Characteristics and source analysis of carbonaceous component concentration in PM_2.5 in autumn in Qinhuangdao City

To investigate the characteristics and sources of carbonaceous aerosols in Qinhuangdao City during autumn, PM2.5 samples were collected from October 14 to November 2. Organic carbon (OC) and elemental carbon (EC) were quantified using an OC/EC analyzer. The daily average concentrations of PM2.5, OC, and EC were (44.04±33.25) μg·m−3, (8.15±3.70) μg·m−3, and (0.70±0.17) μg·m−3, respectively. OC and EC contributed 24.57% and 2.53% to the PM2.5 mass, respectively. Concentrations of these components were higher at night compared to daytime, and the levels were elevated on polluted days relative to clean days. The average value of OC/EC ratio was 11.14±2.86, and secondary organic carbon (SOC) concentrations, estimated via the OC/EC minimum ratio method, averaged (3.74±2.73) μg·m−3. SOC accounted for 30.65% and 47.94% of OC during the day and night, respectively, and 6.24% and 10.29% of PM2.5 during the same periods. SOC concentrations and their relative contributions to OC and PM2.5 were notably higher at night, indicating more severe SOC pollution during nighttime. Source apportionment using principal component analysis (PCA) and positive matrix factorization (PMF) models identified the major contributions to carbonaceous components in PM2.5 during autumn in Qinhuangdao City. These included gasoline vehicle exhaust (25.8% during the day; 31.3% at night), diesel vehicle exhaust (24.7% during the day; 31.3% at night), biomass burning (13.9% during the day; 20.7% at night), and coal combustion (14.3% during the day; 12.6% at night). Dust sources were more significant during the day, while diesel vehicle emissions and biomass burning contributed more at night.