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Sources of carbonaceous PM2.5 were quantified in downtown Cleveland, OH and Chippewa Lake, OH located similar to 40 miles southwest of Cleveland during the Cleveland Multiple Air Pollutant Study (CMAPS). PM2.5 filter samples were collected daily during July-August 2009 and February 2010 to establish the seasonal emission patterns from local and regional sources. Radiocarbon (C-14), redox species (NOx, SO2 and ozone), 28 primary and secondary organic aerosol tracers, elemental carbon (EC) and organic carbon (OC) measurements were analyzed using the EPA Positive Matrix Factorization (PMF) model to apportion carbonaceous aerosol sources. Five sources were identified at each site: mobile sources, fossil fuel combustion from fuels containing sulfur, local biomass combustion, other combustion (regional biomass, waste, meat, coal), and secondary organic aerosol (SOA). C-14 data were incorporated in the PMF analysis as a novel method to obtain the modern carbon fraction (f(mod)) of each source individually which aided all factor interpretations. SOA was the principal carbon source during summer as shown by the PMF analysis and a separate tracer based mass fraction method while biomass burning and other combustion sources were dominant in winter. Elevated levels of EC and fossilized carbon in downtown Cleveland are primarily attributed to increased mobile source and coal combustion emissions. Published by Elsevier Ltd.