Non-equilibrium influence on G/P partitioning of PAHs: Evidence from the diurnal and nocturnal variation

Gas/particle (G/P) partitioning is an important behavior for the atmospheric transport of polycyclic aromatic hydrocarbons (PAHs). In this study, paired daytime and nighttime air samples were collected for one year in order to study the diurnal and nocturnal variations of concentration and G/P partitioning of PAHs. Higher PAHs concentrations in total phase were observed in nighttime. The geomean (GM) concentrations of sigma 15PAHs in total phase were 69.6 and 52.8 ng/m3 in nighttime and daytime, respectively. More obviously diurnal and nocturnal variations were observed in non-heating season, with the GM ratios of sigma 15PAHs in nighttime to daytime of 1.65 and 1.06 in non-heating season and heating season, respectively. The results could be attributed to emission sources and meteorological conditions. The values of particulate phase fraction (phi P) and G/P partitioning quotient (log KP) were used to quantify the phase distribution of PAHs. For most high molecular weight PAHs, the values of phi P and log KP in nighttime were higher than those in daytime, which could be mainly attributed to the lower temperature in nighttime. However, for the three light molecular weight PAHs (Acy, Ace and Flu), higher values of phi P and log KP were observed in daytime. The regression of log KP against log KOA for the three PAHs in daytime differed from those in nighttime. The chemical losses of PAHs in different phases might be responsible for the result. These findings suggested that the chemical loss of PAHs in gas phase should be considered for the G/P partitioning process.

Automated summary

Gas/particle (G/P) partitioning is an important factor for the atmospheric transport of polycyclic aromatic hydrocarbons (PAHs). This study investigated the diurnal and nocturnal variations of PAHs concentration and G/P partitioning by collecting air samples throughout the year. The results showed higher PAHs concentrations in the nighttime total phase, with more pronounced diurnal and nocturnal variations observed in the non-heating season. These variations were attributed to emission sources and meteorological conditions. The study also found that the values of particulate phase fraction and G/P partitioning quotient varied between daytime and nighttime for different molecular weight PAHs. Chemical losses in different phases were suggested to be responsible for these variations. These findings highlight the importance of considering the chemical loss of PAHs in the gas phase during the G/P partitioning process.