NOVELTY - A surface discharge non-thermal plasma reactor comprises surface discharge non-thermal plasma reactor elements arranged in a stack; and surface discharge gap formed via spacers disposed between adjacent pairs of the reactor elements.    USE - For treating nitrogen-containing gas stream, e.g. air.    ADVANTAGE - The invented surface discharge non-thermal plasma reactor achieves an energy density of over 400 Townsend in the discharge region.    DETAILED DESCRIPTION - A surface discharge non-thermal plasma reactor comprises surface discharge non-thermal plasma reactor elements arranged in a stack; and surface discharge gap formed via spacers disposed between adjacent pairs of the reactor elements. The reactor elements comprise dielectric substrate; surface discharge electrode disposed on the dielectric substrate; and second opposite polarity surface discharge electrode disposed on the dielectric substrate. The first and second polarity surface discharged electrodes are disposed on the dielectric substrates in a pattern providing a surface discharge to selectively control production of nitric oxide from a nitrogen-containing gas stream treated in the reactor. INDEPENDENT CLAIMS are also included for:    (a) a combustion exhaust treatment system (70) comprising an air supply and a power supply connected to the surface discharge non-thermal plasma reactor; hydrogen source for supplying hydrogen to an exhaust stream (80) of the reactor to generate an ammonia containing exhaust stream via a first catalyst; and second catalyst connected to a combustion device for receiving a combustion exhaust stream and connected to the ammonia-containing exhaust stream, where during operation, an air stream is treated in the surface discharge non-thermal plasma reactor to generate a surface discharge nitrogen oxide-containing exhaust combined with hydrogen from the hydrogen source and fed to the first catalyst to generate ammonia that is fed into the second catalyst to be used as a co-reductant for treating the combustion exhaust stream treated in the second catalyst to provide a catalyst treated exhaust stream having nitrogen gas, water, oxygen, carbon dioxide or oxygen gas; and    (b) a method for fabricating a surface discharge non-thermal plasma reactor comprising arranging reactor elements to form a reactor stack; disposing the reactor elements in the stack and placing spacers to provide a surface discharge gap between adjacent pairs of the reactor elements; forming individual reactor elements by providing a dielectric substrate; disposing first polarity surface discharge electrode on the dielectric substrate; and disposing a second opposite polarity surface discharge electrode on the dielectric substrate.    DESCRIPTION OF DRAWING(S) - The figure is a block schematic diagram of an engine exhaust treatment system.    Combustion exhaust treatment system (70)    Exhaust stream (80)