# Ship Route Oil Spill Modeling: A Case Study of the Northeast Brazil Event, 2019
## 4 Discussion
The chemical transformations of oil must be thoroughly understood to gain a more precise understanding of its chemical behavior in the sea, and processes such as evaporation, spreading, dissolution, and emulsification represent the primary transformation processes on a smaller time scale. A physicochemical understanding of transformation allows for an assessment of the possibility and spatio-temporal scale of oil sinking to the subsurface, which hinders environmental cleanup, as well as the surface area coverage of oil in the sea. This combined information is crucial for emergency teams dedicated to oil recovery at sea and for onshore teams responsible for cleaning up any material that reaches the coast. Probabilistic spill scenarios are useful for emergency teams as they consider different spill conditions within a single deterministic scenario, such as the oil release rate and the initial simulation date, with the aim of encompassing different simulation conditions within that scenario and identifying the probabilities of oil presence in certain compartments (e.g., surface or shoreline) and regions. The use of probabilistic simulations is also beneficial in cases where the initial spill conditions are unknown [51]. This approach was employed by [13] at different points near the Brazilian coast. The results for Location D are particularly notable, as this location is considered the western limit of the possible spill source area and encompasses the starting point of the probabilistic simulation of the mobile source in experiment 22 (12\({}^{\circ}\) S; 31.8\({}^{\circ}\) W) in a northeast direction, located in the northwest portion of the polygon identified by [34]. Considering the non-floating oil drift, [13] found an intermediate level of confidence for Location D and reported that, within the delimited area, the chosen point (11\({}^{\circ}\) S, 33\({}^{\circ}\) W) is too close to the coast to be representative of the event. However, experiment 22 has its initial spill point further south and offshore, lasting 7.1 h and ending at 11.3\({}^{\circ}\) S and 31.5\({}^{\circ}\) W, being farther away from the coast and potentially reaching the shoreline by the end of August. The probabilistic simulation of experiment 22 demonstrated extensive oil spreading toward the northern and southern coasts (Figure 6), with a higher probability of oil reaching the coast (>50%) between 6\({}^{\circ}\) S and 12\({}^{\circ}\) S. In this simulation, the oil spread could reach the northern region of Rio de Janeiro State (RJ) (at approximately 22\({}^{\circ}\) S), albeit with a lower probability (0-10%). The arrival occurred on the southern coast of Paraiba State (PB) 17 days after the beginning of the spill, which is consistent with the observations according to IBAMA data. Despite these results, it is known that there are many gaps within the study, with one of the most significant being the resolution of the meteo-oceanographic forcings. To accurately combine the spatiotemporal arrival of oil on the coast, forcings with kilometer-scale spatial resolutions are not the most appropriate; therefore, future studies should improve this resolution to the scale of hundreds or tens of meters to gain a more precise understanding of the coastal environments affected by a spill.