Absolute partial cross sections for electron impact ionization of nitrogen dioxide (NO2) are determined using Fourier-transform mass spectrometry in the energy range from threshold to 200 eV. Data are presented for the production of the major ionic species, NO2+, NO+, O+, and N+. Ion intensity dependence on the trapping potential is studied for the purpose of probing the kinetic energy of the product ions from the electron impact ionization. O+ and N+ are found to have significant kinetically excited ion populations. The cross-section data are corrected for loss of energetic species from the trap and the results are compared with previous data.