In recent years since enactment of the NSPS, carbon injection has significantly reduced mercury emissions from MSW units. What is not well known is that carbon injection has also resulted in further unintentional reductions in PCDDs/PCDFs emissions from MSW emissions. These emissions reductions have taken place on a mass basis as well as a TEF weighted basis. The latter have been more pronounced on a percent reduction basis owing to changes in the PCDDs/PCDFs profile directly attributable to preferential adsorption of selected 2,3,7,8-substituted congeners on activated carbon injected in the gas stream for mercury removal. These lower molecular weight congeners are typically present in the gas phase and contribute more significantly to the TEF weighted sum.

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