Characterization of carbon fractions for atmospheric fine particles and nanoparticles in a highway tunnel

Fine particles (PM2.5) and nanoparticles (PM0.1) were sampled using Dichotomous sampler and MOUDI, respectively, in Xueshan Tunnel, Taiwan. Eight carbon fractions were analyzed using IMPROVE thermal-optical reflectance (TOR) method. The concentrations of different temperature carbon fractions (OC1–OC4, EC1–EC3) in both PM2.5 and PM0.1 were measured and the correlations between OC and EC were discussed. Results showed that the ratios of OC/EC were 1.26 and 0.67 for PM2.5 and PM0.1, respectively. The concentration of EC1 was found to be more abundant than other elemental carbon fractions in PM2.5, while the most abundant EC fraction in PM0.1 was found to be EC2. The variation of contributions for elemental carbon fractions was different among PM2.5 and PM0.1 samples, which was partly owing to the metal catalysts for soot oxidation. The correlations between char-EC and soot-EC showed that char-EC dominated EC in PM2.5 while soot-EC dominated EC in PM0.1. Using eight individual carbon fractions, the gasoline and diesel source profiles of PM0.1 and PM2.5 were extracted and analyzed with the positive matrix factorization (PMF) method.