Relative humidity refers to the amount of moisture in air. Organic materials absorb or give off moisture in a continuous attempt to achieve equilibrium with the atmosphere. Inorganic materials usually are not affected by relative humidity levels unless they contain salts or are otherwise unstable. Metals, however, are best preserved at low relative humidity. Serious damage can occur when materials are subjected to dramatic, sudden changes in relative humidity over short periods.
Temperature is significant because it affects relative humidity.
Temperature is also important because deterioration progresses much more quickly at higher temperatures than at lower ones. Exposure to heat can drastically accelerate the aging of organic materials and of many modern synthetics. Air pollution can be generated inside buildings as well as outside. Its components include acidic gases, particulate material, and ozone. Many of the chemicals known to cause human health problems can also harm objects.