Emissions and carbon isotopic signatures of polycyclic aromatic compounds (PAHs, OPAHs) produced by coking in China.

The coking industry is a major source of polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (OPAHs). Although some OPAHs are considered to be more toxic than PAHs, limited information is available on the levels of PAH and OPAH emissions from the coking industry. Accordingly, we measured the emission factors (EF) for PAHs and OPAHs produced by the coking industry in China. The results revealed that the EFS for PAHs and OPAHs in stack flue gases produced by coal charging, coke pushing, coke quenching, and coke oven gas combustion processes were 1.3-11 and 0.05-0.56 mg/t coke, respectively. Positive correlations were observed between the EFs for selected OPAHs and those for structurally similar PAHs. Among the OPAHs and PAHs examined in this study, the concentration ratios (Ro) ranged between 0.10 and 0.60 (e.g., 0.60 ± 0.76 for ATQ/ANT), which is substantially lower than that in ambient air (e.g., 20.8 for ATQ/ANT), suggesting that the compounds were primarily emitted during coking. The total emissions of PAHs and OPAHs in China in 2022 were calculated to be 9.64 and 0.49 t, respectively. In addition, the stable carbon isotope (δ13C) values of gaseous PAHs were higher than those of particulate PAHs. This finding is attributable to the different formation pathways of gaseous and particulate PAHs and the occurrence of isotopic fractionation during the nucleation of flue gas. No significant differences in the δ13C values of particulate PAHs were observed between the various coking processes.