Variations in polycyclic aromatic hydrocarbons and nitro polycyclic aromatic hydrocarbons in diesel vehicle emission plumes

Comprehensive investigation into the atmospheric behavior of polycyclic aromatic hydrocarbons (PAHs) and nitro polycyclic aromatic hydrocarbons (NPAHs) is essential for mitigating air pollution and reducing health risks. This study conducted real-world tests on 21 diesel vehicles to characterize the gas-particle partitioning behavior of PAHs and NPAHs in exhaust plumes, considering the effects of vehicle types, emission standards, and operating conditions. Results indicate that the relative factors of total (gas + particle phase) PAHs and NPAHs to carbon dioxide (CO2) in exhaust plumes remain largely stable, although their compositional distributions vary. The particle-phase percentages of PAHs and NPAHs increased by 41.18 % and 41.85 %, respectively, from sampling channel #1 to #4, suggesting that dilution promotes the phase transition of PAHs and NPAHs from the gas to the particle phase. PAHs and NPAHs were also found to significantly contribute to secondary organic carbon (SOC) formation, reaching maximum proportions of 22.13 % +/- 12.30 % and 22.66 % +/- 18.73 %, respectively, during dilution. The contributions of PAHs and NPAHs to SOCs initially decline and then recover with increasing distance, possibly due to the stabilization of gas-particle partitioning or the formation of secondary compounds. These findings enhance the understanding of the atmospheric behavior of PAHs and NPAHs, provide empirical data for modeling, and offer a scientific basis for pollution control.