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As urban rail transit networks continue to expand, air quality in metro tunnels has received increasing attention from operators and passengers. Unlike ordinary buildings, metro tunnels are relatively enclosed underground spaces. Train operation, braking friction, passenger activity, and outdoor air intake can all introduce particulate matter and other pollutants. Therefore, relying solely on traditional ventilation may no longer be sufficient for refined air quality management. Developing an effective metro tunnel air purification solution has become an important way to improve the underground transportation environment.
Do Metro Tunnels Need Air Purification?Metro trains operate frequently and at relatively high speeds. Friction between wheels, rails, braking systems, and power supply components can generate dust and metal particles. Some fine particles may enter platforms and other underground areas along with air movement. Studies have found that particulate matter in underground metro environments can come not only from outdoor air but also from train operation and the resulting wear and resuspension of particles.
Metro tunnels are generally long and relatively enclosed, while air exchange is affected by the tunnel structure, train movement, and ventilation system operating conditions. During periods of high passenger flow or frequent train operation, insufficient ventilation and purification capacity may cause particulate matter to accumulate temporarily.
Therefore, a metro tunnel air purification solution should not focus only on the filtration efficiency of individual equipment. Instead, it should be designed in combination with the overall ventilation system.
A well-designed metro tunnel air purification system normally uses the ventilation system as its foundation. Fans, air ducts, dampers, and other components are used to organize airflow, while appropriate purification equipment is added according to the characteristics of the pollutants.
The ventilation system is mainly responsible for air circulation and pollutant dilution, while air purification equipment focuses on removing particulate matter from the air. Combining the two can reduce the need to simply increase air exchange rates, helping to control energy consumption while improving air quality.
For PM2.5, PM10, and other suspended particles, appropriate technologies can be selected according to tunnel airflow, pollutant concentration, and available installation space. Possible solutions include filtration and electrostatic precipitation. Electrostatic precipitators charge particles and then use an electric field to collect them, separating particulate matter from the airflow.
For large metro tunnels, it is also important to consider pressure drop, air handling capacity, operating stability, and maintenance requirements. Excessive resistance from purification equipment should be avoided because it can affect the performance and energy consumption of the existing ventilation system.
Not every area of a metro system requires exactly the same air purification configuration. Actual projects should be designed according to pollution sources, space size, passenger density, and the length of time people stay in each area.
Area | Main Air Quality Issues | Recommended Measures | Key Considerations |
Metro Tunnel | Dust, PM2.5, metal particles | Ventilation + air purification | High airflow, low pressure drop |
Platform | Particulate matter, passenger activity | Fresh air + filtration | Passenger comfort |
Concourse | Outdoor air and passenger-generated particles | Fresh air system + filtration | Air exchange efficiency |
Equipment Room | Dust affecting equipment | Filtration + regular maintenance | Equipment protection |
Long-Distance Tunnel | Limited air exchange | Zonal ventilation + purification | System stability |
The tunnel is one of the key areas for air purification. Equipment configuration should be determined according to tunnel length, cross-sectional area, train frequency, and air quality monitoring data. For areas where pollutant concentrations fluctuate significantly, online monitoring equipment can also be integrated into the system. This allows fans and purification equipment to adjust their operating levels according to real-time air quality conditions.
Platforms and concourses are high-occupancy areas. In addition to controlling particulate matter, the ventilation system needs to consider fresh air volume, temperature, humidity, and airflow distribution.
In practical operation, increasing outdoor air circulation, strengthening ventilation system cleaning and maintenance, and improving filter replacement frequency can all help reduce PM2.5 and PM10 levels. Taipei Metro has also implemented measures such as increasing outdoor air circulation, strengthening ventilation system cleaning and maintenance, and increasing filter replacement frequency to improve air quality.
The processing capacity of air purification equipment needs to match the airflow requirements of the tunnel ventilation system. If the equipment capacity is too low, the actual purification effect may be limited. If the pressure drop is too high, fan energy consumption may increase.
Therefore, the design stage should comprehensively consider airflow, air velocity, equipment resistance, purification efficiency, and operating conditions.
PM2.5, PM10, and other air quality sensors can provide real-time information about air conditions in tunnels and stations. When pollutant concentrations increase, the system can increase ventilation and purification capacity in the relevant areas. When air quality is good, the operating intensity can be reduced to avoid unnecessary energy consumption.
This intelligent control approach can help improve both system efficiency and long-term operating performance.
A metro air purification system cannot simply be installed and left to operate without regular maintenance. Filters, dust collection components, fans, and air ducts all require periodic inspection and servicing.
In tunnel environments with relatively high dust loads, timely cleaning and replacement of relevant components are particularly important. Regular maintenance helps maintain stable purification performance and reduces the risk of system efficiency declining over time.
In the ventilation systems used for metro tunnels and other underground engineering projects, flexible ventilation ducts are also important components for air delivery. PVC-coated fabrics generally offer good mechanical strength, water resistance, and weather resistance. They can be manufactured into ventilation ducts, air tubes, and ventilation sleeves in different sizes according to project requirements.
For projects requiring long-distance air delivery, temporary ventilation, or ventilation in complex construction environments, selecting suitable PVC ventilation duct materials can help optimize airflow routes and improve the adaptability of the ventilation system.
During actual application, factors such as required airflow, air pressure, duct diameter, connection method, installation environment, and project conditions should be considered when selecting suitable ventilation materials and structures.
A complete metro tunnel air purification solution should consider the entire process, from pollution source analysis and ventilation organization to purification equipment, air quality monitoring, and long-term maintenance. Instead of focusing only on the purification efficiency of a single piece of equipment, the overall system should be designed according to actual project requirements.
By combining ventilation systems + air purification equipment + online monitoring + regular maintenance, particulate pollution in tunnels and underground spaces can be managed more systematically. At the same time, zonal design based on the requirements of different areas can help balance air quality, energy consumption, and maintenance costs.
For metro construction, tunnel engineering, and underground ventilation projects, selecting reliable ventilation materials and supporting equipment, together with customized system design based on actual operating conditions, provides an important foundation for creating a stable and effective long-term air quality control system.
