An investigation of the way in which naturally-occuring charged particles affect the growth of impulse corona discharges in positive point-plane air gaps is described. The presence of charged particles is shown to be essential for the production of normal branched corona. When a small auxiliary uniform electric field is used to remove charged particles from the gap the discharge fails to propagate beyond the immediate vicinity of the point electrode. It is suggested that the discharge propagates by means of avalanches initiated by electrons which are photodetached from the naturally-occurring charged particles.

No abstract