The electrical resistances of small-sized activated carbon fiber (ACF) fabric (specific surface area: 1244.7 m2/ g, average pore diameter: 1.92 nm) and felt (specific surface area: 1321.2 m2/ g, average pore diameter: 2.21 nm) sensors were measured in a temperature and humidity controlled gas chamber by CO2 adsorption at different surrounding CO2 concentrations (3000–10,000 ppm). The electrical resistances of ACF sensors decreased linearly as the increase of temperature and decreased exponentially as the increase of humidity in the ambient atmospheric chamber. The electrical resistances of ACF rapidly decreased within 4 s and an equilibrium state was achieved within 10 s due to the very rapid CO2 adsorption at room temperature and 40% humidity. Comparing the difference in electrical resistance values measured during injection of similar concentrations of CO2 after reaching the equilibrium value, the fabric exhibited a significant change, whereas the felt did not, even though it had a relatively larger specific surface area. The reason is that micropore volume greatly affected the amount of CO2 adsorbed, whereas the specific surface area did not affect it as much. Therefore, ACF fabric with large micropores (> 2.0 nm) can be developed and used as CO2 sensors in small rooms such as a passenger vehicles.

The South Korean Ministry of the Environment has revised the laws relating to the management of interior air quality for multiple use facilities, and recommends maintaining carbon dioxide (CO2) concentration in passenger vehicles below 1000 ppm during operation in urban areas of large cities. However, the interior CO2 concentration of passenger vehicles can rapidly increase and exceed 5000 ppm within 30 min, as observed when two passengers are traveling in urban areas of the South Korean city of Jeonju with the air conditioner blower turned off and the actuator mode set to internal circulation mode. With four passengers, CO2 concentration can reach up to 6000 ppm within 10 min. To counter this, when the actuator is set to external mode, CO2 concentration can be maintained below 1000 ppm, even after a long period of running time. As part of the air conditioning system, alkali-treated activated carbon fiber filters are considered to be far superior to the commercial non-woven filters or combination filters currently commonly in use.