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 that on 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, 34.93 ± 20.07 µg m–3 and 8.38 ± 4.92 µg m–3, respectively. 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 fluctuate (0.94–4.61), meaning the more efficiency in source identification. Strong correlations between OC and EC of 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, 9.59 ± 7.72 µg m–3, accounting for 42.7%, 42.3%, and 27.9% of total OC for PM0.1, PM2.5, and PM10, respectively, indicating the dominant contribution of secondary sources to OC, especially with the finer particles. The results would be significantly valuable for Vietnam’s database of atmospheric particles.