[Characterization and Source Apportionment of Polycyclic Aromatic Hydrocarbons in PM_2.5 in Lanzhou]

To study the pollution characteristics and sources of 16 PAHs in PM_2.5 in Lanzhou, PM_2.5 samples were collected in four seasons. GC-MS was employed to analyze the concentration of PAHs. Positive matrix factorization(PMF), trajectory cluster, and potential source contribution function(PSCF) were used to identify the sources of PAHs. The results indicated that the average concentration of PAHs in PM_2.5 in Lanzhou decreased in the order of winter[(118±16.2) ng·m^-3]>autumn[(50.8±21.6) ng·m^-3]>spring[(22.2±8.87) ng·m^-3]>summer[(4.65±1.32) ng·m^-3]. The results of correlation analysis showed that PM_2.5 and TPAHs in Lanzhou had an extremely significant negative correlation with temperature; an extremely significant positive correlation with atmospheric pressure; and a poor correlation with wind direction, wind speed, and relative humidity. The proportion of PAHs with 4-5 rings was much higher than that of those with 6 rings and 2-3 rings, with similar results across the four seasons. Source apportionment results illustrated that the contribution of industrial emissions and biomass and natural gas combustion were dominant in spring and summer seasons. Industrial emissions and coal combustion were dominant in autumn and winter, respectively. The vehicle emissions had no significant change across the four seasons. Trajectory cluster and PSCF analyses showed that the airflow coming from Mongolia, northeast Xinjiang, and Qinghai had important effects on the ambient air quality in Lanzhou.