Particulate matter (PM) emitted from biomass burning and wildfire has been an air quality concern in affected areas such as dense population centers. Because of regulatory requirements, airborne particles smaller than 2.5 µm (PM2.5) are of special concern. Controversy has arisen about the soutce of PM2.5, with smoke from prescribed fire and other biomass burning being a convenient target for elimination by regulators as a means to improve air quality. Because PM2.5 may come from several sounces a rapid yet sensitive method is needed to trace PM2.5 emitted during biomass burning and to determine if discrimination between sources is feasible. We initiated this research to identify the chemical signature of PM2.5 emitted during biomass burning with a rapid multi-element scanning thermal analysis (MESTA) method and to test the hypothesis that this chemical signature can be used to trace its presence in the air. We collected PM2.5 samples from the ambient air and experimental burning of pine (Pinus spp.) forest biomass and analyzed them with the MESTA method. The MESTA thermograms show that the PM2.5 emitted from the prescribed burning of biomass has a characteristic high-temperature-volatile (>300ºC) component with very low nitrogen (N) and sulfur (S) contents, whereas PM2.5 in the ambient air has a characteristic low-temperature-volatile (>300ºC) component with very high N and S contents. The sharply contrasting MESTA chemical signatures between the experimental biomass burning PM2.5 and the ambient air PM2.5 provide a promising means to trace and quantify the presence in the air of PM2.5 resulting from biomass burning. © 2010, Tall Timbers Research, Inc.