Physiology or Psychology: What Drives Human Emissions of Carbon Dioxide and Ammonia?

Humans are the primary sources of CO₂ and NH₃ indoors. Their emission rates may be influenced by human physiological and psychological status. This study investigated the impact of physiological and psychological engagements on the human emissions of CO₂ and NH₃. In a climate chamber, we measured CO₂ and NH₃ emissions from participants performing physical activities (walking and running at metabolic rates of 2.5 and 5 met, respectively) and psychological stimuli (meditation and cognitive tasks). Participants' physiological responses were recorded, including the skin temperature, electrodermal activity (EDA), and heart rate, and then analyzed for their relationship with CO₂ and NH₃ emissions. The results showed that physiological engagement considerably elevated per-person CO₂ emission rates from 19.6 (seated) to 46.9 (2.5 met) and 115.4 L/h (5 met) and NH₃ emission rates from 2.7 to 5.1 and 8.3 mg/h, respectively. CO₂ emissions reduced when participants stopped running, whereas NH₃ emissions continued to increase owing to their distinct emission mechanisms. Psychological engagement did not significantly alter participants' emissions of CO₂ and NH₃. Regression analysis revealed that CO₂ emissions were predominantly correlated with heart rate, whereas NH₃ emissions were mainly associated with skin temperature and EDA. These findings contribute to a deeper understanding of human metabolic emissions of CO₂ and NH₃.