In-vehicle carbon dioxide concentration in commuting cars in Bangkok, Thailand.

It is known that in-vehicle carbon dioxide (CO2) concentration tends to increase due to occupant exhalation when the HVAC (heating, ventilation, and air conditioning) air is in recirculation mode. Field experiments were conducted to measure CO2 concentration during typical commute in Bangkok, Thailand. The measured concentrations agreed with the concentration predicted using first-order mass balance equation, in both recirculating and outside air modes. The long-term transient decay of the concentration when the vehicle was parked and the HVAC system was turned off was also studied. This decay was found to follow Fickian diffusion process. The paper also provides useful operational details of the automotive HVAC system and fresh air ventilation exchange between cabin interior and exterior. IMPLICATIONS: Drivers in tropical Asian countries typically use HVAC recirculation mode in their automobiles. This behavior leads to excessive buildup of cabin CO2 concentration levels. The paper describes the CO2 buildup in a typical commute in Bangkok, Thailand. Auto manufacturers can potentially take measures to alleviate such high concentration levels. The paper also discusses the diffusion of CO2 through the vehicle envelope, an area that has never been investigated before.