calling (770) 662-8545.