[en] In this article, we report calculations of total ionization cross sections, Q(ion), for simple atoms (C, N, O, F) and molecules (NO and NH₃) of atmospheric interest on electron impact at energies from threshold to 2000 eV. We have employed the complex scattering potential - ionization contribution (CSP-ic) method for the present study. Attempt has been made to improve the method by computing the parameter that involves the ratio of sum of the total excitation cross sections (ΣQ(exc)) and total inelastic cross section (Q(inel)) at the peak of the inelastic cross section. The present study not only provided a better estimation of the parameter involved in the CSP-ic method but also provided better agreement with the available experimental and theoretical data on the ionization cross sections of the simple atomic and molecular targets studied here. (authors)