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To protect the health of subway users, it is essential to investigate the generation, resuspension, and decay of particles in underground tunnels. In this paper, we analyzed the diurnal pattern of variation in particle concentration in a subway tunnel. The mass concentration of particles was measured in a shelter located midway in the underground tunnel connecting Janghanpyeong station and Gunja station on Seoul Subway Line 5 by using an aerodynamic particle sizer, a dust monitor, and a fast mobility particle sizer. The particle mass concentration increased uniformly as a train passed through the tunnel, which was followed by an exponential decay. The particle concentration in the tunnel decreased when the decrease in the number of particles between train operations exceeded the number of particles generated and resuspended by a passing train, and increased in the opposite case. The diurnal variation in particle concentration in the tunnel according to train operations can be predicted by applying such a pattern of variation to the mass concentration of particles.

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 PM10 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.