Global Simulation of Polycyclic Aromatic Hydrocarbons (PAHs) with the CHASER Chemistry–Climate Model

To resolve thermodynamic uncertainties in global gas–particle partitioning and persistent organic pollutant transport, this work integrates polycyclic aromatic hydrocarbons (PAHs) into the CHASER V4.0 chemistry–climate model, presenting the first global online simulations of naphthalene (NAP), phenanthrene (PHE), pyrene (PYR), and benzo[a]pyrene (BaP) within this framework to study their fate in the atmosphere. Soot adsorption (KSA(T)) is coupled with organic matter absorption (KOA(T)) under an extended Dachs–Eisenreich dual-mode scheme. The coupled model was evaluated at urban, background, and Arctic stations, satisfactorily capturing the broad global spatial gradients (pooled spatial R = 0.78 on a log10 scale; spatial FAC2 = 80% for BaP excluding severe sub-grid hotspots) and seasonal cycles (R = 0.62–0.93). The KSA(T) scheme rectifies the under-prediction of the particle-bound fraction (φ) in cold high-latitude regions (increasing polar φBaP by up to ~0.6), inherent in the baseline KOA(T) scheme. Sensitivity tests show that elevated elemental carbon (fEC) enhances soot adsorption and particle-phase shielding against oxidation, extending the mean lifetime of BaP to 1.72 days (compared to 0.57–0.72 days for lighter congeners) and sustaining transoceanic outflow. Overall, this framework provides an essential tool for assessing transboundary toxicant transport, climate-sensitive health risks, and pollution mitigation policies.