The following study aims to estimate the configuration ratio of the ion compounds that identifies the cause of fine dust and ways to reduce it. In this study, the physical and chemical properties of fine particles in a tunnel and the configuration form of ionic composition were interpreted to establish reasonable measurement for air quality management. Seasonal measurements were performed by collecting samples from the Mia sageori subway station. Chemical Mass Balance (CMB) model was used to estimate the configuration ratio of ions in this study. The results showed that the test performed outside showed about 56.4% of total ion, with (NH4)2SO4, NH4NO3, CaCO3 and NaCl showing concentrations of 2.138 µg/m3, 1.957 µg/m3, 1.697 µg/m3 and 1.600 µg/m3, respectively, while the results indoor had CaCO3, NH4NO3, (NH4)2SO4 and NaCl showing concentrations of 2.272 µg/m3, 2.204 µg/m3, 1.656 µg/m3 and 1.342 µg/m3, respectively, about 65.1% of total ion. During the usage of tunnel, it was found that CaCO3, NH4NO3, (NH4)2SO4 and MgCO3 showed concentrations of 3.464 µg/m3, 1.732 µg/m3, 1.698 µg/m3 and 0.582 µg/m3, respectively, total ion of 70.2% was presented. Keywords : Carbonate carbon, Chemical mass balance (CMB), Ion compound, Subway