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Tailoring the chemical environment in plasmas by addition of reactive gases to affect byproduct formation has been demonstrated to reduce perfluorocompound (PFC) emissions. Perfluorocompound emissions from dielectric etch processes are reduced by oxygen addition, which reduces polymerization and increases etch rates, primarily by affecting the fluorine or carbon in the plasma, and secondarily, by affecting resist erosion. Oxygen or water vapor introduced upstream of plasma abatement devices reduces PFC reformation by preferentially combining with carbon and fluorine-containing radicals to form thermodynamically favorable byproducts that are non- or low-global warming. Introducing oxygen to low-k chemical vapor deposition (CVD) chamber clean processes also reduces PFC emissions, primarily by reducing CF4 by forming thermodynamically stable CO and CO2. Analogously, adjusting the fuel or the oxidizer flow in fuel-fired abatement devices provides a higher flame temperature where thermal cracking of higher molecular weight low-k CVD organosilicon precursors can more readily occur, allowing the carbon-rich precursors to more completely oxidize.