The effects of SO2 emission, which is one of the most important emission gases caused by ships passing through Strait of Istanbul are investigated numerically by means of environmental effects. The numerical analyses are performed by using a commercial CFD (Computational Fluid Dynamics) code solving RANSE (Reynolds Averaged Navier-Stokes Equations). A 100 meters heighted air zone over the Strait of Istanbul is modeled in 3-D and analyses are carried out for unsteady and steady cases and different wind directions. SO2 emission distributions at different heights are obtained. The numerical results gathered by statistical data provide a basis for the authorities in taking precautions, setting up regulations and applying the related regulations of MARPOL Annex VI. The method used for emission estimation in Strait of Istanbul can also give short-term predictions for different scenarios.