Mass Concentrations and Carbonaceous Compositions of PM0.1, PM2.5, and PM10 at Urban Locations of Hanoi, Vietnam

24-hour samples of PM0.1, PM2.5, and PM10 were collected simultaneously for the first time at a roadside site (Vinacomin) and a mixed site (HUST) in Hanoi, Vietnam, during the wet (August) and dry seasons (October to December) in 2015. High levels of PM0.1 (6.06 ± 2.71 µg m–3), PM2.5 (71.06 ± 47.52 µg m–3), and PM10 (106.47 ± 63.95 µg m–3) were observed, especially in the rice straw open burning episode. The influence of some meteorological factors and trajectories on PM0.1 concentrations was negligible compared to larger particles. The average concentrations of organic carbon (OC) and elemental carbon (EC) for PM0.1, PM2.5, and PM10 were 2.77 ± 0.98 µg m–3 and 0.63 ± 0.32 µg m–3, 23.81 ± 21.16 µg m–3 and 6.17 ± 5.87 µg m–3, and 34.93 ± 20.07 µg m–3 and 8.38 ± 4.92 µg m–3, respectively. The total carbon (TC) accounted for 59.19%, 44.65%, and 43.79% of the mass of PM0.1, PM2.5, and PM10, respectively. The OC/EC ratios ranged 3.62–5.68, in which the ratios of PM0.1 were the highest, except for those in the biomass burning period. The char-EC/soot-EC ratios widely fluctuated (0.94–4.61), meaning higher efficiency in the source identification. Strong correlations between the OC and EC in all particle sizes were found (R2 = 0.84–0.99), excluding those of PM0.1 in the dry season at Vinacomin (R2 = 0.61), implying the influence of biomass burning. The concentrations of Secondary Organic Carbon (SOC) were 1.12 ± 0.43 µg m–3, 9.49 ± 8.26 µg m–3, and 9.59 ± 7.72 µg m–3, accounting for 42.7%, 42.3%, and 27.9% of the total OC for PM0.1, PM2.5, and PM10, respectively, indicating the dominant contribution of secondary sources to OC, especially in the finer particles. These results are highly valuable to Vietnam’s database of atmospheric particles.