Atmospheric Characterization of Legacy and Emerging Flame Retardants in the Canadian Arctic and Great Lakes Basin

Atmospheric concentrations of flame retardants (FRs)─including polybrominated diphenyl ethers (PBDEs) and non-PBDE halogenated flame retardants (HFRs)─were assessed using long-term measurements from two remote Canadian locations: Alert (2002–2019) in the High Arctic and Point Petre (2005–2022) in the Great Lakes region. Organophosphate esters (OPEs) were additionally characterized at Point Petre. At Alert, PBDE concentrations declined with estimated half-lives of 4–9 years, consistent with regulatory phase-outs under the Stockholm Convention. However, slight increases in PBDE concentrations after ∼2014 suggest revolatilization from local surfaces. Non-PBDE HFRs such as Dechlorane Plus were detected at both sites, but low detection frequencies precluded trend analysis. At Point Petre, PBDEs also showed a declining trend, with an estimated half-life of 6.60 years for Σ15PBDEs, while OPEs measured from 2018 to 2022 were frequently detected, often at higher concentrations than PBDEs and non-PBDE HFRs. Gas–particle partitioning of OPEs was evaluated using field-derived particle-phase fractions and compared to model predictions. Substantial discrepancies, especially for low molecular weight OPEs, suggest that current models may misrepresent their atmospheric behavior, partly due to omission of activity coefficients that influence sorption. These findings highlight the shifting profiles of flame retardants in remote air and point to the need for improved models that account for physicochemical factors governing their atmospheric behavior.