Zhao, Zeyu; (2025) The Impact of Exposure to Indoor Volatile Organic Compounds (VOCs) on Human Cognitive Performance. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In educational buildings, poor air quality can adversely affect learning and creativity. Volatile Organic Compounds (VOCs) are common indoor air pollutants; existing evidence indicates that high Total Volatile Organic Compounds (TVOC) levels can lead to health issues and reduced cognitive performance. However, the effects of acute exposure to lower TVOC levels are not well documented. The rising average temperatures and increasing frequency of heatwaves contribute to overheating in buildings. Prolonged high indoor temperatures could further exacerbate TVOC emissions, while the combined impact of temperature and TVOC level on cognitive performance remains unclear. Therefore, it is crucial to investigate the effects of indoor TVOC levels and temperatures on learning-related cognitive performance in university students. This PhD project explored the topic through two independent single-blind experiments conducted in a human climate chamber. Experimental Study 1 utilized three TVOC concentrations (100, 1000, and 2000 µg/m3) and involved 33 university students. Experimental Study 2 adopted two temperatures (23°C and 28°C) and two TVOC concentrations (100 and 1000 µg/m³), with 71 university students participating. A pilot study was conducted to verify proper climate chamber operation and confirm the use of paint as the VOC source. Cognitive performance was assessed using the BARS cognitive test battery; participants provided their subjective experience of the environment via paper-based questionnaires before and after the experiment. The research concluded that from the perspective of TVOC exposure, the cognitive impact of 1000 µg/m³ TVOC was inconclusive. Accuracy significantly reduced by 4.9% when acutely exposed to 2000 µg/m³ TVOC compared to the 100 µg/m³ level, while its effect on reaction speed was unclear. From the perspective of combined exposure to TVOC and temperature, exposure to 28°C significantly reduced task accuracy compared to 23°C, while its effect on reaction speed remained unclear. The cognitive impact of 1000 µg/m³ TVOC also remained uncertain. No interaction effect was observed between temperature and TVOC levels. Participants reported significantly poorer air quality perceptions under higher TVOC exposure and elevated temperatures. Eye irritation, fatigue, and dizziness were the most commonly reported symptoms, potentially linked to xylene exposure. Test duration and first language were key confounders in both experimental studies, long test duration reduced cognitive performance and Chinese speakers performed better on number-based tasks. In summary, only accuracy performance was significantly affected under higher TVOC (2000 µg/m³) and higher temperature (28°C), respectively. The impact of these conditions on reaction speed remained inconclusive. The effects of moderate TVOC levels (1000 µg/m³) on both accuracy and reaction speed were also unclear. These findings offer valuable insights for enhancing indoor air quality standards and building design. From a cognitive perspective, the current standard appears acceptable for university buildings. However, to better protect well-being and cognitive function in a broader range of educational settings, adopting stricter, scenario-specific TVOC limits may be beneficial. Additionally, newly constructed and renovated buildings may prioritize low-VOC materials, early air quality monitoring, and energy-efficient mitigation strategies.

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