The paper discusses an indoor air quality (IAQ) model for particulate matter (PM). The standard for PM<2.5 micrometers in aerodynamic diameter (PM 2.5) proposed by the U.S. EPA has produced considerable interest in indoor exposures to PM. IAQ models provide a useful tool for analyzing both the indoor exposure to PM and the impact of risk management options on exposure. Because analysis of the impact of PM exposures requires analysis over a particle size distribution most existing IAQ models, which are designed to allow analysis of the impact of a single pollutant component, are not well suited for analysis of PM exposure. TO overcome this limitation, a multicompartment IAQ model for PM exposures for a full particle size distribution was developed. The model allows analysis of the effect of: the building shell on the penetration of outdoor particles into the indoors, the deposition of particles to indoor surfaces, particle removal by air cleaners, and indoor particle sources. The use of the model is demonstrated by an analysis of both the time-varying impact of outdoor PM on indoor PM levels and the effect of a central furnace filter on indoor PM concentrations.