Long-term preservation of the Libraries' collections includes managing the environment in buildings that store collections. A properly managed environment can slow deterioration and decay resulting from incorrect temperature and relative humidity, and overexposure to light and pollutants.

Books and paper are susceptible to damage from temperatures that are too high, and relative humidity that is either too high or too low. The Libraries conduct systematic monitoring with electronic dataloggers in specific areas of the building. These devices continuously measure and record temperature and relative humidity, so conditions are documented and are tracked over time.

The following recommended standards are for paper-based (archival, textural, library materials, prints, drawings) collections:

• Temperature – range from 65° to 70°F (+/- 2°F)
• Relative Humidity (RH) – range from 30% to 50% (+/- 5%)
• Optimum preservation environment: 35° to 65°F, 30% to 50% RH
• Lack of fluctuation within a range and long-term averages are more important than exact temperature or RH
• The warmer it is and the higher the moisture content, the faster the deterioration of materials

The display on the datalogger shows the temperature (73.26° F) and relative humidity (43.8%).

All light is damaging to paper materials, and leads to embrittlement, yellowing, and/or fading--all of which are irreversible. Light level and UV readings guide decisions on lighting in exhibit areas and UV protection for collections storage.

An example of sunlight damage to a book spine:

Equipment used to measure light and UV levels:

Controlling the air quality reduces as many pollutants in the building as possible. Clean air prevents chemical reactions that lead to acid formation in items, and keeps dirt and particulates from abrading or soiling items. The Libraries work with Facilities Management to monitor air quality.