Size-segregated aerosol samples were collected with Micro-Orifice Impactors in Baltimore, MD, a typical northeastern port city where air quality is influenced by urban and industrial sources. The size fractions were analyzed for up to 32 elements by Instrumental Neutron Activation Analysis and the results were used in a chemical mass balance model to resolve the contributions to ambient levels by size and by source. Resolution by size improves interpretation of the results as primary accumulation aerosol populations from different sources are frequently resolved in the size spectra of their marker species. With a 15-source model, agreement between measured and predicted concentrations was within 40% for all elements except Co, Cr, Cs, Ti, and W. The results suggest that coal-fired power plants are minor sources of the respirable fractions of several metals, including Cr (19%), V (5%), and Zn (<1%), which are known to be active in cytokine assays, a metric of inflammatory response that is linked to reactive oxygen species production and lung cell necrosis in in vitro and animal studies. Coal combustion contributions to ambient levels of As, Fe, Co, Mn, and Sb were 16, 13, 11, 2.7, and 4.8%, respectively. In addition, coal contributions are likely 30% less than these after correction of the source signature for vapor-phase Se emissions. Major fractions of respirable airborne V and Co (each about 55%), and Zn (70%) were attributed to aerosol emitted from fuel oil combustion and incinerators, respectively. Steel production was the major source for airborne Cr (45%), Fe (52%), and Mn (52%); whereas large (70 and 57%) fractions of airborne As and Sb were attributed to an unidentified source which was resolved in the size spectra. Metal concentrations attributed to long-range transport, owing to their association with secondary sulfate were typically negligible, except for Mn (15%), Se (28%), and Zn (5%).