A methane-air flat flame reactor was designed to study the initial stages of combustion through flash pyrolysis of biomass and factors contributing to particulate emissions were examined. Six different types of biomass, Prosopis juliflora, cotton stalk, poplar, applewood, oak, and cherry wood were pyrolysed in a methane-air flat flame at various moisture contents. Particulate matter formed was characterized through measuring mass, and particle number size distributions. The moisture content of biomass feed stock was varied from 0% to 20%, while the particle feed sizes were maintained at 105 mu m or below, to limit heat transfer effects in the particle. Thermo-gravimetric analysis was also conducted on the biomass to obtain mass fraction data (% volatiles, moisture content) along with kinetic data. Results indicated that the presence of moisture causes a delay in devolatilization thus decreasing the overall efficiency in combustion. The results from this study can be used to optimize biomass combustion for use as fuel in household settings to minimize negative impacts due to poor air quality. (C) 2013 Elsevier Ltd. All rights reserved.