In southern states (e.g., Arizona) typically people drive their vehicles in summer by running vehicle’s air conditioning systems in recirculation modes only. Carbon dioxide exhaled by occupants remains within the cabin during operation in recirculation mode. The concentration of carbon dioxide starts increasing in the cabin. The CO2 that is inhaled by the occupants goes into their blood stream that negatively affects occupant’s health. ASHRAE Standard 62 specifies the safe levels of carbon dioxide in conditioned space for humans. The CO2 concentration limit per ASHRAE is 700 ppm over the ambient conditions on a continuous basis. Current global average ambient concentration level of CO2 as of March 2015 (NOAA, 2016) is approximately 401 ppm. Hence, if the CO2 concentration exceeds approximately 1100 ppm inside of a home or a vehicle cabin, then we must introduce outside air into the home or vehicle cabin to reduce the CO2 concentration. The author has been conducting work in this area (Mathur, 2016, 2007) for the past 10 years. In this investigation, the author will present a summary of the model development that can be used for prediction of cabin carbon dioxide levels for automobiles based on many variables. This are a number of parameters including number of occupants that dictates generation of CO2 within the control volume, cabin leakage (infiltration or exfiltration) characteristics, cabin volume, blower position or airflow rate; vehicle age, etc. Detailed results will be presented in the paper. REFERENCES 1. ASHRAE/ANSI, Standard 62-1999, Ventilation for acceptable indoor air quality, American Society of Heating Refrigerating and Air Conditioning Engineers., Inc., Atlanta, GA, 1999. 2. http://www.esrl.noaa.gov/gmd/ccgg/trends/ 3. Mathur, G.D. 2016 Experimental investigation to determine influence of build-up of cabin carbon dioxide concentrations for occupants fatigue, SAE Paper # 2016-01-0254. 3. Mathur, G.D. 2007. Monitoring build-up of carbon dioxide in automobile cabin to improve indoor air quality (IAQ) and safety, Vehicle Thermal Management Systems, Nottingham, UK, Paper # 051, May.