Hot and Cold: Photochemical Weathering Mediates Oil Properties and Fate Differently Depending on Seawater Temperature

Photochemical weathering transforms petroleum oil andchanges itsbulk physical properties, as well as its partitioning into seawater.This transformation process is likely to occur in a cold water marineoil spill, but little is known about the behavior of photochemicallyweathered oil in cold water. We quantified the effect of photochemicalweathering on oil properties and partitioning across temperatures.Compared to weathering in the dark, photochemical weathering increasesoil viscosity and water-soluble content, decreases oil-seawaterinterfacial tension, and slightly increases density. Many of thesephotochemical changes are much larger than changes caused by evaporativeweathering. Further, the viscosity and water-soluble content of photochemicallyweathered oil are more temperature-sensitive compared to evaporativelyweathered oil, which changes the importance of key fate processesin warm versus cold environments. Compared to at 30 & DEG;C, photochemicallyweathered oil at 5 & DEG;C would have a 16x higher viscosityand a 7x lower water-soluble content, resulting in lower entrainmentand dissolution. Collectively, the physical properties and thus fateof photochemically weathered oil in a cold water spill may be substantiallydifferent from those in a warm water spill. These differences couldaffect the choice of oil spill response options in cold, high-lightenvironments. Sunlight-driven weatheringchanges oil transport, fate,and response effectiveness during a spill at sea. Our findings demonstratethat these changes depend strongly on temperature.

Automated summary

Photochemical weathering changes the properties of petroleum oil, especially in cold water environments. Compared to weathering in the dark, photochemical weathering increases oil viscosity and water-soluble content, decreases oil-seawater interfacial tension, and slightly increases density. The physical properties and fate of photochemically weathered oil in a cold water spill may be significantly different from those in a warm water spill, which could impact oil spill response options.