Major Missing Source of Alkylated Polycyclic Aromatic Hydrocarbon Emissions from Oil Spill Volatilization

Alkylated polycyclic aromatic hydrocarbons (APAHs) often possess higher toxicity than their parent compounds, yet global inventories largely overlook their direct volatilization from crude oil spills. To quantify this missing pathway, we developed a Monte Carlo framework that estimates this non-combustion source by coupling empirical spill statistics, APAH composition from 18 crude oils, and marine/terrestrial volatilization efficiencies. Across eight validated volatile species (C1-C4 naphthalenes, C1 phenanthrenes, C1-C3 fluorenes), global emissions span 3.4-73.4 kt/year (95% confidence interval), with a median of ∼17.5 kt/year. Notably, methylnaphthalenes (MeNAPs) alone account for ∼5.9% of their known global atmospheric emissions. Although global inventories for other homologues are unavailable, absolute fluxes of C2-C4 naphthalenes are comparable to or exceed MeNAPs, underscoring oil spills as a substantial, previously unquantified source of light APAHs. Sensitivity analyses highlight key uncertainties in spill volumes, crude compositions, and volatilization ratios; assumptions of parameter independence may understate extreme events. It is important to note that, due to the exclusion of dynamic meteorological suppression factors (e.g., low temperature and calm winds), these estimates represent a potential source strength. Incorporating this non-combustion pathway into inventories is therefore critical for accurate environmental risk assessments and regulatory policies.