Sources and gas-particle partitioning of atmospheric parent, oxygenated, and nitrated polycyclic aromatic hydrocarbons in a humid city in southwest China

Polycyclic aromatic hydrocarbons (PAHs) derivatives, such as oxygenated PAHs (OPAHs) and nitrated PAHs (NPAHs), some of which are more toxic and persistent than parent PAHs, have been ubiquitously detected in the environment. Gaseous and particulate PAHs, OPAHs, and NPAHs in the air were measured in an urban environment of Chongqing in southwest China in 2016. Annual average concentrations were 79.9 ± 40.5 ng/m³, 93.7 ± 75.2 ng/m³ and 1.65 ± 1.43 ng/m³ for ∑29 PAHs, ∑10 OPAHs and ∑27 NPAHs, respectively. PAHs had highest level in winter and lowest level in summer while NPAHs and OPAHs showed relatively higher concentrations in summer than spring and autumn, which may be explained by stronger secondary formation of NPAHs and OPAHs in summer. Source apportionment analysis revealed that biomass burning, coal combustion, and petroleum combustion were the main sources for PAHs, while secondary formation, especially in summer, contributed greatly to OPAHs and NPAHs. Gas/particle partition coefficient (logKP) of PAHs, OPAHs and NPAHs, calculated from our observation data, was found to correlate well with the corresponding subcooled liquid vapor pressures (logPLo). The shallower slope of the linear regression between logKP and logPLo for PAHs (−0.61 to −0.52) than OPAHs or NPAHs (−2.14 to −0.73) indicated stronger absorption into the atmospheric particles for PAHs. Three gas/particle partitioning models were evaluated, including the Junger-Pankow adsorption model, the KOA absorption model, and the Dual octanol-air/soot-air model. Compared to the measured values of particle-bound fractions, model predicted values were in reasonable range for PAHs, but were underestimated for NPAHs and OPAHs, suggesting that other important factors such as the influence of RH should be incorporated in gas/particle partitioning models for less hydrophobic compounds, especially in humid areas.