Diagnostic parameters for coal-source polycyclic aromatic hydrocarbons and their environmental validation

Polycyclic aromatic hydrocarbons (PAHs) released into the environment from unburned coal are challenging to distinguish from combustion or petroleum sources, thereby compromising accurate source apportionment and subsequent ecological risk assessment. To establish diagnostic ratios capable of effectively distinguishing coal-source PAHs, this study investigated published datasets with more than 100 reference samples on PAHs and alkylated PAHs present in coal and coal gangue and constructed four sets of diagnostic ratio indicators for coal sources. These ratios were validated using 58 environmental samples comprising surface soils and dust collected from an abandoned coal mining area and reference coal and coal gangue samples obtained from the mine. The constructed diagnostic ratios and corresponding thresholds were: 0.5 < (Nap + C₁-Nap)/C₂-Nap < 5.0; 0.7 < C₁-PhA/(Phe + Ant) < 2.6; C₁-FlP/Pyr > 0.4 and C₁-FlP/(Fla + Pyr) > 0.5; and ∑₁₆PAH/∑aPAH < 1 and 0.4 < Fla/(Fla + Pyr) < 0.6. Source identification based on PAH concentrations, molecular fingerprints, ring number composition, and the distribution patterns of alkyl-substituted homologues clearly distinguished the origins of PAHs in the contaminated soil and dust samples as coal, combustion, and a mixed coal-residential combustion sources. The results obtained using the newly established diagnostic ratios were consistent with those obtained using traditional source identification methods. The proposed diagnostic ratios effectively distinguished coal-source PAHs from petroleum- and combustion-derived PAHs, enabling precise identification of PAH pollution sources in complex surface environments.