Status of PM in Seoul metropolitan subway cabins and effectiveness of subway cabin air purifier (SCAP)

The increasing importance of indoor air quality management on public transport led the Korean government to amend the indoor air quality control in public use facilities, etc. Act including modes of public transport under the Act from June 2013. Particulate matter (PM) in subway systems is reported as being mostly generated by friction—between the wheels and the rails, between the wheels and the brake pads, and between the catenaries and the pantographs. In order to reduce PM level in subway cabins, a newly developed subway cabin air purifier (SCAP) was installed on the ceilings of the cabins. In this study, we analyzed indoor PM concentrations through continuous measurement of PMs less than 10 μm in diameter (PM₁₀) and PMs less than 2.5 μm in diameter (PM_2.5) in the cabins of line 2 and line 5 of the Seoul metropolitan subway network, comparing the concentrations in cabins where SCAP devices were installed to cabins without them in order to verify SCAP effectiveness. In both cabins with and without SCAP, the ratio of indoor to outdoor PM₁₀ (I/O for PM₁₀) showed a two-times higher value in line 5 than in line 2, which indicated that the entirely underground line 5 was less ventilated with outdoor air. In addition, the ratio of indoor PM_2.5/PM₁₀ showed that coarse mode PM was more abundant in line 5 due to poor ventilation in the tunnel sections compared to that of line 2. Regarding the effectiveness of SCAP, it was found that changes of PM₁₀ concentrations in line 2 and line 5 were from 132.8 to 112.2 μg/m³ (15.5 % efficiency) and from 154.4 to 114.2 μg/m³ (26.0 % efficiency) after SCAP installation, respectively.