Research at the U.S. Environmental Protection Agency's (EPA's) National Risk Management Research Laboratory (NRMRL) in the area of particulate matter (PM) is designed to provide critical information regarding emission rates, characteristics, and control approaches in aerodynamic diameter. This research will provide information needed by source receptor models to identify the contribution of different sources to the ambient particle loading. Emissions characterization research is being conducted on particle size and composition for residual wood combustion systems such as woodstoves and fireplaces, for industrial combustion sources burning coal and heavy fuel oil, for diesel truck engine during on-road operation, and for open burning of biomass. Researchers are studying innovative control technologies for stationary sources, and they are also collaborating with different scientists and organizations to link particle characteristics to health effects and particles in the atmosphere to create a base of broad scientific expertise and interaction.