Investigation of Particulate Matter Size, Concentration and Mass Emissions from Small Handheld 2-Stroke Spark Ignition Engines Yashwanth Chowdary Maddineni Quality of air, change in the climate and exposure of humans to pollutants have become major concerns globally over the past decade. Particulate matter has been linked to many adverse health effects. Internal combustion engines are major source of PM emissions. Knowing the adverse health effects of particulate matter, the regulatory agencies are in the process of introducing strict regulations to limit the quantity of PM emitted by off-road small handheld gasoline engines. Two-stroke small engines typically emit more smoke as they burn oil-gasoline mixture compared to four-stroke engines running on gasoline only. Current regulations in the United States for these engines regulate only HC+NOx and CO emissions. In spite of their contribution to atmospheric pollution and negative health effects, the PM emissions from handheld, two-stroke engines are yet to be regulated. This led to this study of particulate matter emissions from these engines. The main objective of this study was to measure particulate matter size, concentration and mass distributions from 2-stroke handheld 25cc weed whacker engine and to evaluate the effect of heat treatment on these emissions in removal of volatile fractions. The exhaust sample was heat treated to different temperatures (200 °C, 150 °C, and 100 °C) before measuring the distributions to better understand what fraction of particulate matter is solid or volatile. Tests were performed in Center for Alternate Fuels, Engines and Emissions Laboratory (CAFEE) at West Virginia University. A Scanning Mobility Particle Sizer (SMPS) Model was used for measuring the particle size distribution and concentrations. The engine was operated at two steady-state modes (wide open throttle) WOT and Idle mode. The WOT mode resulted in a count median diameter (CMD) of 14.1nm when heat treated the sample to 200 ºC compared to 32.1nm for sample in CVS whereas the idle mode resulted in CMD of 5.94nm and 31.1nm respectively. This indicated the existence of volatile particles. These Nano-particles are proved to be harmful to health. Results obtained from the data for the sample in CVS and compared to the data for the heat treated samples, show that the influence of volatile fraction on PM size distribution is reduced with increase in sample conditioning temperatures. The density function used for mass distribution calculations by SMPS does not take diameter of the particle into consideration and so these calculations were compared with the mass distribution calculated by using IPSD method or effective particle density method since previous studies indicated that at ultra-low emission levels this method proved to give more precise results. This comparison resulted in a good correlation in the particle mass distribution given by SMPS.