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A hybrid dust collector attached to a subway train bottom was developed for the effective removal of subway particulate matter (PM), by considering the fluctuating speed of a subway train between stations. It combines an electrostatic precipitator, which has good collection efficiency when the flow velocity is low, and an inertial dust separator, which has good collection efficiency when the flow velocity is high. The electrostatic precipitator and inertial dust separator guarantee a high collection efficiency regardless of the subway train operating speed by compensating for the other's shortcomings. Wind tunnel test and numerical simulation were conducted to verify the performance of the hybrid dust collector. The experiment and simulation results were compared to verify the prediction accuracy of the simulation method. The collection efficiencies of the electrostatic precipitator and inertial dust separator were then simulated for various operating speeds of the subway train to predict the overall collection efficiency of the hybrid dust collector. As a result, when airflow velocity at the hybrid dust collector inlet varied from 2 to 8 m/s, subway PM10 or PM2.5 collection rate of a single hybrid dust collector was predicted to be in the range 88 ∼ 123 μg/s or 30 ∼ 35 μg/s, respectively. The use of multiple such hybrid dust collectors attached to the subway train bottom is expected to be effective in reducing fine dust concentration in subway tunnels. Copyright © 2019 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

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 (PM) and PMs less than 2.5 μm in diameter (PM) 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 PM (I/O for PM) 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/PM 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 PM concentrations in line 2 and line 5 were from 132.8 to 112.2 μg/m (15.5 % efficiency) and from 154.4 to 114.2 μg/m (26.0 % efficiency) after SCAP installation, respectively. [ABSTRACT FROM AUTHOR]

Understanding characteristics of diurnal particle concentration variation in an underground subway tunnel is important to reduce subway passengers' exposure to high levels of toxic particle pollution. In this study, real-time particle monitoring for eight consecutive days was done at a shelter located in the middle of a one-way underground subway tunnel in Seoul, Republic of Korea, during the summer of 2015. Particle mass concentration was measured using a dust monitor and particle number concentration using an optical particle counter. From the diurnal variations in PM10, PM2.5, and PM1, concentrations of particles larger than 0.54 μm optical particle diameter were affected by train frequency whereas those of particles smaller than 0.54 μm optical particle diameter were not changed by train frequency. Number concentration of particles smaller than 1.15 μm optical particle diameter was dependent on outdoor ambient air particle concentration level, whereas that of particles larger than 1.15 μm optical particle diameter was independent of outdoor ambient air due to low ventilation system transmission efficiency of micrometer-sized particles. In addition, an equation was suggested to predict the diurnal particle concentration in an underground tunnel by considering emission, ventilation, and deposition effects. [ABSTRACT FROM AUTHOR]

As the number of people using rapid transit systems (subways) continues to rise in major cities worldwide, increasing attention has been given to the indoor air quality of underground stations. This study intended to observe the change of PM distribution by size in an underground station with PSDs installed located near the main road in downtown Seoul, as well as to examine causes for the changes. The results indicate that the PM suspended in the tunnel flowed into the platform area even in a subway station where the effect of train-induced wind is blocked by installed PSDs, as this flow occurred when the PSDs were opened. The results also indicate that coarse mode particles generated by mechanical friction in the tunnel, such as that between wheels and rail, also flowed into the platform area. The PM either settled or was re-suspended according to size and whether the ventilation in the platform area was in operation or if the platform floor had been washed. The ventilation system was more effective in removing PM of smaller sizes (fine particles) while the wash-out performed after train operations had stopped reduced the suspension of coarse mode particles the next morning. Despite installation of the completely sealed PSDs, inflow of coarse mode particles from the tunnel seems unavoidable, indicating the need for measures to decrease the PM generated there to lower subway user exposure since those particles cannot be reduced by mechanical ventilation alone. This research implicate that coarse PM containing heavy metals (generated from tunnel side) proliferated especially during rush hours, during which it is very important to control those PM in order to reduce subway user exposure to this hazardous PM. [ABSTRACT FROM AUTHOR]