Is CO₂ an Indoor Pollutant? Direct Effects of Low-to-Moderate CO₂ Concentrations on Human Decision-Making Performance

Usha Satish,¹ Mark J. Mendell,² Krishnamurthy Shekhar,¹ Toshifumi Hotchi,² Douglas Sullivan,² Siegfried Streufert,¹ and William J. Fisk²

¹Department of Psychiatry and Behavioral Science, Upstate Medical University, State University of New York, Syracuse, New York, USA; ²Indoor Environment Department, Lawrence Berkeley National Laboratory, Berkeley, California, USA

Abstract

Background: Associations of higher indoor carbon dioxide (CO₂) concentrations with impaired work performance, increased health symptoms, and poorer perceived air quality have been attributed to correlation of indoor CO₂ with concentrations of other indoor air pollutants that are also influenced by rates of outdoor-air ventilation.

Objectives: We assessed direct effects of increased CO₂, within the range of indoor concentrations, on decision making.

Methods: Twenty-two participants were exposed to CO₂ at 600, 1,000, and 2,500 ppm in an office-like chamber, in six groups. Each group was exposed to these conditions in three 2.5-hr sessions, all on 1 day, with exposure order balanced across groups. At 600 ppm, CO₂ came from outdoor air and participants’ respiration. Higher concentrations were achieved by injecting ultrapure CO₂. Ventilation rate and temperature were constant. Under each condition, participants completed a computer-based test of decision-making performance as well as questionnaires on health symptoms and perceived air quality. Participants and the person administering the decision-making test were blinded to CO₂ level. Data were analyzed with analysis of variance models.

Results: Relative to 600 ppm, at 1,000 ppm CO₂, moderate and statistically significant decrements occurred in six of nine scales of decision-making performance. At 2,500 ppm, large and statistically significant reductions occurred in seven scales of decision-making performance (raw score ratios, 0.06–0.56), but performance on the focused activity scale increased.

Conclusions: Direct adverse effects of CO₂ on human performance may be economically important and may limit energy-saving reductions in outdoor air ventilation per person in buildings. Confirmation of these findings is needed.

Key words: carbon dioxide, cognition, decision making, human performance, indoor environmental quality, ventilation. 

Environ Health Perspect 120:1671–1677 (2012). http://dx.doi.org/10.1289/ehp.1104789 [Online 20 September 2012]

Address correspondence to M.J. Mendell, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., 90R3058, Berkeley, CA 94720 USA. Telephone: (510) 486-5762. Fax: (510) 486-6658. E-mail: mjmendell@lbl.gov

Funding for this research was provided by Collaborative Activities for Research and Technology Innovation (CARTI), which supports research in the areas of air quality and water resource management. CARTI, part of the Syracuse Center of Excellence located in Syracuse, New York, is supported by the U.S. Environmental Protection Agency under award EM-83340401-0. Information about CARTI is available at http://www.syracusecoe.org/coe/sub1.html?skuvar=68.

The authors declare they have no actual or potential competing financial interests.

Received 28 November 2011; Accepted 20 September 2012; Online 20 September 2012.