Low winter temperatures will cause moisture to condense on the windows of a room having relative humidity of 45 to 55 percent. There is evidence that regular changes in temperature and relative humidity can lead to weakening of paper, as a result of internal stresses set up in the paper as it responds to these changes. These ranges should be adequate to protect and prolong the life of general library materials including printed books and journals, microforms, and audiovisual collections. Fresh air exchange should not only comply with all code requirements, but also accommodate staff and students spending hours sitting at computers or at tables. Mold Mold or mildew attacks on books can occur when both temperature and humidity are uncontrolled.
Mold spores are always present in the air and on books.
Mold prevention requires that both temperature and humidity be kept within the ranges suggested above. Atmospheric Pollutants Such gases as sulfur dioxide, hydrogen sulfide, and nitrogen dioxide are often major factors in the deterioration of paper. They originate from the burning of fossil fuels or other combustion or chemical processes such as occur in furnaces, automobiles, power plants, and the like, and are, therefore, most serious in urban areas. Ozone, another atmospheric pollutant, also causes the oxidation and consequent embrittlement of paper. A prominent constituent of smog, ozone is also produced by electrostatic filtering systems, sometimes used ignorantly by architects and engineers in the air conditioning of libraries and archives.