The ion swarm data such as reduced mobilities, diffusion coefficients and reaction rates of N4+ in N2, O2 and dry air (80% N2, 20% O2) have been determined from a Monte Carlo simulation using calculated and measured elastic and inelastic cross sections. The elastic cross sections used have been determined from a semi-classical JWKB approximation based on a rigid core potential model. The inelastic cross section of N4+ in N2 has been deduced from the measured experimental rates whereas for N4+ in O2 the measured inelastic cross sections have been extended to low and high energies by appropriate approximations. Then the cross sections sets have been validated from comparison of calculated and measured ion swarm data. From the cross sections sets obtained in pure N2 and O2, the ion swarm data for N4+ in dry air are then calculated for a large E/N range [1–104] Td. Finally, the influence of N4+ ions on the streamer development was analyzed with a 2D fluid model in the case of dry air at atmospheric pressure for a point-to-plane electrode configuration.