Coarse particulate matter (PM 10 - 2.5 ) concentration data from residential outdoor sites were collected using portable samplers as part of an exposure assessment for the North Carolina Asthma and Children's Environment Studies (NC-ACES). PM 10 - 2.5 values were estimated using the differential between independent PM 10 and PM 2.5 collocated MiniVol measurements. Repeated daily 24-h integrated PM 10 and PM 2.5 residential outdoor monitoring was performed at a total of 26 homes during September 2003–June 2004 in the Research Triangle Park, NC area. This effort resulted in the collection of 73 total daily measurements. This assessment was conducted to provide data needed to investigate the association of exposures to coarse particle PM mass concentrations with observed human health effects. Potential instrument bias between the differential MiniVol methodology and a dichotomous sampler were investigated. Results indicated that minimal bias of PM 10 - 2.5 mass concentration estimates (slope = 0.8, intercept = 0.36 μ gm - 3 ) existed between the dichotomous and differential MiniVol procedures. Residential outdoor PM 10 - 2.5 mass concentrations were observed to be highly variable across measurement days and ranged from 1.1 to 12.6 μ gm - 3 (mean of 5.4 μ gm - 3 ) . An average correlation coefficient of r = 0.75 existed between residential outdoor PM 10 - 2.5 mass concentrations and those obtained from the central ambient monitoring site. Temporal and spatial variability of PM 10 - 2.5 mass concentrations during the study were observed and are described in this report.