Exploring

External Factors

Pollutants

The outside edges of the pages in this book have darkened because of exposure to pollutants when the book was stored closed on the shelf.

Airborne contaminants in the form of gases and particulates jeopardize the preservation of collections.

For repositories in urban areas, gaseous pollution from sources such as industrial discharge, motor vehicle exhaust, and other combustion products can be a serious concern. Gaseous pollutants can also originate indoors, given off by common substances such as paint, cleaning supplies, untreated wood, photocopiers, and certain kinds of adhesives and plastics. Various types of gaseous pollutants initiate chemical reactions that contribute to the deterioration of paper-based collections. These reactions are usually worsened when high relative humidity is also present.

Particulates come in the form of tiny solids—grit, grime, smoke, dust—which originate largely in industrial processes, vehicle engines, wood-and coal-fired heating systems, smoking, and cooking. They are generally abrasive and acidic and often highly reactive chemically.

Photographs in particular are extremely sensitive to atmospheric pollutants. Particulate pollutants may cause abrasion of emulsions and attract mold or insects. Gaseous pollutants such as sulphur dioxide, nitrogen oxides, ozone, and formaldehyde contribute to sulfiding, redox reactions, and dye discoloration.