Effects of short-term exposure to moderate pure carbon dioxide levels on cognitive performance, health symptoms and perceived indoor environment quality

Educational buildings frequently experience elevated CO2 concentrations with inadequate ventilation and high occupancy, sometimes exceeding building guideline levels. Some studies reported detrimental impacts on cognitive performance of indoor CO2 levels, while others did not. To generate further evidence, we conducted an experiment in an environmentally controlled chamber. Sixty-nine healthy university students were exposed individually for 70 min, in three separate sessions, to three CO2 conditions of 600, 1500 and 2100 ppm (crossover design). With fixed ventilation rates, pure CO2 was injected to achieve different exposure levels. A validated neurobehavioral BARS test battery was used to assess participants' cognitive performance. Participants gave subjective ratings of indoor environment and reported any health symptom through questionnaires. Comparing elevated CO2 levels to 600 ppm, after adjusting for potential confounders, results showed significant improved performance, that is, responses were quicker in two out of ten tests, and no significant differences in accuracy for any test. Under 1500 ppm, participants rated the air quality significantly higher than at 600 ppm, but there were no differences at 2100 ppm. Differences were not significant on thermal sensation, perceived lighting quality, perceived noise level, or health symptoms for comparisons between conditions. Results indicate no clear link between pure CO2 levels below 2100 ppm and cognitive performance, perceived indoor environment quality and health symptoms. The findings are consistent with some prior studies, indicating that pure CO2 below 2100 ppm implies no harm in adults and should not be treated as a potential indoor pollutant in higher educational environments.