Home- and week-specific outdoor concentration estimates were derived using our previously-published full-week LUR models for PM2.5 and BC (Tunno et al., 2015). This outdoor sampling campaign was systematically designed to sample across 37 areas with contrasting gradients of traffic density, elevation, and industrial emissions (Shmool et al., 2014), in an attempt to seek out the effect of industry, terrain, and traffic congestion on outdoor PM2.5 and BC. In these outdoor models, industrial emissions, traffic density, and elevation explained substantial spatial variance across our domain, after accounting for temporal variability using an upwind reference site (Tunno et al., 2015). For the present study, we calculated outdoor concentrations at each home using the mean value from the LUR surface for the area within 300 m of each home, as in Ross et al. (2013), and hourly EPA Air Quality System (AQS) data for PM2.5 from the nearby Liberty and Lawrenceville monitoring locations (Fig. 1), averaged for the specific sampling hours at each home. These LUR-based outdoor estimates (Tunno et al., 2015) were also used to calculate indoor/outdoor ratios for PM2.5 and BC at each home.