Is CO2 an indoor pollutant? Direct effects of low-to-moderate CO2 concentrations on human decision-making performance.
Level 2 - randomized trial
Randomized, double-blind crossover exposure trial
PubMed 23008272 · doi:10.1289/ehp.1104789
What was done
Twenty-two participants in six groups were exposed to three carbon dioxide (CO2) concentrations (600, 1,000, and 2,500 ppm) in an office-like environmental chamber. Each participant underwent three 2.5-hour exposure sessions on a single day, with exposure order balanced across groups. Ventilation rate and temperature were kept constant, with higher concentrations achieved by injecting ultrapure CO2. Participants and the test administrator were blinded to CO2 concentrations. Under each condition, participants completed a computer-based decision-making performance test and subjective questionnaires regarding health symptoms and perceived air quality. Data were analyzed using analysis of variance (ANOVA) models.
What was found
Compared with the 600 ppm baseline, exposure to 1,000 ppm CO2 resulted in moderate, statistically significant performance decrements on 6 of 9 decision-making scales. At 2,500 ppm CO2, large and statistically significant reductions occurred on 7 of 9 decision-making scales (raw score ratios ranging from 0.06 to 0.56), while performance on the focused activity scale significantly increased.
Why it matters
This study suggests that indoor CO2 directly impairs human cognitive and decision-making performance at concentrations commonly found in poorly ventilated buildings, rather than merely acting as a passive surrogate marker for other indoor pollutants.
Limits
The sample size was very small (n = 22), and all three 2.5-hour exposure conditions occurred on a single day, leaving potential carryover or fatigue effects uncertain. The abstract does not provide participant demographic characteristics, exact effect sizes for the 1,000 ppm condition, or findings from the symptom and air quality questionnaires, and laboratory computer tasks may not fully capture real-world occupational performance.
Cited by
- contradicts Adverse effects from indoor carbon dioxide levels primarily occur at concentrations of 2,000 to 3,000 parts per million, whereas levels around 1,200 to 1,300 ppm are common and generally not severely problematic.