The Research On The Dynamic Change Of PM2.5 In Subway Carriages In Beijing

In recent years,there are many hazy days in China.The haze pollution represented by fine particles is one of the most prominent environmental problem which affects people’s health in China.At present,the research on fine particulate matter at home and abroad mainly concentrates on the ground and general public places,and the research on fine particulate matter in subway mainly concentrates on public area.However,relevant studies show that passengers spend 3/4 of their time on trains,and the average time spent in public areas such as halls and platforms will not exceed 10 minutes.In the morning and evening rush hour,there is a dense crowd in the carriage,the internal space is extremely crowded,and the human body has been in the environment of no air circulation or poor circulation for a long time.Excessive concentration of fine particles seriously affects people’s physical and mental health.The environment in subway carriages is very complex,the current research lacks a large number of measured data,coupled with the lack of systematic research methods,which leads to the lack of understanding of the concentration distribution and characteristics of PM2.5 in the subway carriage.This paper tested and analyzed the PM2.5 concentration in the carriages of typical subway lines in Beijing from February 2016 to January 2019,the main test line platform doors are shielded doors,full-height safety doors and semi-high safety doors.The main test locations are carriages,platforms and outdoors.It is of great significance for PM2.5 data accumulation in subway carriages and future system research and control.After the preliminary analysis of the test results,the main conclusions are:(1)85% of the test data are polluted.It can be seen that air quality of Beijing Metro carriages is poor.(2)By testing the PM2.5 concentration in different positions of the carriage in the subway station,the main conclusions are as follows:(1)Among many factors,the type of platform gate has the greatest influence. Under the same outdoor conditions,PM2.5 concentration in the carriage of the shielded door line is generally higher than that of the non-shielded door line.(2)Statistical analysis shows that when the outdoor PM2.5 concentration is low, the PM2.5 concentration in carriages is higher than the outdoor PM2.5 concentration;when the outdoor PM2.5 concentration is higher,the PM2.5 concentration in carriages is lower than the outdoor PM2.5 concentration.Because different lines have different shielding effect on outdoor environment,the critical value of size conversion is also different.135μg/m3 for line 1,200μg/ m3 for line 8,50μg/m3 for line 10,100μg/ m3 for line 14.The general rule is: shielded door line > unshielded door line.To some extent,the critical value reflects the degree of PM2.5 accumulation in the tunnel.(3)There is fluctuation of PM2.5 concentration in train operation,and the characteristics of different types of lines are different: PM2.5 concentration in the carriage of the shielded door line fluctuate greatly,but the mean value changes slightly;The opposite law exists in the non-shielded door line.When the outdoor concentration is low,the PM2.5 concentration increases when the train accelerates and decreases when the train arrives.When the concentration was low outdoors,the results were opposite.It shows that PM2.5 in the carriage mainly comes from tunnel when the outdoor concentration is low,and when the outdoor concentration is high,it mainly comes from the outdoor;Linear lines are not conducive to air exchange between tunnels and outdoors,and PM2.5 concentration in tunnels mostly accumulates at the end.(4)When the outdoor concentration is low,the PM2.5 concentration in different railway carriages is: head > tail,and the concentration fluctuates while the train is running,and the tail lags behind(3)The distribution of particulate matter in metro station and the related factors affecting the concentration of particulate matter are analyzed.The main conclusions are as follows:(1)Outdoor PM2.5 concentration has a significant impact on the concentration of PM2.5 in the carriage.(2)Passenger flow has no significant effect on PM2.5 concentration in the carriage;(3)Temperature and humidity have a significant effect on PM2.5 concentration,but there is no significant effect under the combined action of temperature and humidity;(4)The running life of the train has a certain impact on PM2.5.Generally speaking,the longer the train is used,the higher the PM2.5 concentration is in the carriage.