Positive streamers in ambient air and a N2:O2-mixture (99.8 : 0.2)
  Photographs show distinct differences between positive streamers in air or in a nitrogen-oxygen mixture (0.2% O2). The streamers in the mixture branch more frequently, but the branches also extinguish more easily. Probably related to that, the streamers in the mixture propagate more in a zigzag manner while they are straighter in air. Furthermore, streamers in the mixture can become longer; they are thinner and more intense. 
T.M.P. Briels, E.M. van Veldhuizen, Ute Ebert