This paper describes the ongoing development of a software tool to help museums, galleries, archives and libraries deal with air pollution damage to collections caused by pollutants from the external environment, such as sulphur dioxide, nitrogen dioxide and ozone. The tool provides information, advice and case studies on pollution damage, and has at its core a computer model to predict the performance of buildings in controlling external pollutants. It will estimate concentration ratios of indoor to outdoor pollution from a range of building parameters, such as ventilation strategy and rate, interior layout and surface finishes. The software tool is being developed in close cooperation with museum partners and other potential users, such as architects and engineers. On completion, the software tool will be available through a freely accessible Web site.