Abstract
RationaleAn 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. MethodA 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. ResultsThe 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. ContributionsThe 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.
Highlights
The effects of ventilation and increased carbon dioxide (CO2) on human performance and physiology is imperfectly understood [1,2,3,4,5]
The findings of this study provide support to (a) the notion that cognitive performance decrements due to poor indoor air quality (IAQ) can precede awareness of the declining air quality [11,12], and (b) that relying on discomfort as a reminder to ventilate in naturally ventilated offices may not be sufficient to avoid productivity losses, supporting the recommendation for visual CO2 feedback in naturally ventilated buildings as a reminder to ventilate [46]
Findings suggest: (1) a lack of an expected performance improvement in executive function and cognitive flexibility parameters when CO2 is artificially raised; (2) this lack of expected improvement can occur without changes to sick building syndrome (SBS) symptoms or perceived air quality, can occur after only short duration exposures to the higher CO2 conditions, and cannot be explained by physiological, neurophysiological or subjective factors
Summary
The effects of ventilation and increased carbon dioxide (CO2) on human performance and physiology is imperfectly understood [1,2,3,4,5]. CO2 is produced as part of human respiration and is used as a proxy for ventilation rate in a room and the likely presence of other indoor pollutants such as volatile organic compounds (VOC's) including human bio-effluents [4,5]. (1) It is not conclusively determined whether CO2 is an innocuous indicator of other harmful indoor pollutants such as volatile organic compounds and human bio-effluents [1,2], or is itself an active contributor to reduced performance in cognitive tasks [7,8,9]. (2) Temporal dimensions, such as the minimum duration of exposure to poor indoor air quality (IAQ) necessary to cause a measurable reduction in cognitive performance is imperfectly understood. Studies typically utilise exposure durations in excess of two hours [2,5,7,10,11,12], yet continuous exposures of this length are unlikely
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