ABSTRACT Decreasing building energy demands will necessitate changes in HVAC design and operation. Such changes may have a wide spectrum of effects on indoor air quality. Human exposure to a wide range of air pollutants@ particularly toxic contaminants@ is dominated by what is breathed indoors. Two contaminants@ p-dichlorobenzene (p-DCB) and naphthalene are both classified as Group C carcinogens according to the US EPA@ and these chemicals exist in nearly pure form in consumer products within which they are used. Products that contain p-DCB include moth crystals@ closet air fresheners@ and toilet bowl deodorizers. Moth balls@ which serve as a moth repellent@ are the main products that contain naphthalene. Emission rates of p-DCB and naphthalene from these products have been ascertained from a previous study and range from 50 mg/hr to 300 mg/hr for p-DCB products and 5 mg/hr to 12 mg/hr for naphthalene products. Emission rates were employed in a well-mixed reactor model to estimate indoor concentrations and the extent of dynamic sorptive interactions between these chemicals and two indoor materials: gypsum wallboard and carpet. In particular@ we explore the effects of HVAC operation on sorptive interactions between these pollutants and the two indoor materials. HVAC cycling enhances the adsorption and desorption mechanisms that occur when indoor pollutants are present.