The size of combustion generated particles ranges from a few nanometers up to 1 micron, whereas the size of naturally occurring PM such as pollens, plant fragments, and sea salt is generally larger than 1 micron. Particles generated by photochemical processes in the atmosphere are generally smaller than 1 micron. Ultrafine particles (UFP), also called “nanoparticles”, are <0.1 micron and in recent yearshave attracted attention due to potential adverse health effects associated with them. The contribution of UFP to the total PM mass is very small. However, they dominate the total number of particles in urban aerosols. Their sources are both mobile and stationary combustion sources and also gas-to-particle conversions. In coal and waste combustion systems, UFP are hypothesized to be generated mainly by nucleation of metal vapors. Coal naturally contains a vast range of inorganic elements among which are heavy metals. Sources of heavy metals in MSW include batteries, electronic devices, light bulbs, house dust and paint chips, food containers, used motor oils, plastics, yard wastes and some papers. The input of these metals into WTE facilities can be controlled by better source-separation of metal-containing materials. In 2007 almost 50% of the approximately 4.16 billion MWh generated in the United States was produced by coal power plants whereas only 0.3% was generated by the WTE industry. A preliminary study has shown that in terms of contribution to UHF in the atmosphere, MSW combustion has a minor effect in comparison to coal-fired power plants in the U.S. This paper will report on the results of this investigation.

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