Temporal trends of atmospheric PAHs: Implications for the gas-particle partition

Abstract

Gas-particle (G/P) partition is the determining factor to the behaviors of semi-volatile organic compounds (SVOCs) in atmosphere, such as transport and deposition. Based on a case study on the measurement of atmospheric polycyclic aromatic hydrocarbons (PAHs) in Harbin City in China from June 2014 to May 2019, the long-term temporal trend of G/P partition of PAHs and its influencing factors were comprehensively studied. The results indicated that an obvious decreasing temporal trend was observed for total suspended particle (TSP) with the annual mean concentrations of 180, 173, 134, 132, and 119 μg/m³ for the five years. The results demonstrated the effectiveness of the Clean Air Action on decreasing TSP levels in Harbin City. For most PAHs, obvious long-term temporal trends and seasonal variations were observed for the particulate phase fraction (φ_P) and the G/P partitioning quotient (K_P) by fitting with a simple harmonic regression method. Significant correlations between φ_P with temperature and TSP indicated their influences on the temporal trend of φ_P. Similarly, the temperature was also the direct influencing factor to the temporal trend of K_P. For the five years, non-obvious differences were observed with the linear relationships between log K_P vs. log K_OA, and between log K_P vs. log P_L. The comparison between the monitoring data of φ_P and log K_P with the prediction data from the G/P partitioning models indicated that the predictions of the models did not well match all the monitoring data for the period. Therefore, more studies should be conducted to better understand the G/P partitioning mechanism of PAHs in atmosphere and to establish more accurate G/P partitioning models. In summary, the results of the present study provided new insight into the G/P partitioning behavior of PAHs in the atmosphere, especially for the temporal trend of φ_P and log K_P.