A selection of shrubs from California and Arizona and forest fuels from North Carolina and Georgia were burned under controlled environmental conditions at the USDA Forest Service's Fire Science Laboratory in Missoula. The goal was to improve measurement of particle emission factors. The chemical and physical properties of PM2.5 emissions during flaming and smoldering phases were characterized using a suite of real-time and off-line instrumentations. The particle size distribution indicated the number distribution peaked around 50nm for flaming and evolved into bimodal distribution with a second peak below 10nm during smoldering phase. EC/OC analysis of quartz filters suggests OC contributes to the most of total carbon fraction. A High Resolution Time-of-Flight Aerosol Mass Spectrometer identified the organic biomass signature in particles associated with the flaming and smoldering phases while ammonium nitrate, sulfate and chloride species were only observed during flaming stage. Elemental compositional analysis of oxygen and carbon indicated little changes in the O:C ratio (∼0.25-0.30) throughout entire burn. PM samples also were taken using a NIOSH-developed portable electrostatic precipitator. TEM, EDS, and Image analysis were used to classify recognizable morphologies ad to perform elemental analysis on PM.