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Development and Application of an Indoor Carbon Dioxide Metric



Andrew K. Persily


Indoor carbon dioxide (CO2) concentrations have been considered for decades in evaluating indoor air quality (IAQ) and ventilation, and more recently in discussions of the risk of airborne infectious disease transmission. However, many of these applications reflect a lack of understanding of the connection between indoor CO2 levels, ventilation and IAQ. For example, a single indoor concentration such as 1000 ppmv is often used as a metric of good IAQ and ventilation without an understanding of the significance of this or any other value. CO2 concentrations are of limited value as IAQ metrics, and a single concentration will not serve as a ventilation indicator for spaces with different occupancies and ventilation requirements. An approach has been developed to estimate a space-specific CO2 level that can serve as a metric of the outdoor ventilation rate per person. The concept is to estimate the CO2 concentration that would be expected in a specific space type given its intended or expected ventilation rate per person, the number of occupants, the rate at which they generate CO2 and the time that has transpired since the space was occupied. This paper describes the approach and presents example calculations for several commercial, institutional and residential occupancies.
Indoor Air-International Journal Of Indoor Air Quality And Climate


carbon dioxide, indoor air quality, metrics, occupancy, standards, ventilation


Persily, A. (2022), Development and Application of an Indoor Carbon Dioxide Metric, Indoor Air-International Journal Of Indoor Air Quality And Climate, [online],, (Accessed July 25, 2024)


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Created July 19, 2022, Updated November 29, 2022