Corona Quenching occurs in electrostatic precipitators with high aerosol concentrations and leads to a reduced current uptake and a high emission of particles. The phenomenon of corona quenching is investigated both theoretically and experimentally. It appears that corona quenching is not a disturbance, but a special mode of operation which is very efficient for the separation of particles. However, quenched electrostatic precipitators need to be designed and optimized according to their own rules.