Gaseous pollutants

Generally, gaseous pollution is caused by the burning of fuels. Pollutants such as sulphur dioxide, hydrogen sulphide, and nitrogen dioxide combine with moisture in the air to form acids that attack and damage library material. Ozone is a powerful oxidant which severely damages all organic materials. It is a product of the combination of sunlight and nitrogen dioxide from car exhaust; it may also be produced by electrostatic filtering systems used in some air conditioners, as well as by electrostatic photocopy machines.

Smoking, cooking, and off-gassing from unstable materials (cellulose nitrate film, paint finishes, fire-retardant coatings, and adhesives) may also produce harmful gaseous pollutants. Wood, particularly oak, birch and beech, emit acetic and other acids, and vulcanized rubber releases volatile sulphides that are especially damaging to photographs.

The composition of all equipment, materials, and finishes used for the storage, transport, and display of objects should be tested by recognised methods to ascertain whether they are likely to produce harmful emissions.