Yuhong Guo

Mass concentrations of organic carbon (OC) and elemental carbon (EC) in size-resolved aerosols were investigated at four sites (three cities and one country) in the Beijing-Tianjin-Hebei region from September 2009 to August 2011. The size distributions of OC and EC presented large evolutions among rural and urban sites, and among four seasons, with highest peaks of OC and EC in fine mode in urban areas during winter. Geometric mean diameters (GMDs) of OC and EC in fine particles at urban sites during winter were lower than those at rural site mainly due to effects of fine particle coagulation and organic compound repartitioning. Fossil fuel emissions were a dominant source of OC and EC in urban areas, while biomass burning was a major source of OC and EC at rural site. Trajectory clustering and CWT analysis showed that regional transport was an important contributor to OC and EC in Beijing.

In 2012, size-segregated aerosol samples were collected in Xishuangbanna, a forest station in southwest China. The concentrations of organic and elemental carbon (OC and EC for short) were quantified with thermal/optical carbon analyzer in the filter samples. OC and EC exhibited similar seasonal patterns, with the highest concentrations in spring, possibly due to the influence of biomass burning in south and southeast Asia. The mass size distributions of OC and EC were bimodal in all the sampling seasons, each with a dominant peak in the fine mode of 0.4–0.7 μm and a coarse peak in the size range of 2.1–4.7 μm. In fine mode, OC and EC showed smaller geometric mean diameters (GMDs) during winter. OC and EC were prone to be more concentrated in fine particles in spring and winter than in summer and autumn. Furthermore, EC was more abundant in fine particles than OC. Good correlations (R ² = 0.75–0.82) between OC and EC indicated that they had common dominant sources of combustion such as biomass burning and fossil fuel combustion emissions. The daily average OC/EC ratios ranged from 2.1 to 9.1, more elevated OC/EC ratios being found in the winter.

The organic carbon (OC) and elemental carbon (EC) collected by eight-stage air samplers over northern China during spring 2012 were determined to characterize the spatial variations, size distributions, and sources of carbonaceous aerosols. OC and EC had high concentration levels and spatial heterogeneity. Higher carbonaceous aerosol loadings were found in urban areas, and high concentrations of OC and EC were found in eastern parts of northern China, including Beijing, Taiyuan in Shanxi Province, Yucheng in Shandong Province, Xianghe in Hebei Province, and Shenyang in Liaoning Province. Except the Cele site, OC and EC at all the sites showed a bimodal distribution, peaking in the size of 0.4–0.7 and 4.7–5.8 μm. Carbonaceous aerosols in the fine mode in the urban areas are mostly presented in smaller sizes than those in the rural/regional background areas. For most sites, mass median aerodynamic diameter (MMAD) values in the fine particles for OC were higher than those for EC with the addition of semi-volatile organics. Good correlations between OC and EC in all the cities (5 in North China and 1 in northeast China) may suggest the impact of anthropogenic emissions on carbonaceous aerosols in the above regions.