The Kuroshio Regulates the Air–Sea Exchange of PCBs in the Northwestern Pacific Ocean

Calculating accurate air–sea fluxes for polychlorinated biphenyls (PCBs) is an essential condition for evaluating their transport in the atmosphere. A three-dimensional hydrodynamic-ecosystem-PCB coupled model was developed for the northwestern Pacific Ocean to assess the air–sea fluxes of four PCBs and examine the influences of ocean currents on the fluxes. The model revealed a fine structure in the air–sea flux that is sensitive to the Kuroshio, a western boundary current with a high surface speed. Intense downward and upward fluxes (−23.6 to 44.75 ng m–2 d–1 for ∑4PCBs) can be found in the Kuroshio region south of Japan and the Kuroshio Extension east of Japan, respectively. In strong (weak) current regions, it takes ∼4 and ∼1 days (1–3 and 3–12 days) for dissolved PCBs to reach an equilibrium in scenarios where only air–sea exchange or only ocean advection is considered, respectively. In strong current regions, the ocean advection has a shorter response time than the air–sea exchange, indicating that dissolved PCBs from upstream carried by strong current can easily change the downstream concentration by disrupting the equilibrium with original air–sea exchange and induce new air–sea fluxes there. Therefore, strong western boundary currents should be correctly considered in future atmospheric transport models for PCBs.