Concentration of total target polycyclic aromatic hydrocarbons (PAHs) per milligram of weathered oil initially added to the microcosm flask: Four different weathering experiments, oil in artificial seawater (OAS), oil augmented with dispersant in artificial seawater (OASD), oil in natural seawater (ON), and oil augmented with dispersant in natural seawater (OND). The weathering experiments were run for 28 days, and microcosm flasks were extracted at days 0, 0.5, 3, 7, 14, 21 and 28.