This book presents an experimental investigation of the positive corona under the combined voltage (DC + AC). The dependence of the repetition rate of streamers on DC voltage, AC voltage amplitude and frequency, airflow rate, preionization level, diameter of the point electrode and on the concentration of some electronegative admixtures are recorded. As a result of the present work, a mock-up of a three-gap computer-linked detector of electronegative trace gases is built. The methodology is developed for optimization of parameters of detector such as amplitude and frequency of the AC voltage, DC voltage, airflow rate and preionization level.