Air pollutants have long been known to damage materials stored indoors. Harmful pollutants include those admitted from outdoors along with those produced inside rooms, display cases and storage cabinets. Some air pollutants, particularly gases that are acids (e.g sulfur dioxide, nitric acid, formic acid), oxidizing agents (ozone, hydrogen peroxide) and reducing agents (hydrogen sulfide, carbonyl sulfide) and suspended particulate material (soot, fibres) can harm collections. The forms of damage and way air pollution induces these changes are important in developing control strategies. A range of methods are available to determine the concentration of air pollutants indoors, but the choice depends on the types of damage and pollution present. It is possible to reduce the air pollution concentrations in a building by filtering the air or absorbing harmful gases, but this may be beyond the resources of many museums. However, simpler and less expensive approaches might involve removing harmful pollutant from a cabinet or other enclosure along with the appropriate choice of construction and display materials used in the rooms, cases and cabinets.