Filter samples have been collected and analyzed for chemical composition at a number of sites in New York state for more than 2 years. Because of the broad focus of the New York Environmental Protection Agency Supersite program, these sites include remote, rural, and urban sites in midsized and large cities. Calculated blanks and laboratory reported minimum detection limits (MDLs) for all measured species are presented. Data are averaged by location and season and presented for six sites throughout New York state. Data are presented for PM2.5 mass, sulfate, nitrate, ammonium and carbon, and selected metals and groups of trace elements. An approximate ion balance of the major inorganic ionic species is also calculated, which shows a predominately negative ion balance with the rural and remote sites being the most negative. In addition to chemical composition values in mass per unit volume (reported to ambient conditions), we also calculate ratios of the mass concentration values for five sites referenced to our site that is closest to background, Whiteface Mountain in the Adirondacks. By computing base ratios for the various chemical components and ratios of ratios referenced to mass concentrations, we can provide some insight into the sources of these chemical components relative to the sources of PM2.5 mass. The ratio of ratios analysis indicated that sulfate and potassium are the most regional species considered and that EC and some metal species have the strongest urban (especially New York City) sources.