Characteristics and Source Apportionment of Carbon Components in Road Dust PM2.5 and PM10 During Spring in Tianjin Derived by Using the Quadrat Sampling Method

Abstract

In order to study the characteristics and sources of carbon fractions in PM2.5 and PM10 of road dust in Tianjin, samples of road dust were collected by the quadrat sampling method in April 2015 in Tianjin, and samples were re-suspended on filters by using a NK-ZXF sampler. A Thermal Optical Carbon Analyzer (IMPROVE-TOR) was employed to measure the concentrations of organic carbon (OC) and elemental carbon (EC), and the pollution characteristics and sources were investigated by non-parametric tests and OC/EC ratio, correlation, and cluster analyses. The results showed that ω(total carbon, TC) in PM2.5 of road dust amounted to 4.89% (secondary road) -18.83% (expressway), ω(OC) amounted to 3.57% (secondary road) -15.39% (expressway), and ω(EC) amounted to 1.32% (secondary road) -3.44% (expressway); meanwhile, ω(TC) in PM10 of road dust was 8.14% (secondary road) -19.71% (expressway), ω(OC) was 5.91% (secondary road) -16.28% (expressway), and ω(EC) was 1.96% (main road) -3.43% (expressway). The mass fraction of each carbon component for the expressway was relatively high, and that for the secondary trunk road was relatively low, which may have been due to the large traffic volume on the expressway and corresponding large amounts of exhaust emissions from motor vehicles, whereas there were fewer vehicles on the secondary trunk road. Additionally, ω(OC) was significantly larger than ω(EC) for all types of roads, and ω(EC) did not vary much among the different road types. The non-parametric tests of two related samples showed that there was no significant difference in the mass fraction of each carbon component between PM2.5 and PM10. The correlation analysis showed that the sources of OC and EC in road dust were roughly the same. The OC/EC ratio analysis and cluster analysis showed that the main sources of the carbon components in the dust of roads in Tianjin in spring were coal combustion, motor vehicle exhaust, and biomass burning.