Characteristics of elemental carbon and organic carbon in PM10 during spring and autumn in Chongqing,China

PM10 (particulate matter with aerodynamic diameter less than 10 m) samples were collected simultaneously at nine urban sites and one urbanbackground site during two intensive observation campaigns in 2006. Concentrations of elemental carbon (EC) and organic carbon (OC) in PM10were analyzed using an element analyzer. The characteristics regarding spatial and seasonal distribution patterns of OC and EC concentrations andtheir contributions to PM10 mass, as well as correlation between OC and EC, were investigated in detail. The average OC and EC concentrationsfor urban sites were 57.5 ± 20.8 and 8.3 ± 3.9 g/m3, respectively, both being around three times higher than those for urban background site. As awhole, EC concentrations did not show distinct seasonal variations, though OC concentrations were generally higher in autumn than in spring. Forurban sites, total carbonaceous aerosol (TCA) accounted for 33.2% in spring and 35.0% in autumn of PM10 mass. The OC and EC concentrationswere found significantly correlated to each other both in spring and in autumn, implying the existence of similar emission sources such as coalcombustion. The OC/EC ratios generally exceeded 2.0, indicating the presence of secondary organic carbon (SOC), whose estimated concentrationfor urban Chongqing was 26.7 and 39.4 g/m3, accounting for 48.9 and 61.9% of the total OC observed in the samples, in spring and in autumn,respectively.