The composition and concentration of submicron particulate matter (PM1) were measured by an Aerodyne high-resolution time-of-flight aerosol mass spectrometer at three locations: Dallas-Fort Worth (DFW), TX (June, 2011) Centreville, Al (June 1st –July 15th , 2013) and Houston, TX (May 12th -29th , 2015) to improve the understanding of the sources and transformation processes of PM1 components with an emphasis on Organic aerosol (OA) and relationships between secondary OA concentrations and various aging metrics in these three US cities. OA and sulfate aerosol were the most dominant PM1 components in all three sites. The DFW site was the cleanest with respect to PM pollution. The lowest concentrations of OA, sulfate, and total PM1 were observed at this site. Centreville, the most rural site, was characterized with the highest average concentrations of OA and total PM1. This indicates significant transport of material from urban locations and the influence of local biogenic VOC emissions. Houston site was characterized with frequent high peak events of organics and sulfate resulting from point source emissions. High OA events were mostly driven by emissions from Houston Ship Channel. OA in both DFW and Houston was apportioned into three OA factors including hydrocarbon-like OA, semi-volatile oxygenated organic aerosol (OOA) and low-volatility OOA. OA in Centreville was apportioned into four factors including isoprene-derived OA (IEPOX OA), biomass burning organic aerosol (BBOA), SVOOA, and LVOOA. This study uses a variety of aging metrics and their relations to OA/ΔCO and OA/ΔCO factor to characterize SOA. In DFW, LVOOA/ΔCO shows a positive correlation with sulfate aging metric and SVOOA/ΔCO shows an overall increase with nitrogen aging metric, indicating the different origin of the two OA factors, regional and local, respectively. In Centreville, a significant positive correlation is observed between LVOOA/ΔCO and the nitrogen aging metrics, which signifies the local characteristic of LVOOA at this site.