An indicator system provides a visual indication of the cumulative level of an airborne contaminant. An indicator has a transparent sheath with support medium treated with acid and a pH indicator, as the contaminant is adsorbed, the color changes along the medium. The indicator system may be used with an adsorptive filter system to predict the life of adsorption bed assemblies. A sample flow is taken upstream of the adsorption beds and is calibrated with a flow meter and valve. By monitoring the indicator, an accurate prediction of adsorption bed life may be made.