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Environmental Control
Temperature and Relative Humidity | Guidelines for Temperature and RH | Pollutants | Guidelines for Pollutant Levels | Light | Guidelines for Light Levels
Pollutants
Like temperature and humidity, the damaging effect of pollutants on collections can be difficult to see in the short-term, but very serious over the long term. Pollutants fall into two general categories (particulates and gases) and may originate outdoors or within the building.
Particulate Pollutants
Deposits of particulates around this ceiling air vent indicate that particulate filtration is inadequate.
Particulates consist of organic and inorganic materials (e.g., hair, skin cells, soot, fibers, pollen, metals, salts, plaster, etc.) that may come from humans, smoke, cooking, construction materials, heating systems, and other sources. Particulates are categorized by size; fine particles have a diameter of 2.5 microns or less, while coarse particles have a diameter of 2.5-10 microns. Particulates are abrasive, they attract insects, and many are acidic, reacting with moisture to worsen chemical deterioration. The effect of particulate pollutants worsens in the presence of high relative humidity and temperature.
Gaseous Pollutants
Common gaseous pollutants in the outdoor environment include sulphur dioxide (which comes from combustion of fossil fuels), nitrogen oxides (mainly from traffic exhaust), and ozone (produced by heavy electrical machinery, as well as when light reacts with nitrogen oxides). Indoor pollutants can unfortunately also be a problem. Ozone is produced by photocopiers, laser printers, and electrostatic air cleaners. Acids, ammonia, formaldehyde, and peroxides are also produced by indoor materials such as cleaning products, particleboard, adhesives, and oil paints.
The amount of outdoor pollution that actually penetrates a building and affects collections is difficult to quantify, but certainly evidence has shown that collections in urban institutions are more acidic than those in institutions located in more rural settings. Gaseous pollutants can be unpredictable; even in fairly small concentrations they may interact with each other to cause damage.
Take a few moments to reflect on the scenario below. Why do you think this problem occurred? Click on Show Answer to see.
: The Mountainside Public Library
Pollutant damage is cumulative and irreversible, and follows the rule of reciprocity. Thus, exposure to a high level of pollutants for a short time is equivalent to exposure to a lower level for a long period of time.
