14To enhance the health of subway users, it is essential to investigate the generation, resuspension, and decay of 15 particles in an underground tunnel. In this paper, we analyzed the diurnal pattern of variation in particle 16 concentration in a subway tunnel. The mass concentration of particles was measured in a shelter located halfway in 17 the underground tunnel connecting Janghanpyeong station and Gunja station on Seoul Subway Line 5 by using an 18 aerodynamic particle sizer, a dust monitor, and a fast mobility particle sizer. The particle mass concentration 19 increased uniformly as a train passed through the tunnel, which was followed by an exponential decay. The particle 20 concentration in the tunnel decreased when the decrease of the number of particles between train operations 21 exceeded the number of particles generated and resuspended by a passing train, and increased in the opposite case. 22The diurnal variation of particle concentration in the tunnel according to train operation could be predicted by using 23 such a pattern of variation in the mass concentration of particles. 24 25

No abstract

In megacities, a subway system is a powerful means of public transportation, carrying people every day. Due to wear of train wheels and rails, dust is heavily generated and dispersed in tunnels and platforms. For the improvement of air quality in subway tunnels, a non-powered dust removal device consisting of two inertial separators, such as a louver and baffle, was designed. This device can be installed underneath the train cabin to remove dust as soon as it is generated. Prior to design of the device, distributions of airflow velocity and dust concentration underneath the train cabin during the operation of the subway train were investigated. Average airflow velocity was found to be approximately 26% of train speed during the cruising period. The fractional dust removal efficiency and pressure drop of the lab-scale dust removal device were tested in a wind tunnel. Removal efficiency of particles smaller than 10 μm is approximately 60% at 4 m/s.

In underground tunnels, friction between the wheels and rails of subway trains creates particles, which are spread by the wind generated when trains pass by. A louver dust collector was attached to the bottom of a T-car of Seoul Subway Line 5 train in an effort to remove PM 10 inside tunnels, and obtain data when it was in actual operation. It made several round trips during which differential pressure of the louver dust collector was measured in relation to train speed. By comparing and verifying the differential pressure estimated by simulation and that actually measured, it was possible to estimate average flow of air that went into the louver dust collector. Furthermore, by comparing and verifying the measurement results on collection efficiency of a lab-scale louver dust collector in a wind tunnel, along with the results of numerical analysis, it was possible to estimate the collection efficiency in relation to subway train speed. As a result, it was confirmed that higher running speeds of subway trains increased the flow of air going into the louver dust collector and subsequently decreased the particle size corresponding to 50% collection efficiency. In other words, the cut-off size was estimated to be 9.7 µm at the lowest speed of 5 km h -1 , and 4.9 µm at the top speed of 65 km h -1 , in normal speed range for the Seoul Subway Line 5 trains.