Ozone Oxidation of the Flame Retardant BDE-209: Kinetics and Molecular-Level Analysis of the Gas-Phase Product Compounds

Abstract

Polybrominated diphenyl ether (PBDE) flame retardants are persistent organic pollutants that are ubiquitous in both indoor and outdoor environments and exhibit adverse health effects. Among all of the PBDEs, decabromodiphenyl ether (BDE-209) is the most abundant due to the increased production of electronic devices. Here we evaluate the uptake coefficients of ozone (O₃) on glass plates coated with BDE-209 at different relative humidities (RH) over a range of temperatures. The uptake of O₃ slightly increased with the increase of RH from 1.2 × 10^–5 at 30% RH to 2.2 × 10^–5 at 90% RH, but was independent of the temperature change. Real-time measurements of the gas-phase product compounds formed by the reaction of O₃ with BDE-209 were performed with a high-resolution Q Exactive hybrid quadrupole Orbitrap mass spectrometer (UHR-MS) in both positive and negative ionization modes. Interestingly, the molecular-level analysis revealed that the observed gas-phase product compounds in the presence of water vapor did not contain Br atoms and, in most cases, had fewer than 12 C atoms, indicating that both debromination and aromatic ring fragmentation occurred. The developed reaction mechanism suggests that the formation of most CHO compounds occurs by the combination of reductive debromination triggered by HO₂ with ring and open-chain fragmentation induced by O₃. The molecular-level understanding of the volatile product compounds produced by the ozonolysis of glass coated with BDE-209 provides valuable insights into the reaction mechanism, enabling more accurate characterization in atmospheric model studies.