Chen, Didong; (2025) An Experimental Study on the Effects of Short-term Exposure to Low-to-medium Pure Carbon Dioxide on University Students’ Cognitive Performance. Doctoral thesis (Ph.D), UCL (University College London).

Text PhD Thesis- Didong Chen.pdf - Accepted Version Access restricted to UCL open access staff until 1 July 2026. Download (20MB)

Abstract

Educational buildings frequently experience elevated indoor CO2 concentrations due to inadequate ventilation and high occupancy, sometimes exceeding levels of relevant guidelines such as Building Bulletin 101. Elevated indoor CO2 concentrations pose concerns regarding human health and cognitive performance. Some studies reported detrimental impacts on cognitive performance of indoor CO2 levels, while others did not, which perhaps could be due to the presence of other pollutants in studies where CO2 was only a proxy for ventilation. To generate further evidence regarding whether pure CO2 within the guideline range impacts cognitive performance in the absence of other major known pollutants, an experimental study with a fixed high ventilation rate was conducted in an environmentally controlled chamber. In a crossover design, sixty-nine healthy university students were exposed individually for seventy minutes, in three separate sessions, to three CO2 conditions of 600 (baseline), 1500 and 2100 ppm. A validated neurobehavioral BARS test battery was used to assess participants’ cognitive performance. A two-step statistics analysis was conducted in this thesis to investigate the effects of elevated pure CO2 levels below 2100 ppm and cognitive performance measured by the BARS test battery. In the first phase of statistics analysis, univariable and multivariable analysis were used to examine the association between varied pure CO2 concentrations and outcomes of each cognitive test from two perspective, speed and accuracy. Comparing elevated CO2 levels to 600 ppm, after adjusting for potential confounders, results showed significant improved speed performance in two out of ten tests, and no significant differences in accuracy for any test. In the second phase of statistics analysis, in addition to analysing the test results separately, aggregation of the tests by cognitive domains were achieved with factor structure generated from the exploratory factor analysis of BARS tests. Associations between elevated pure CO2 levels and factor scores which represent participants’ placement on cognitive domains were examined, and no significant difference was found for any of the domains across three CO2 conditions. The majority of the findings from the statistics analysis provide empirical evidence that the cognitive performance of university students, measured by the BARS test battery, was not adversely affected by pure CO2 at levels routinely experienced in the educational building environment, consistent with current building guidelines and 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. More importantly, not only that some of the results from prior studies which reported decrements in cognitive performance could not be confirmed in this study, the contrary was found. This adds to the uncertain nature of evidence in this field, although more research is needed to confirm this finding which could be due to arousal effects or to numerous testing across several variables.

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