The main properties of corona discharges are reviewed, with emphasis on the features which make them unique for use as non-equilibrium chemical reactors : Their stability and ease of operation over a wide range of gases and pressures, including atmospheric ; their sharply confined ionization regions where hot electrons interact with cold gas, inducing reactions without back reactions ; and their extended low field drift regions which act as gaseous electrolytes, inducing electrochemical reactions on surfaces. Present and future applications are discussed : Synthesis of ozone and ammonia, promotion of flames and combustion, surface treatment, and electrical insulation improvement.

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A point-plane corona discharge in ambient air is modelled by regarding the drift of ions from the coronating point-electrode to the earthed plane as a succession of non-interacting uniform spheres of charge. Each sphere is thought to expand in its self-field as it drifts in the mean field between point and plane. The space charge deposited by the spheres on their arrival at the plane implies a current distribution which gives an analytic alternative to Warburg's empirical expression. It is shown that the parameters of the model can be adjusted to give a good fit to experimentally obtained results for negative coronas. The success of this simple model is discussed in terms of experimental observations and recent theoretical developments.

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