Levels and particle-size distributions of environmentally persistent free radicals (EPFRs) in haze-associated atmospheric particulate matter (PM) have not been highlighted, even though they may enter the human body along with PM and adversely affect human health. This study quantified the levels of EPFRs in airborne PM with different aerodynamic diameters (d) using electron paramagnetic resonance (EPR) spectroscopy. EPR spectra showed a single, unstructured signal from persistent semiquinone radicals. The average concentration of EPFRs in the airborne PM during haze events was 2.18 × 12 spins/g (range: 3.06 × 10-6.23 × 10 spins/g), approximately 2 orders of magnitude higher than that reported previously in the US atmosphere. Particle-size distributions of EPFRs in four different PM fractions (d > 10 μm, 10 μm < d < 2.5 μm, 2.5 μm

Few studies have investigated the free radical intermediates involved in the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from chlorophenol. This study clarified the reaction pathways during thermochemical formation of PCDDs from 2,3,6-trichlorophenol (TCP) over a Cu(II)O/silica matrix, which was used to simulate fly ash, at 298-523 K. The reaction was studied using electron paramagnetic resonance (EPR) spectroscopy and theoretical calculations. In situ EPR indicated the TCP radical (TCPR) formed by hydrogen abstraction of TCP. Five elementary processes including dimerization of TCPR, ortho-chloride abstraction, Smiles rearrangement, ring closure, and intra-annular elimination of Cl were proposed to occur during formation of PCDDs. The proposed mechanism was further confirmed by the detection of PCDD products from thermochemical experiments in a tube furnace. Several dominant congeners, including 1,2,6,9-tetrachlorodibenzo-p-dioxin (TeCDD), 1,2,6,7-TeCDD, 1,2,8,9-TeCDD, and 1,4,6,9-TeCDD were detected by gas chromatography/quadrupole time-of-flight mass spectrometry, and further confirmed by gas chromatography/high resolution mass spectrometry. The detected PCDD products agree with the proposed PCDD formation mechanism. Relatively high temperatures were found to lead to dechlorination of TCPR to form phenoxy radicals in addition to PCDD/Fs. These radicals will be attached to particles, which will increase their lifetimes. These reactions were further verified by molecular orbital theory calculations. The discovery of persistent phenoxy radicals is of environmental significance because of their potential toxicity. The details of this mechanism could be used for controlling PCDD/F formation during industrial thermal processes.

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The generation of and extent to which chlorinated and brominated polycyclic aromatic hydrocarbons (Cl/Br-PAHs) are formed and released from secondary copper smelters remain unknown. This field study, to our knowledge, is the first to identify secondary copper smelters as new sources of Cl/Br-PAHs. Mass concentrations of ∑Cl-PAHs and ∑Br-PAHs ranged from 5.8 to 271 ng Nm and 0.59 to 52.4 ng Nm, respectively. A comparison of Cl/Br-PAH concentrations in stack gas and fly ash from secondary copper smelters indicated that the use of scrap copper as raw material or the addition of coal or heavy oil as reductant may contribute to the elevated formation and emission of Cl/Br-PAHs. Congener profiles of Cl/Br-PAHs in stack gas and fly ash from secondary copper smelters were different with those of Cl/Br-PAHs from waste incinerations and other previously reported sources, thus could be used as possible fingerprints and source apportionments of environmental Cl/Br-PAHs. Atmospheric levels of Cl/Br-PAHs in the workplace or smelter surroundings were determined and potential exposures were assessed. Although chlorination of PAHs was previously recognized as an important formation pathway of Cl/Br-PAHs, it was not verified to be the major formation pathway for Cl/Br-PAHs from secondary copper smelters in this study.

Several congeners of Cl, Br-PAHs in haze air were reported for the first time.• Cl, Br-PAH levels in heating period were higher than that in non-heating period. • Coal combustion contributes to the elevated levels of Cl, Br-PAHs in heating period.Editor: Jay Gan Profiles, sources and potential exposures of chlorinated and brominated polycyclic aromatic hydrocarbons (ClPAHs and BrPAHs) in haze associated atmosphere remain unclear. Haze events happened frequently during heating period in Beijing provided a typical urban context to investigate the concentrations, profiles, sources and potential exposures of ClPAHs, BrPAHs and their non-halogenated parent compounds (PAHs) in air samples. Average concentrations of PAHs, ClPAHs and BrPAHs during heating periods (with more frequent haze events) were about 3-9 times higher than during non-heating periods. Concentrations of particulate matter (PM)-associated ClPAHs and BrPAHs were higher in heating period than in non-heating period, while for gas-associated ClPAHs and BrPAHs, this distinction was not significant. Congener patterns and congener profiles indicated that with increasing coal combustion during the heating period, concentrations of PAHs and ClPAHs in air were elevated in comparison to the non-heating period. Inhalation of PM-associated PAHs, ClPAHs and BrPAHs accounted for higher exposure than inhalation of gas phase and dermal contact of both gas phase and particulate phase. In this study we found that the particulate phase is the dominant exposure pathway of atmospheric PAHs, ClPAHs and BrPAHs during haze days, which is different from previous studies.

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Photochemical mechanism of persistent free radicals from catechol was clarified Significant free radicals were formed via photochemical reactions of catechol H and O 2 d À were first discovered from the photochemical reactions of catechol This study is important for better recognizing DNA damage of air inhalation of PM 2.5