Spatial and seasonal distributions of carbonaceous aerosols over China

Abstract

Simultaneous measurements of atmospheric organic and elemental carbon (OC and EC) were taken during winter and summer seasons at 2003 in 14 cities in China. Daily PM₂.₅ samples were analyzed for OC and EC by the Interagency Monitoring of Protected Visual Environments (IMPROVE) thermal/optical reflectance protocol. Average PM₂.₅ OC concentrations in the 14 cities were 38.1 μg m⁻³ and 13.8 μg m⁻³ for winter and summer periods, and the corresponding EC were 9.9 μg m⁻³ and 3.6 μg m⁻³, respectively. OC and EC concentrations had summer minima and winter maxima in all the cities. Carbonaceous matter (CM), the sum of organic matter (OM = 1.6 × OC) and EC, contributed 44.2% to PM₂.₅ in winter and 38.8% in summer. OC was correlated with EC (R²: 0.56–0.99) in winter, but correlation coefficients were lower in summer (R²: 0.003–0.90). Using OC/EC enrichment factors, the primary OC, secondary OC and EC accounted for 47.5%, 31.7% and 20.8%, respectively, of total carbon in Chinese urban environments. More than two thirds of China's urban carbon is derived from directly emitted particles. Average OC/EC ratios ranged from 2.0 to 4.7 among 14 cities during winter and from 2.1 to 5.9 during summer. OC/EC ratios in this study were consistent with a possible cooling effect of carbonaceous aerosols over China.