This work reports experimental and numerical study of primary jet breakup of a pressure swirl atomizer. Experiments were performed in a constant volume spray chamber and the spray pattern was characterized as a function of different liquid/gas density ratios which was achieved by changing the ambient pressure. The liquid/gas density ratio was varied between ≈ 102 to 103 and the axial Reynold number was maintained at 6x103. Diffused backlight imaging in conjunction with high speed videography was used to visualize the spray. Parameters like spray cone angle, spray breakup length and flapping frequency was estimated. Additionally, POD analysis was performed to find the sheet instability modes. A corresponding numerical study using Coupled Level Set VOF method was performed keeping the liquid/gas density ratio of 10 and 102 to simulate the primary jet breakup using an in-house two-phase solver developed using OpenFOAM libraries. The solver was validated by following the numerical work of Fuster et al. Effect of computational mesh size on parameters like spray cone angle, breakup length was estimated. Copyright © 2019 ASME