[Characterization and Size Distribution of Carbonaceous Aerosols at Mountain Dinghu]

To understand the characterization and sources of carbonaceous aerosols at Mountain Dinghu, organic carbon (OC) and elemental carbon (EC) in size-resolved aerosol samples were measured at a regional background site in South China using a DRI Model 2001A analyzer. The average mass concentrations of organic carbon (OC) are (5.6±2.0) μg ·m^-3 in PM_1.1, (7.3±2.4) μg ·m^-3 in PM_2.1, and (12.8±4.0) μg ·m^-3 in PM_9.0; the average mass concentrations of elemental carbon (EC) are (2.3±1.4) μg ·m^-3in PM_1.1, (2.7±1.6) μg ·m^-3 in PM_2.1, and (3.4±1.7) μg ·m^-3 in PM_9.0. OC concentrations in PM_1.1 and PM_2.1 account for 43.8% and 57.0% of OC in PM_9.0, and EC concentrations in PM_1.1 and PM_2.1 account for 67.6% and 79.4%, respectively. OC and EC are enriched with fine particles. In PM_1.1 and PM_2.1, the highest concentrations of OC and EC are measured in autumn, and the lowest concentration of OC is measured in winter and EC in summer. In PM_9.0, the highest OC concentration is measured in summer. Carbonaceous aerosols are mainly composed of OC2, EC1, OC3, and OC4. In summer, the concentration of OC3 is higher than that of EC1, suggesting that biogenic sources are dominant during summer. The concentration of EC1 in winter is the highest, indicating that the impacts of motor vehicle emissions are prominent in the local area during winter. OC and EC both show bimodal distributions in four seasons, with peaks in the size ranges of 0.43-0.65 μm for fine particles and 3.3-5.8 μm for coarse particles. In PM_1.1 and PM_2.1, the sources of OC are mainly primary emissions. In PM_2.1, the highest concentration of SOC is measured in spring at (3.0±1.4) μg ·m^-3 and the lowest in winter at (1.3±1.4) μg ·m^-3, indicating that the secondary aerosol formation is significant in spring. At the Mountain Dinghu background site, OC is mainly from coal combustion and motor vehicle emissions for fine particles and from biogenic sources for coarse particles. EC is mainly from coal combustion, motor vehicle emissions, and dust.