With increasing gap length, the distance traversed by the ions subject to the electric field decreases. For longer gap lengths, the electric field strength is reduced making the drift velocity of the ions slower. Additionally, the distance that these ions need to traverse to reach the anode is lengthened, increasing the chances for ions to be trapped within the gap after the cycle reversal for the electric field. As the ions have different drift velocities their swarm locations within the gap at the end of the half-cycle varies. This creates alternating areas of high and low concentration of ions. The accumulative charge of the ions in these areas creates distortions in the uniform field. For the low humidity of the plateau phase, the electric field is strong enough to clear most of the O3-, O2- and O- ions within a half-cycle, so the trapped charge remains low. While the trapped charge has a negative effect on breakdown strength of the gap, the reduction of free electrons has a positive one. The nearly flat characteristic of the plateau phase is the product of effects that work in opposition. As the humidity increases the drop phase originates and a progressive reduction in breakdown strength is observed with increasing humidity. This can be explained as follows. The conversion reaction given by equation (5) is a function of humidity and quickly becomes the dominant reaction. The time required for conversion by equation (5) reduces from 32 ns for dry air to 3 ns for humid air, making it faster than detachment processes [9]. Additionally, the large amount of H2O molecules increases the number of conversion reactions taking place by almost an order of magnitude. The heavy ions created by equation (5), O2-⋅(H2O), have a slower drift velocity than that of O-. When conditions are favorable, the O2-⋅(H2O) ions can create clusters with additional water molecules [16]. These clusters are of the form O2-⋅(H2O)x, where x is the amount of water molecules in the cluster [16]. Collision cross-sections of the ionic clusters increase with additional H2O molecules, decreasing their mobility. Also, collision cross-sections of these water clusters vary with the electric field magnitude further hindering their movement [16, 20]. The approximate mobility coefficient for O2-⋅(H2O) obtained is 2.6 cm2/Vs in air [16]. With the given mobility coefficient, the maximum drift distance is 9 mm for a half- cycle of 30 kHz and electric field strength of 22.5 kVrms/cm. For higher humidity, it is probable that a large amount of O2-⋅(H2O)x have not been cleared from the gap before cycle reversal. These trapped charge carriers are responsible for the subsequent reduction in breakdown strength. As the number of O2-⋅(H2O)x ions increase linearly with humidity, the breakdown voltages is reduced until 90% RH is reached.