The evaluation of the air quality is an important aspect within the preventive conservation of our heritage. The monitoring of relevant environmental parameters such as relative humidity, temperature, light and pollutants, however, entails large amounts of measuring data. To support the heritage guardian in interpreting and evaluating these data, we developed an indoor air quality index that summarizes the data. The index is time dependent and material specific. With an intuitive visualization of the index in a color bar, the environmental risk for the collection directly becomes visible. In this way, periods with elevated risk of damage can easily be detected, and their cause can be determined. Be aware that the index is developed for indoor applications.