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The impact of human exposure to indoor carbon dioxide on cognitive performance
Cognitive performance is critical to people’s daily life, especially for learning and working. Adverse impacts of carbon dioxide on people’s cognitive performance have been found by some studies, while others do not report statistically significant effects during exposures to carbon dioxide. For those studies which found an effect, some could not disentangle the direct impact of carbon dioxide from the impact of changes in ventilation rates. This work will provide further clarity on the interrelationship between cognitive performance, carbon dioxide and ventilation strategies based on experimental studies.
72 participants will be recruited for this experiment conducted at the environmentally controlled chamber at UCL HereEast. A validated computerized neurobehavioral test battery (BARS) will be used to assess participants’ cognitive performance during the exposure. The Behavioral Assessment and Research System (BARS) is a computer-based testing system, which aims to assess people’s neurobehavioral function. It provides a battery of neurobehavioral tests optimized for the detection of neurotoxicity in non-mainstream human populations, especially people with limited education and literacy. It includes tests of attention, memory, learning motivation, complex function, response speed and coordination. Scheduled participants will be randomly assigned to one of two ventilation rates conditions (Condition 1: 8L/sec per person; or Condition 2: 15L/sec per person), i.e. half the participants in each ventilation rate condition. Within each group with a fixed ventilation rate, eight people at a time will be exposed, in three separate sessions, each lasting one hour, to three conditions of carbon dioxide levels (600ppm, 1500ppm and 2100ppm). The interval between two experiment sessions will be at least four weeks to minimize learning effects of the cognitive tests.
At 600ppm, carbon dioxide comes mostly from background levels and participants’ respiration. Higher concentrations will be achieved by injecting pure carbon dioxide into the chamber. During each condition, temperature, humidity, lighting intensity and noise levels are kept constant. (temperature: 23˚C, relative humidity (RH): 50%, illuminance: 300lx; noise level will be kept stable by giving participants noise cancelling headphones). Concentration levels of PM, TVOCs and Ozone inside the chamber are monitored to ensure that all pollutants are exposed to similar levels of pollution. Under each condition (blind to participants), participants will also be asked to report, via a paper-based questionnaire, their comfort levels, perceived air quality and any acute health symptoms.
The impacts of interactions between carbon dioxide and ventilation on cognitive performance, will be disentangled in this project with participants testing under two ventilation rate groups. The result might have implications for existing building standards that specify ventilation rates, in terms of worldwide trends of energy saving and taking cost reduction into consideration. It also aims to raise awareness about the potential impact that climate change might have on people’s cognitive performance and explore more robust building ventilation strategies.