Investigation Of Airborne Particle Concentrations (Pm2.5) In The Longest Subway Line In Tehran In Winter

in many metropolitan cities of the world due to its high capacity of passenger transportation, speed and safetyHowever, the high density of particulate matter in the air of underground subway platforms and the negative impact of these particles on human health has attracted much attention If the indoor air quality in the metro system is not managed properly, metro passengers and employees will be exposed to air pollutants in this environmentParticle Materials have been selected by the US Environmental Protection Agency as one of the six major pollutant indicators. PM2.5 is a particulate matter (PM) less than 2.5 μg/m3, which through inhalation may penetrate the lungs, alveoli, and blood vessels, causing respiratory and cardiovascular disease and even premature death] In the short exposure term, increasing every 10 g / m3 with a PM2.5 concentration increases the mortality from respiratory and cardiovascular diseases by 0.38% . Although it may seem that travelers spend little time in the subway system, however, exposure to high concentrations of PM can adversely affect their health]. Also, due to the large number of passengers, contact with air pollution in this place is of great health importance.In this cross-sectional (descriptive-analytical) study, the concentration of PM2.5 suspended particles on station platforms, inside ticket offices, outside stations and inside the Tehran Metro Line 1(one of the busiest metro lines in Tehran) In winter, it was measured for a month between 6 am and 2 pm (one shift). This line has 29 stations with a length of 39 km. And approximately 2 million passengers travel on the platforms of this line daily .Tehran metro ventilation system is cold ventilation, which is used only in spring and summer. In winter, the outside air is distributed in the stations without filtering and proper ventilation. In the warm seasons of the year (summer, spring), the wetting process by water ponds is used to filter the air, but in the cold seasons of the year (autumn, winter), the wetting ponds are deactivated. And only air conditioning is done.To measure the concentration of PM2.5 suspended particles, a portable direct reading suspended particle measuring device called HAZ DUST model 5000 EPMA was used and the particle measurement method was performed according to OSHA CIM instructions.
In this method, air is drawn by a vacuum pump through a membrane filter with a diameter of 47 mm and the concentration of dust particles per second is detected. Sampling flow was 4 liters per minute, working temperature (The temperature at which the device can measure correctly (was -10 to 50 ° C, humidity was 95% and storage temperature) The temperature at which the device must be maintained to remain calibrated (was 20 ° C to 60 ° CAccording to the results of this study, the mean and standard deviation of passenger population in stations was 1292.33 ±1072.64 ،, the average temperature of stations was 14.73± 2.73 ° C, the average temperature of wagons was 27.34 ±1.34 ° C, the average humidity of stations was 21.64 ±3.13 % and the average humidity of the station was 61.24 ±1. 5 %.
Among the studied stations, the highest average concentrations of PM2.5 particles in the platform and ticket office of Tajrish station were 0.034 ± 0.016 mg/m3 and 0.025 ± 0.024 mg/m3, respectively (Figure 1). The location of this station (the presence of the shrine of Imam Zadeh Saleh, and Tajrish Bazaar), increases the passenger density, as well as the increase in car traffic in the streets outside the station increases the entry of pollutants into the station. Tehran Metro ventilation system is a cold ventilation system. Ponds are used to trap pollutants and according to observations, there is no filter, so in winter, due to the decrease in temperature, the natural ventilation system is not used and due to the lack of proper ventilation system, it causes outside air to enter. Without filtration, it enters the station, which increases the concentration of particles in the subway environment, and this factor can increase the concentration of particles in Tajrish station.The highest average concentration of PM2.5 particles at the subway entrance is related to the south terminal station with 0.023 ±0.006 mg/m3. High density of vehicles (passenger buses and private cars) and high population density (due to the presence of the southern passenger terminal) are the factors affecting the increase of particle concentration outside this station (Table 2). According to Tukey post hoc test, the mean concentration of PM2.5 particles on the platform at Saadi station with Shahreri and the southern terminal, Tajrish with Shahreri and the southern terminal, was significantly different. (P <0.001) The mean concentration of PM2.5 particles in the ticket office of Tajrish station was significantly different from Shahreri, Khayyam and Saadi. (001/0> P). The mean concentration of PM2.5 particles at the entrance of the south terminal station was significantly different from other stations. (P <001/0).Also, the concentration of PM2.5 particles in both ground and underground states of stations in different measurement positions (on platforms, ticket halls and outside stations) are significantly different (P <0.001). And the total mean concentration of PM2.5 particles in different measured positions (on platforms, ticket hall, station entrances, inside passenger cars) were significantly different (P <0.001). In such a way that the concentration of particles on the platforms was significantly higher than the entrance area of the stations and the ticket office. And the lowest concentration of airborne particles was related to the air input the station with the amount (0.015+_0.012). Based on the results, there was a significant difference between the concentration of PM2.5 particles on the platforms, ticket halls and station entrances in the daily stations and the underground stations (P <0.018). The concentration of airborne particles on the platforms was the highestThe average PM2.5 particle concentration of underground stations was higher than that of surface stations . This finding is consistent with the results of previous studies According to Armando Cartenì's study in the Italian metro, the concentration of airborne particles on the platforms of underground stations was higher than the air outside the station, while the concentration of airborne particles on the ground stations was not significantly different from the air outside. On the other hand, leaving the windows open in the underground trains increases the concentration of airborne particles, but in the above-ground stations, the open windows of the train cause clean air to enter the train, which is a natural ventilation.


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