The chemical speciation and source attribution analysis of fine particulate samples (PM2.5) collected at San Augustine, TX, and Dallas, TX, are presented. The total ratio of measured saccharides to organic carbon (OC) in PM2.5 was higher at San Augustine than Dallas, suggesting that biologically related sources, which are enriched in these compounds are a greater contributor to the fine aerosol OC loading in the rural location. Mean concentrations of n-alkanes ranged from 0.01 to 38.1 ng/cu m for San Augustine and 0.16 to 30.7 ng/cu m for Dallas. n-Alkanes measured in ambient PM2.5 samples collected in San Augustine exhibited odd carbon number of predominance, as expected for a predominantly rural site with little input from petroleum-derived fuels. However, for samples collected at Dallas, little or no odd carbon number predominance was observed, which was characteristic of the strong influence of emissions derived from fossil carbon sources. EPA's Positive Matrix Factorization (PMF) model was used for modeling both urban both urban and rural ambient concentrations. Ambient market concentrations for 25 and 37 sampling days for Dallas and San Augustine, respectively, were used in this analysis. Similar profiles were resolved using PMF for both the datasets. This is an abstract of a paper presented at the 103rd AWMA Annual Conference and Exhibition (Calgary, Alberta, Canada 6/22-25/2010).