Ozone\nOxidation of the Flame Retardant BDE-209: Kinetics\nand Molecular-Level Analysis of the Gas-Phase Product Compounds

Polybrominated diphenyl ether (PBDE) flame retardants\nare persistent\norganic pollutants that are ubiquitous in both indoor and outdoor\nenvironments and exhibit adverse health effects. Among all of the\nPBDEs, decabromodiphenyl ether (BDE-209) is the most abundant due\nto the increased production of electronic devices. Here we evaluate\nthe uptake coefficients of ozone (O<sub>3</sub>) on glass plates coated\nwith BDE-209 at different relative humidities (RH) over a range of\ntemperatures. The uptake of O<sub>3</sub> slightly increased with\nthe increase of RH from 1.2 × 10<sup>–5</sup> at 30% RH\nto 2.2 × 10<sup>–5</sup> at 90% RH, but was independent\nof the temperature change. Real-time measurements of the gas-phase\nproduct compounds formed by the reaction of O<sub>3</sub> with BDE-209\nwere performed with a high-resolution Q Exactive hybrid quadrupole\nOrbitrap mass spectrometer (UHR-MS) in both positive and negative\nionization modes. Interestingly, the molecular-level analysis revealed\nthat the observed gas-phase product compounds in the presence of water\nvapor did not contain Br atoms and, in most cases, had fewer than\n12 C atoms, indicating that both debromination and aromatic ring fragmentation\noccurred. The developed reaction mechanism suggests that the formation\nof most CHO compounds occurs by the combination of reductive debromination\ntriggered by HO<sub>2</sub> with ring and open-chain fragmentation\ninduced by O<sub>3</sub>. The molecular-level understanding of the\nvolatile product compounds produced by the ozonolysis of glass coated\nwith BDE-209 provides valuable insights into the reaction mechanism,\nenabling more accurate characterization in atmospheric model studies.