Exploring the physiological, neurophysiological and cognitive performance effects of elevated carbon dioxide concentrations indoors

Rationale: An accumulation of CO₂ in occupied indoor spaces is correlated to negative impacts on concentration, sleepiness and aspects of cognitive performance. However, factors such as: (a) the relative effect of CO₂ itself compared to other pollutants; (b) the minimum necessary exposure time for cognitive performance to be affected; and (c) the physiological drivers of cognitive performance reductions due to increased indoor CO₂ concentrations are not yet clear.

Method: A within-subjects counterbalanced study design was used to test cognitive performance, subjective and physiological parameters of 31 volunteers during short (< 60 min) exposures to normal CO₂ (830 ppm) and high CO₂ (2700 ppm, raised by introducing pure CO₂ alongside the occupant generated CO₂). The study was conducted in a small naturally ventilated office and EEG was used as an objective indicator of sleepiness.

Results: The addition of pure CO₂ to the room resulted in the absence of an expected learning effect in two cognitive performance test battery components which could not be explained by any of the physiological, psychological, or reported comfort, sick building syndrome and health variables measured. However, participants who had slept less the previous night appeared more susceptible to becoming sleepier as a result of the increased CO₂.

Contributions: The results suggest (1) the addition of pure CO₂ may influence aspects of cognitive performance after only short exposures (2) these changes occur in the absence of clear physiological drivers, (3) lack of sleep may mediate people's response to higher CO₂ concentration.