: By discharging nanosecond high voltage pulses (up to 25kV) across an insulating substrate coated with metal nanoparticles (Au or Pt), significantly enhanced plasma generation is observed through local field enhancement on the surface of the nanoparticles. The structural integrity of metal nanoparticles can be maintained due to the low-temperature nature of this transient plasma. Electrostatic simulations based on high-resolution transmission electron microscope (HETEM) image of the nanoparticles demonstrate a 3-fold enhancement of the electric field near the nanoparticle surfaces. Since field emission of electrons, which initiates plasma generation, depends exponentially on electric field, this 3-fold increase in the local electric field can significantly enhance plasma generation at a given applied external voltage. Similar enhancement was also observed by discharging in a methane environment, revealing a 50X enhancement in methane upconversion to C2 and higher order hydrocarbons, presenting the exciting possibility of converting a notorious greenhouse gas into an energy dense hydrocarbon fuel. Under laser irradiation, we observe a 200-fold enhancement in the plasma emission intensity, indicating the important role that hot electrons play in the electron emission process. In addition to gas phase plasma discharge, we also demonstrate CO2 reduction to CO and higher order hydrocarbons by discharging nanosecond high votlage pulses in CO2-saturated water, as revealed by C2 Swan band emission, cryogenic NMR spectroscopy and liquid ion chromatography, which indicate clear peaks corresponding to formic acid, methanol, and acetic acid.