A review of traditional and advanced technologies for the removal of particulate matter in subway systems

Abstract

The pollution status of particulate matter (PM) in a subway system and technological trends in their reduction were discussed in this study. The levels of PM2.5 and PM10 are generally found to be higher in the underground platforms and tunnels than those in the outdoor air. It has also been reported that the composition of fine dust in the subway consists of various substances including heavy metals (like Fe), carbonaceous matter, and solvent extractable organic matter (SEOM). It was confirmed that subway dust was created mainly by wearing on wheels, rails, and brakes. In addition, the concentration of PM in such environment was influenced not only by internal factors (eg, operating conditions of trains and ventilation systems, number of passengers, and the structure of subway stations) but also by outside factors (eg, ambient air concentration). Up to now, various techniques (ventilation fans, platform screen doors (PSDs), magnetic filters, small jet fans, artificial intelligent ventilation systems, hybrid filters, etc) have been studied to reduce PM in underground subway systems. In this study, we reviewed the air quality of major subway stations with the focus on PM and relevant technologies for its reduction.

Environmental and Health Effects of Ventilation in Subway Stations: A Literature Review

“…Applying liquid dust suppressants to new ballasts, prohibiting diesel-powered trains or facilities, building along a straight, horizontal trajectory, designing a variable longitudinal profile railway, and slowing trains at sharp curves and high gradients may minimize wears of rail, wheels, and brakes, and then reduce metallic PM emissions. Besides, developments of materials that emit fewer and less toxic particles are a positive way forward [5,82,[233][234][235][236]. When it comes to VOCs, controlling ground fossil-fueled vehicles effectively decreases the VOC concentrations in subways [177], and restricted use and prompt cleaning of spilled oils, solvents, deodorants, and decoration materials can reduce indoor sources.…”

Current Status, Challenges and Resilient Response to Air Pollution in Urban Subway

“…Influenced by the local environment and the ground environment, the concentration of subway PM in some areas is higher in autumn and winter when the ground air pollution is more serious, and the microbial content in subway stations is significantly increased in the local florescence [32]. In addition, train operating age [17], brake type [13], and environmental control system [18,47] will also directly or indirectly affect the concentration of PM.…”

“…We simplify the problem to consider only the construction cost of installing screen doors and air-conditioning systems in substandard stations, while ignoring other costs, such as shadow costs of passenger flows, equipment operating costs, and the cost of installing other technologies, such as exchanging rails and wheels, installing iron particle captures, washing walls of tunnels, and wearing masks. There are at least 4 reasons why this paper suggests to choose installing screen door and air-conditioning systems over other technologies: compared to other methods, installing screen door systems are effective, more convenient, mature in technology, and operational in terms of cost [13]. The method that exchanges or upgrades materials of rails and wheels, and the technology that installs iron particle captures are still under R&D process and its cost and mitigation effectiveness is still unknown.…”

“…Individual Subway System Potential Cost = Regional Total Cost/Number of Cities (13) In Asia, for example, there are about 2588 underground stations, 7218 km of subway mileage, and 70 cities counted. Assuming that all stations are equipped with screen door systems, the average cost per city is about USD 151 million:…”

“…In terms of the site characteristics, the concentration of PM on the ground floor is lower than that on the underground floor, and the concentration on the platform is higher than that in the train compartment. The highest concentration of PM is found on the underground platform and the lowest concentration in the ground train compartment due to the combined action of adverse factors [10][11][12][13]. In terms of time, the variation of PM concentration is related to trains frequency [11,14], seasons [15], and so on [16], as well as other matters which directly or indirectly affect the PM concentration such as the train running age [17], brake types [13], and environmental control systems [18].…”