Size distribution characteristics of carbonaceous aerosol in a rural location in northwestern China

Size-segregated aerosol samples were collected in Dunhuang, China during 2012. The carbonaceous aerosols were quantified with the thermal/optical reflectance (TOR) method. In this study, two modes were observed in the size distribution of respective carbonaceous components. The first mode was the fine particle mode, and the second mode was in the coarse size range. OC, OP, and char showed a bimodal size distribution, with the fine particles as the major fraction in summer, autumn, and winter. Each of these components exhibited a similar seasonal pattern with the highest concentrations in winter and the lowest concentrations in summer. The highest soot (EC2+ 3, sum of EC2 and EC3) concentrations were in spring and the lowest concentrations were in fall, both in the fine and coarse modes. The correlations between different carbon fractions in size-segregated aerosol samples are discussed. OC and EC in Dunhuang are derived from coal combustion, biomass burning, and motor exhaust. The highest values of char/soot occurred in autumn, and lower values were found in the winter due to increased coal combustion.