Our results highlight the importance of both infiltration of outdoor pollutant concentration and indoor sources, especially smoking, on indoor exposures in industrial communities. We hypothesized that outdoor concentration would be strong predictors our indoor models. For both the summer and winter indoor BC models and the winter 〖PM〗_2.5model, outdoor estimates modified by the I/O sulfur ratios explained at least 33% of the variability found in indoor concentration. We hypothesized smoking to be the most predictive indoor pollution source, Which was corroborated in both summer 〖PM〗_2.5and BC models, as well as the winter 〖PM〗_2.5model. Outdoor infiltration explained moderate variability in indoor 〖PM〗_2.5and BC concentration, yet smoking contributed to higher concentration increases. In both seasons, indoor concentrations for both 〖PM〗_2.5and BC were consistently higher than residence-specific outdoor concentration estimates.