Pollutants and Collections

Introduction 

If you are familiar with the 10 Agents of Deterioration, you know that pollutants can cause damage to collections. In this context, pollutants are the chemicals that deteriorate or accelerate deterioration of collection objects. Pollutants can be generated outside and migrate into collections spaces (nitrogen oxide compounds from vehicle exhaust), but they can also be generated inside collections spaces (aldehydes generated by wood furniture). In some cases, collections, themselves can be the source of a pollutant that damages objects around them (nitric acid produced by cellulose nitrate based film). Damage caused by pollutants can include physical soiling in addition to chemical changes like the tarnishing of metals, the fading of dyes, the weakening of cellulose, or the formation of crystalline compounds or droplets on the surface of objects.  

Collection pollutants may differ from pollutants in a human health and safety context. For some collections, sodium chloride, oxygen, and water are pollutants. Common collection pollutants, their sources, and affected materials are summarized in Table 1. 

Table 1: Summary of common collection pollutants adapted from Tétreault 2021  

The risk of pollutant damage increases in microenvironments (like sealed cases) because pollutants cannot escape, elevating their concentrations. This can be damaging to human health and safety in the case of pollutant-producing collections. For example, ventilated storage is recommended for collections made of malignant plastics such as cellulose nitrate.  

Monitoring 

There is currently no pollutant equivalent to a temperature/relative humidity datalogger that can be read in house within the budgets of many collecting institutions. A relative humidity monitor actually is a pollutant monitoring device, but it only monitors for a single pollutant: water vapor. Because there are so many different pollutants and there are so many different components of air, it is, at this stage, impossible to have one monitoring device that can accurately measure all the pollutants collections stewards are worried about. Institutions must “pick their battles.” Are you most concerned about a specific collection? Are you worried about the potential that a new material has for off-gassing? Do you have the resources to pursue implementing a monitoring system that is expensive and extensive? 

There are a wide range of pollutant monitoring techniques that vary in their accessibility, specificity, and ability to produce quantitative results. Some examples are presented in Table 2. 

Table 2: Sample of pollutant monitoring techniques 

Techniques of varying costs and detection limits are outlined in the 2006 book by Cecily Grzywacz, Monitoring for Gaseous Pollutants in Museum Environments, and Jean Tétreault’s 2021 technical leaflet, “Control of Pollutants in Museums and Archives – Technical Bulletin 37”.  

While it is preferable that pollutants be intercepted before damage occurs, monitoring sensitive collections can also be informative. Deterioration of these sensitive materials can be an indicator that a specific pollutant is present. Table 3 lists examples of sensitive materials and the pollutants that commonly affect them.  

Table 3: Examples of hypersensitive materials and corresponding pollutants. Adapted from Tétreault 2003, 2021 

Particulates can be monitored directly because they are visible. Simple dust collectors made with tape and label stock or paper can provide a baseline for dust accumulation that informs housekeeping policies and allows later comparison following mitigation activities. 

Mitigation 

Mitigation depends on the pollutant and the form it takes, but a general rule of thumb for pollutant mitigation is to avoid, block, dilute, filter, or sorb pollutants in that order. Figure 1 shows examples of mitigation strategies that fall within those five categories. 

Some collection materials also adsorb and desorb pollutants. This increases the importance of keeping temperature and relative humidity stable to minimize spikes in pollutant levels. 

If you have further questions or concerns about potential monitoring and mitigation options for pollutants in your institution, consult a professional conservator. The “Find a Professional” database of the American Institute for Conservation can help you identify a professional who has expertise with the type of collections under review. https://community.culturalheritage.org/expertsearch 

Additional Resources 

Brimblecombe, Peter. “Air Quality, Monitoring, and Management,” in Elkin, Lisa and Christopher Norris, eds. Preventive Conservation: Collection Storage. New York: Society for the Preservation of Natural History Collections, 2019.  

Gryzwacz, Cecily M. Monitoring for Gaseous Pollutants in Museum Environments. Los Angeles: Getty Publications, 2006.   https://www.getty.edu/conservation/publications_resources/pdf_publications/monitoring_gaseous.html . 

Hatchfield, Pamela. Pollutants in the Museum Environment. London: Archetype Publications, 2002. 

Hatchfield, Pamela. “Pollutants in the Museum Environement: Practical Strategies for Problem Solving in Design, Exhibition, and Storage.” WAAC Newsletter, vol. 26, no. 2, May 2004, pp. 10–22. https://cool.culturalheritage.org/waac/wn/wn26/wn26-2/wn26-204.pdf 

Tetreault, Jean. Airborne Pollutants in Museums, Galleries, and Archives. Ottawa: Canadian Conservation Institute, 2003. 

Tétreault, Jean. Control of Pollutants in Museums and Archives: Technical Bulletin 37. CCI Technical Bulletin, Canadian Conservation Institute, 2021. https://www.canada.ca/en/conservation-institute/services/conservation-preservation-publications/technical-bulletins/pollutants-museums-archives.html#a13. 

Weintraub, Steven. “Specialized Macroclimates and Microclimates: Options for the Control of Temperature, Relative Humidity, and Pollutants,” in Elkin, Lisa and Christopher Norris, eds. Preventive Conservation: Collection Storage. New York: Society for the Preservation of Natural History Collections, 2019.  

Williams, R. Scott. “Care of Plastics: Malignant Plastics.” WAAC Newsletter 24(1), 2002. https://cool.culturalheritage.org/waac/wn/wn24/wn24-1/wn24-102.html 

Updated July 2022.