地铁轨道交通作为一个人工封闭的环境，建在地面层以下(地面线、高架线除外

As an artificially enclosed environment, subway rail transit is built below the ground level (except for ground lines and overhead lines), and is basically isolated from the outside air. Indoor air can only rely on station entrances and exits, ventilation shafts above train tunnels, tunnel openings and the outdoor environment Connected. Due to the economic cost of operation, the various ventilation and air-conditioning equipment in the station can only be maintained at a stable level. These characteristics limit the relatively poor sanitary environment in most subway stations. With the <br>increase of passenger flow during subway operation time , pollution sources in the subway increase, resulting in insufficient natural ventilation, which is not conducive to the dilution and elimination of pollutants. At the same time, the underground space lacks the characteristics of sunlight, high density of people, and strong mobility. It is easy to cause the spread of disease; when people are in a crowded environment with poor air circulation, they often produce irritability and depression, which is not conducive to physical and mental health; subway trains run short, and passengers stay in the station for a short time and flow It is highly sensitive, so the sensitivity to the temperature and humidity in the car is relatively high, and the sensitivity to the air quality is relatively low. The operating characteristics of the subway result in the design of the ventilation and air-conditioning system of subway trains, often only considering the requirements of temperature and humidity, while ignoring the influencing factors of air quality, and failing to take appropriate measures to control. However, inhalable particulate matter will accumulate for a long time and is not easy to dissipate. It may accumulate to a higher concentration in a closed underground space, which <br>will inevitably threaten the health of passengers and staff. Lack of natural light, most subways are completely underground. Except for the natural light at the entrance and exit, the interior of the station generally lacks natural light; to a certain extent, subway trains can be regarded as "moving buildings" and should be treated as platforms And the air quality in the compartment should be paid enough attention, otherwise it is very likely that a problem similar to the sick building syndrome will occur [4].

As an artificially enclosed environment, subway rail transit is built below the ground floor (except ground line and elevated line), which is basically isolated from the outside air, which can only be connected with the outdoor environment by the station entrance and exit, the ventilation shaft at the top of the train tunnel, and the tunnel entrance. Due to the economic cost of operation, the various types of ventilation and air-conditioning equipment in the station can only be maintained at a stable level, which limits the relatively poor sanitation environment in most subway stations. Passenger traffic as the subway runs<br>Increased, the subway pollution source increased, resulting in the original lack of natural ventilation, is not conducive to the dilution and elimination of pollutants, while the underground space lack of sunlight, personnel density, strong mobility characteristics, easy to cause the spread of disease; The sensitivity to air quality is relatively low. The operating characteristics of the subway lead to the design of the subway train ventilation and air conditioning system, often only consider the temperature, humidity requirements, while ignoring the impact of air quality factors, did not take appropriate measures to control. However, inhalable particulate matter can accumulate over a long period of time and may accumulate to higher concentrations in enclosed underground spaces.<br>It is bound to pose a serious threat to the health of passengers and staff. Lack of natural light, the vast majority of subways are completely underground, in addition to the import and export of natural light exposure, the station generally lack of natural light;

As an artificial closed environment, metro rail transit is built below the ground level (except for ground line and elevated line), which is basically isolated from the outside air. Indoor air can only be connected to the outdoor environment by the station entrance and exit, the ventilation shaft above the train tunnel and the tunnel entrance. Considering the economic cost of operation, all kinds of ventilation and air conditioning equipment in the station can only be maintained at a stable level, which limits the relatively poor sanitary environment in most subway stations. With the time of metro operation, passenger flow<br>In addition, the underground space is lack of sunlight, high density of personnel and strong mobility, which is easy to cause the spread of diseases. When people are in a crowded environment and the air flow is not smooth, people will often produce irritable and depressed mood, which is not conducive to physical and mental health; Because of the short running interval, short stay time and high mobility, the subway train has high sensitivity to the temperature and humidity in the train, and has low sensitivity to air quality. Due to the operation characteristics of subway, when designing the ventilation and air conditioning system of metro train, the requirements of temperature and humidity are often considered, while the influencing factors of air quality are ignored, and appropriate measures are not taken for control. However, the inhalable particles will accumulate for a long time and will not be easily dissipated, and may accumulate to a higher concentration level in the closed underground space,<br>It will seriously threaten the health of passengers and staff. Due to the lack of natural light, most subways are completely underground. In addition to the entrance and exit, there is a general lack of natural light inside the station. To a certain extent, the subway train can be regarded as a "moving building", so we should pay enough attention to the air quality in the platform and carriage, otherwise it is very likely to have problems similar to sick building syndrome [4] 。<br>