DC discharges in atmospheric air and their transitions

We present images and basic characteristics and describe transition mechanisms between three do discharges in atmospheric air point-to-plane or point-to-water gap. With increasing applied voltage, a streamer corona transits to a transient spark: a repetitive spark with very short (similar to 100-ns) current pulses (similar to 1 A) of very limited energy. With an appropriate ballast resistor, this transient regime evolves into a pulseless glow discharge. These three discharges generate nonequilibrium plasmas of high chemical activity interesting for environmental and biomedical applications.