Kinetic Aerosol Trapping Drives Arctic Enrichment of Organophosphate Flame Retardants.

Organophosphate flame retardants (OPFRs) are emerging contaminants posing significant risks to the Arctic environment and human health. Concerns have been raised about the origins of Arctic OPFRs because atmospheric models have failed to reproduce the high Arctic OPFR levels due to unresolved phase-partitioning dynamics and atmospheric chemistry. Here, we implement a kinetic gas-particle accumulation scheme, in which particle-bound OPFRs do not re-equilibrate to the gas phase, into the atmospheric chemistry model GEOS-Chem High Performance (GCHP) v14.5.0. A 2 × 2 factorial design crossing the partitioning mechanism with hydroxyl radical (OH) chemistry isolates the importance of each process. In the Arctic, kinetic accumulation reduces the apparent OH removal efficiency from 79% under equilibrium partitioning to 64%. The corresponding atmospheric lifetime of ΣOPFRs is extended from 1.0 day under gas-phase-only conditions to 9.8 days under the kinetic accumulation framework. Sulfate and hydrophilic organic carbon together carry over 90% of the Arctic particulate OPFR burden. This kinetic scheme increases the simulated Arctic annual mean ΣOPFR concentration from 82 pg m-3 under gas-phase-only conditions and 145 pg m-3 under instantaneous equilibrium to 353 pg m-3, representing 4.3-fold and 2.4-fold increases, respectively, consistent with field measurements across the Arctic.