This paper presents a new approach to model the pesticide atomization in order to get the droplet size and velocity very close to the nozzle exit. The two-phase flow was calculated inside and outside the nozzle. The model was based on classical fluid mechanics transport equations for the liquid dispersion, velocity and turbulence. Moreover, a novel transport equation was developed for the mean liquid/gas surface area, coming from studies in automotive and aeronautics fields. Coupling the transport equations for the liquid mass fraction and the surface area led to an estimation of a Sauter Mean Diameter. These equations have been implemented in the commercial CFD code Fluent. A swirling flow was found inside the nozzle. Moreover, a hollow cone liquid sheet expanded outside the nozzle. Calculations have been conducted with various injection pressure values, leading to a mass flow rate in good accordance with manufacturer data. Surfactant influence has been studied by varying the surface tension coefficient in the surface area transport equation: as expected, droplets obtained are smaller than when water is considered.