[Seasonal Variation and Source Apportionment of Carbonaceous Species in PM_2.5 in Chengde]

In order to study the seasonal variations and pollution sources of carbonaceous species in PM_2.5 in Chengde, the concentration of these components was determined in atmospheric PM_2.5 samples collected in January, April, July, and October 2019. The change in carbonaceous species were analyzed based on the estimation of the ratio of organic carbon(OC) to elemental carbon(EC), total carbonaceous aerosol(TCA), and secondary organic carbon(SOC). The source of these pollutants was determined by means of the backward trajectory and principal component analysis(PCA). The results showed that the mean mass concentrations of PM_2.5, OC, and EC during the sampling period were(31.26±21.39) μg·m^-3,(13.27±8.68) μg·m^-3, and(2.80±1.95) μg·m^-3, respectively. The seasonal variations of PM_2.5 were:winter[(47.68±30.37) μg·m^-3]>autumn[(28.72±17.12) μg·m^-3]>spring[(26.59±15.32) μg·m^-3]>summer[(23.17±8.38) μg·m^-3], consistent with the trend of total carbon(TC), OC, and EC. The source of OC and EC during winter(R²=0.85) was similar. Based on the ratio of OC/EC, all four seasons were affected by traffic and coal-burning source emissions, and the most affected season by bituminous coal emissions was winter. The average concentration of TCA was(21.38±13.68) μg·m^-3, which accounted for 68.39% of PM_2.5. The order of secondary conversion rate(SOC/OC) was:spring(54.09%) >autumn(37.64%) >summer(32.91%) >winter(25.43%). The results of the backward trajectory simulation show that the pollutant concentrations carried by air masses are relatively low in spring and summer, and the transport channels of pollutants are southwest in autumn and northwest in winter. The results of the PCA showed that the key to reducing PM_2.5 in Chengde is to control emissions from vehicle exhausts, and coal and biomass combustion sources.