The effects of carbon dioxide exposure concentrations on human vigilance and sentiment in an enclosed workplace environment

Exploring a pathway to optimise the carbon tax policy in terms of the economy, the environment and health: A scenario-based system dynamics approach

The carbon tax, a pivotal policy instrument in tackling climate change, holds the potential to significantly influence the development of society. To comprehensively analyse the effectiveness of the policy on carbon taxation and explore its possible optimisation path, this study utilizes system dynamics theory to establish a simulation model. A detailed analysis and evaluation of this policy is then conducted from the perspectives of the economy, the environment, and health. To guarantee the precision of the simulation model, a new, comprehensive evaluation method is proposed, which can test the degree of fit of the relative trend and absolute data of the simulation model with reality. The findings reveal that, despite its negative economic implications, a carbon tax policy has positive ramifications for the environment, energy, health, industrial structure, and carbon intensity targets. Furthermore, the synergistic reinforcement effect of R&D and new energy support policies on carbon taxation surpasses the impact of any individual policy alone. Notably, the influence of auxiliary policies has a temporal difference on this policy. Based on these insights, the study concludes with practical policy recommendations.

Effects of increased recirculation air rate and aircraft cabin occupancy on passengers' health and well-being - Results from a randomized controlled trial

BACKGROUND

Aircraft cabins are special environments. Passengers sit in close proximity in a space with low pressure that they cannot leave. The cabin is ventilated with a mixture of outside and recirculated air. The volume of outside air impacts the carbon footprint of flying. Higher recirculation air rates could be considered to save energy and divert less kerosene from producing thrust.

OBJECTIVES

To investigate whether higher recirculation air rates in aircraft cabins negatively affect passengers' health and well-being and if occupancy plays a role in this.

METHODS

In a 2 (occupancy: full and half-occupied) X 4 (ventilation regime) factorial design with stratified randomization, participants were exposed in an aircraft segment in a low-pressure tube during a 4-h simulated flight. Ventilation regimes consisted of increasing proportions of recirculated air up to a maximum CO₂ concentration of 4200 ppm. Participants rated comfort, health symptoms, and sleepiness multiple times. Heart rate (variability), as stress marker, was measured continuously.

RESULTS

559 persons representative of flight passengers regarding age (M = 42.7, SD = 15.9) and sex (283 men) participated. ANCOVA results showed hardly any effect of both factors on self-reported health symptoms, strong main effects of occupancy on comfort measures, and interaction effects for sleepiness and physiological stress parameters: Participants in the half-occupied cabin hardly reacted to increased recirculation air rates and show overall more favorable responses. Participants in the fully occupied cabin reported higher sleepiness and had stress reactions when the recirculation air rate was high.

DISCUSSION

This large-scale RCT shows the importance of occupancy, a previously neglected factor in indoor air research. The proximity of other people seems to increase stress and exacerbate reactions to air quality. Further studies on causal pathways are needed to determine if recirculation air rates can be increased to reduce the carbon footprint of flying without detrimental effects on passengers.

Carbon dioxide effects on daytime sleepiness and EEG signal: A combinational approach using classical frequentist and Bayesian analyses

Environmental carbon dioxide (CO₂ ) could affect various mental and physiological activities in humans, but its effect on daytime sleepiness is still controversial. In a randomized and counterbalanced crossover study with twelve healthy volunteers, we applied a combinational approach using classical frequentist and Bayesian statistics to analyze the CO₂ exposure effect on daytime sleepiness and electroencephalogram (EEG) signals. Subjective sleepiness was measured by the Japanese Karolinska Sleepiness Scale (KSS-J) by recording EEG during CO₂ exposure at different concentrations: Normal (C), 4000 ppm (Moderately High: MH), and 40 000 ppm (high: H). The daytime sleepiness was significantly affected by the exposure time but not the CO₂ condition in the classical statistics. On the other hand, the Bayesian paired t-test revealed that the CO₂ exposure at the MH condition might induce daytime sleepiness at the 40-min point compared with the C condition. By contrast, EEG was significantly affected by a short exposure to the H condition but not exposure time. The Bayesian analysis of EEG was primarily consistent with results by the classical statistics but showed different credible levels in the Bayes' factor. Our result suggested that the EEG may not be suitable to detect objective sleepiness induced by CO₂ exposure because the EEG signal was highly sensitive to environmental CO₂ concentration. Our study would be helpful for researchers to revisit whether EEG is applicable as a judgment indicator of objective sleepiness.

Associations of Human Cognitive Abilities with Elevated Carbon Dioxide Concentrations in an Enclosed Chamber

Fifteen participants were exposed in an enclosed environmental chamber to investigate the effects of elevated carbon dioxide (CO2) concentration on their cognitive abilities. Three CO2 conditions (1500, 3500, and 5000 ppm) were achieved by constant air supply and additional ultrapure CO2. All participants received the same exposure under each condition, during which they performed six cognitive tests evaluating human perception, attention, short-term working memory, risky decision-making, and executive ability. Generalized additive mixed effects model (GAMM) results showed no statistically significant differences in performance on the reaction time (RT) tests, the speed perception test, and the 2-back test. This suggests that elevated CO2 concentrations below 5000 ppm did not affect participants’ perception and short-term working memory. However, a significant increase in response time was observed in the visual search (VS) test, the balloon simulation risk test (BART), and the Stroop test at 5000 ppm compared to lower exposure concentrations. The slower responses reflected the detrimental effects of elevated CO2 concentrations on visual attention, risky decision-making, and executive ability. The findings suggest that the control level of CO2 concentrations should be tighter in enclosed workplaces where rapid response and operational safety are required.

Physiological responses, self-reported health effects, and cognitive performance during exposure to carbon dioxide at 20 000 ppm

In this study, 24 subjects (20-58 years) were exposed to carbon dioxide (CO₂ ) at 770 ppm and 20 000 ppm in an exposure laboratory for 4-h, including 2 × 15 min of cycling to investigate the effects on acid-base balance, physiological responses, cognitive performance and acute health. Capillary blood analysis, heart rate, respiratory rate, divided attention, flexibility, and sustained attention from the Test Battery for Attentional Performance (TAP), critical flicker fusion frequency (CFF), and self-reported symptoms were measured before, during, and after the 4-h exposure. Blood pH decreased and partial pressure of carbon dioxide (pCO₂ ) increased significantly when exposed to 20 000 ppm CO₂ compared to 770 ppm. However, the values remained within the normal range. In addition, respiratory rate increased slightly but significantly at 20 000 ppm CO₂ . No significant changes in heart rate, CFF, task performance or acute health were found. In sum, the findings suggest that the observed changes in acid-base balance and ventilation can be classified as physiological adaptation responses. Impairment of cognitive performance is not expected from exposure to 20 000 ppm CO₂ , neither as direct effect on central nervous system function nor as a distraction related to perception of health effects.