The objective of this study is to provide the research data on the actual concentrations of $PM_{10},;PM_{2.5},;PM_1;and;CO_2$ in Seoul subway carriages. Mean concentrations of $PM_{10},;PM_{2.5};and;PM_1,;and;CO_2$ in subway carriages were investigated at levels of $215.1{pm}101.4{mu}g/m^3,;86.9{pm}38.6{mu}g/m^3,;27.0{pm}11.4{mu}g/m^3,;and;1,588{pm}714ppm$, respectively. The mean concentrations in subway carriages were higher when the train ran on an underground track rather than on an above ground track. The measured concentration of particulate matter varied with the time of day and was highest in the morning, followed by noon and evening while the $CO_2$ concentration was highest in the morning, followed by evening and noon. In relation to correlation among the pollutants: the correlation between $PM_{10};and;PM_{2.5}$ was 0.92, and that between $PM_{2.5};and;PM_1$ was 0.94. The inclusion rate of $PM_{2.5};to;PM_{10}$ was $41{pm}7%$ and that of $PM_1;to;PM_{2.5};was;32{pm}4%$. In addition, the $CO_2$ concentration had a positive relation with the number of people in a carriage, whereas the concentration of $PM_{10}$ had negative correlation to the number of people. In relation to these two pollutants we calculated using a regression equation (34.06+0.04$CO_2$(ppm)-0.09 PM10$({mu}g/m^3)$($R^2$=0.30, p<0.01, n=707), that a maximum number of 61 persons would ensure that each pollutant is maintained below the criteria level, applicable to subway stations.