This paper reports efficient treatment of diesel emission with transient, non-equilibrium plasma created by a pulsed corona discharge. The transient plasma (∼50 ns) is found to reduce NOx emission in a flow of 1-10 liters/ second with energy cost ≤10-20 eV/molecule, corresponding to a fraction of source power of ∼5%. The efficiency of NOx reduction is a complex function of parameters that include pulse width, pulse polarity, current density, repetition rate, and reactor design. It was found that best efficiencies are correlated with a low current density (0.2A/cm2) and high repetition rate (1kHz) under high flow rate. Careful optimization of all these parameters is required to reach cost effective NOx reduction.