What effect does exposure to indoor air pollutants have on a museum’s collections?
Accelerates aging and deterioriation
Indoor air pollution is a complex area of study. Pollutants work in combination with other factors, such as temperature, relative humidity (RH) and light to cause deterioration. The museum environment poses a particular challenge because objects are often exhibited or stored in microenvironments, such as display cases or storage units. If the enclosure were made of a pollution emitting material, it would create a microenvironment in which the pollutants would remain confined with the objects. There are many measures that the Museum takes to eliminate this hazard. This section will define indoor air pollutants found within a museum environment, identify the likely origins of the pollutant and illustrate what a museum may do to reduce the presence of a pollutant.
The main sources of indoor air pollutants come from building materials or from museum objects themselves and may include the following:
The chart below is adapted from the National Park Service Museum Handbook, 1999 (sulfur oxides and nitrogen oxides are outdoor air pollutants primarily from products and combustion of fossil fuels)
|Object Materials||Deterioration||Primary air pollutants||Factors accelerating damage|
|Metals||corrosion/tarnishing||sulfur oxides, hydrogen sulfide, and other acidic gases||water, oxygen, salts|
|Stone||surface erosion, discoloration||sulfur oxides and other acidic gases, particulates||water, temp fluctuations, salts, vibration, microorganisms, carbon dioxide|
|Paint||surface erosion, discoloration||sulfur oxides, hydrogen sulfide, ozone, particulates||water, sunlight, microorganisms|
|Textile dyes and pigments||fading, color change||nitrogen oxides, ozone||sunlight, water|
|Textiles||weakened fibers, abrasion, soiling||sulfur oxides, nitrogen oxides, particulates (dust)||water, sunlight, mechanical wear|
|Paper||embrittlement||sulfur oxides||moisture, mechanical wear|
|Leather||weakening, powdered surface||sulfur oxides||mechanical wear|
|Ceramics||damaged surface||acid gases||moisture|
How can pollutants in a museum environment be detected?Reactivity of metal samples in an enclosed chamber: This test is routinely carried out in the Museum to determine if pollutants from wood, fabric, labels, glues and tapes are present within an enclosed space (for example an exhibit case) that will cause damage to metal.
Passive sampling devices or bioindicators: Devices that absorb particular pollutants are placed in an area of concern for a period of time. Then the device is analyzed for the presence and levels of pollutants. Each passive sampling device will measure one type of pollutant.
A-D strips: These strips detect acetic acid and were developed for film collections. When acetate film deteriorates it emits acetic acid or “vinegar syndrome.” The strips change color as the level of acidity increases.
What is done to reduce or control pollutants in the museum environment?As with temperature and humidity controls, the Museum’s HVAC (climate control) system plays a tremendous role in the reduction of dust, particulate and gaseous pollutants. Many damaging pollutants are handled through the use of a layered filtration system (air filters and activated charcoal filters) within the air handling systems at the Museum.
In exhibit cases and storage units, care is taken to select materials that will not emit harmful pollutants.Other considerations for controlling pollutants in a musem environment:
- Good housekeeping practices in storage areas to ensure a dust free environment
- use HEPA filters in vacuum cleaners to limit particulate re-distribution
- Separate office areas from museum collections areas
- less traffic around collections means a cleaner area
- Maintain seals and weatherstripping around doors and windows
- Appropriate museum storage and exhibit units
- choose safe materials and maintain sound gaskets
- Store archival materials in acid-free boxes or folders
- Chemically free dust covers for objects exposed to air and open shelving
- clear polyethylene sheeting, unbleached cotton muslin, Tyvek® or Gore-Tex®
- Separate out objects that might emit pollutants
- for example, cellulose nitrate film negatives or objects containing hardwoods such as oak, birch or beechwood
- Cold storage to slow deterioration
- Avoid using exhibit materials that off-gas organic acids or seal them prior to use
- for example, adhesives used in some plywood, particle board or veneers
- Natural fiber fabrics, such as linen and cotton, are often good choices for exhibit case linings
- Some brands of MDF (medium density fiberboard) used for case and exhibit construction are selected because they contain no added formaldehyde that would harm artifacts in an enclosed environment
- Vapor barriers, such as paint and Marvelseal™, are used in exhibit and display case construction as a barrier against off-gassing of chemical pollutants
- Filters, such as activated carbon paper, and pollutant scavengers, such as Corrossion Intercept®, are also effective measures