High-fidelity numerical simulations of spray formation were conducted with the aim of improving fundamental understanding of airblast liquid-film atomization. The gas/liquid interaction in the near-nozzle region is investigated for a multitude of operating conditions in order to extrapolate phenomenological and breakup predictions. To reach this goal, the robust conservative level-set (RCLS) method was used. For a fixed prefilmer geometry, we performed a parametric study on the impact of various liquid and gas velocities on the topological evolution of the liquid interface. The behavior and development of the liquid film is found to be influenced mainly by the relative inertia of the gas and the liquid, the liquid surface tension, and interfacial shear stresses. Preliminary regime maps predicting the prefilming liquid-sheet atomization behavior are constructed based on our numerical results. Three distinct types of "regime" are reported: accumulation, ligament-merging, and three-dimensional wave mode. In addition, these results also show the influence of vortex action and rim-driven dynamics on the breakup mechanism at the atomizer edge. An increase in liquid injection speed leads to the generation of smaller droplets; whereas, an increase in air velocity does not point to one simple conclusion.