轨道交通列车内空气质量研究现状与展望

城市轨道交通因其运量大、效率高、能耗低等诸多优点，成为城市公共交通的主要方式，其中主要以地铁为主。虽然通勤者在地铁内停留时间短，但因列车及乘客的活动，其内自然通风不足，空气质量差，影响出行人员身体健康。研究表明：颗粒物（PM）、挥发性有机物（VOCs）和细菌是主要的空气污染物。其中，轨道交通颗粒物主要来源于列车与轨道之间的磨损，且颗粒物中金属元素含量丰富，遗传毒性较强。VOCs主要来源于地铁装饰物的挥发，细菌与真菌等主要受客流量、通风、温度等因素影响。此外，文章综合叙述了暴露于PM以外的各种空气污染物的健康风险。最后，指出进一步优化列车运行条件、开发先进的空气净化装置，是未来轨道列车空气质量研究与控制的方向。

Air quality standard and pollution of railway transit system

Background, aim, and scope Urban rail transit which is mainly based on subway is the main mode of urban public transportation because of its advantages, such as large volume, high efficiency and low energy consumption. Due to the activities of trains and passengers, although passengers stay in subway for a short time, the insufficient natural ventilation and poor air quality affects the health of commuters. What is more, many studies indicated that particulate matter (PM), volatile organic compounds (VOCs) and bacteria in the air were the main air pollutions. In order to summarize the research and related standards of air quality in railway transit system in various countries and regions, this paper is written. This paper summarizes the air quality of railway transit system, relevant laws and regulations, control measures, and puts forward the prospect. Materials and methods This review summarized detailedly the air quality standard, pollutant concentration levels, types of chemical substances, related sources and health risk assessment of railway transit (mainly subway). Results Among them, particles in rail transit mainly come from the wear and tear between trains and tracks. Studies have found that the concentration of rail train system is higher than the level of atmospheric environment, the exposure level of underground transportation system is also higher than that of surface transportation system, and the PM concentration level of subway platform is significantly higher than that of subway too. More importantly, the content of metal elements in the air of subway is rich and the genetic toxicity of them is strong. Studies have shown that the concentration and chemical composition of rail transit particles depend on many factors, such as outdoor air quality, differences in the depth and design of stations and tunnels, composition of wheel, track, brake pad and power supply materials. Furthermore, VOCs mainly come from the volatilization of subway decorations, whose exposure level is lower than that of road transportation, posing a carcinogenic risk to human body. CO₂ is mainly related to high passenger rate. Bacteria and fungi are mainly affected by passenger flow, ventilation, temperature and other factors. Discussion This paper analyzed the air quality guidelines of other countries which have reference significance for the establishment of air standards of railway carriages in China. Studies have shown that the concentration and chemical composition of rail transit particles depend on many factors, such as: outdoor air quality, differences in the depth and design of stations and tunnels, composition of wheel, track, brake pad and power supply materials, etc. Most studies have found higher levels of PM pollution in metro systems compared to outdoor ambient air. There were also significant differences in the levels of particulate matter in the platforms and carriages of subway systems. In subway PM samples, metal content was high, and commuters were exposed to a large amount of toxic metals during their commute. It is worth noting that subway particles contain a large number of metal elements, which cause greater damage to human health. Besides, the concentration of toluene and benzene in VOCs of urban rail transit is both high. The concentration difference among these studies is caused by different factors such as subway train running time, number of passengers, driving conditions and urban pollution level. Commuters exposed to VOCs in subway cars may cause perceived health problems and risks, and have a negative impact on health. Studies have found that formaldehyde inhalation can aggravate asthma symptoms, and benzene is a carcinogenic compound, which is closely related to the induction of leukemia. VOCs is commonly evaluated for human health risk as carcinogenic risk (LCR). However, CO₂ mainly comes from the breath of passengers, and the number of passengers and activity level are directly related to it. There is no CO source in the train, only the environmental concentration can affect the concentration in the train. Exposure to airborne microorganisms is often associated with adverse health effects, and bacteria are often considered the pathogens of infectious diseases. Conclusions The research on rail train air quality mainly focuses on subway system, including PM and VOCs. Recommendations and perspectives What is more, this paper states that the development direction of rail transit system is to optimize the air conditioning system, tires and brake devices, braking mode and filtration system. Additionally, advanced air purification devices are also necessary to improve air quality in subway stations. However, the development of effective and active countermeasures requires further study of particle characteristics, generation mechanism and exposure factors.