of ionizing inelastic collision at common temperatures and pressures. An important reason for considering coronas is the production of ozone around conductors undergoing corona processes in air. A negative corona generates much more ozone than the corresponding positive corona. Applications Corona discharge has a number of commercial and industrial applications: Removal of unwanted electric charges from the surface of aircraft in flight and thus avoiding the detrimental effect of uncontrolled electrical discharge pulses on the performance of avionic systems Manufacture of ozone Sanitization of pool water In an electrostatic precipitator, removal of solid pollutants from a waste gas stream, or scrubbing particles from the air in air-conditioning systems Photocopying Air ionisers Production of photons for Kirlian photography to expose photographic film EHD thrusters, lifters, and other ionic wind devices Nitrogen laser Ionization of a gaseous sample for subsequent analysis in a mass spectrometer or an ion mobility spectrometer Static charge neutralization, as applied through antistatic devices like ionizing bars Refrigeration of electronic devices by forced convection Coronas can be used to generate charged surfaces, which is an effect used in electrostatic copying (photocopying). They can also be used to remove particulate matter from air streams by first charging the air, and then passing the charged stream through a comb of alternating polarity, to deposit the charged particles onto oppositely charged plates. The free radicals and ions generated in corona reactions can be used to scrub the air of certain noxious products, through chemical reactions, and can be used to produce ozone. Problems Coronas can generate audible and radio-frequency noise, particularly near electric power transmission lines. Therefore, power transmission equipment is designed to minimize the formation of corona discharge. Corona discharge is generally undesirable in: Electric power transmission, where it causes: Power loss Audible noise Electromagnetic interference Purple glow Ozone production Insulation damage Possible distress in animals that are sensitive to ultraviolet light Electrical components such as transformers, capacitors, electric motors, and generators: Corona can progressively damage the insulation inside these devices, leading to equipment failure Elastomer items such as O-rings can suffer ozone cracking Plastic film capacitors operating at mains voltage can suffer progressive loss of capacitance as corona discharges cause local vaporization of the metallization In many cases, coronas can be suppressed by corona rings, toroidal devices that serve to spread the electric field over a larger areas and decrease the field gradient below the corona threshold. Mechanism Corona