title: Is CO2 an indoor pollutant? Direct effects of low-to-moderate CO2 concentrations on human decision-making performance.
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.
  
  
  OBJECTIVE
  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.
authors.affiliation: Department of Psychiatry and Behavioral Science, Upstate Medical University, State University of New York, Syracuse, New York, USA.
authors.forename: Usha
authors.initials: U
authors.lastname: Satish
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Mendell
authors.forename: Krishnamurthy
authors.initials: K
authors.lastname: Shekhar
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Hotchi
authors.forename: Douglas
authors.initials: D
authors.lastname: Sullivan
authors.forename: Siegfried
authors.initials: S
authors.lastname: Streufert
authors.forename: William J
authors.initials: WJ
authors.lastname: Fisk
mesh_terms: D000293:Adolescent; D000328:Adult; D000393:Air Pollutants / Q000009:adverse effects* / Q000032:analysis; D016902:Air Pollution, Indoor / Q000009:adverse effects* / Q000032:analysis; D000704:Analysis of Variance; D002245:Carbon Dioxide / Q000009:adverse effects* / Q000032:analysis; D003657:Decision Making / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004781:Environmental Exposure; D004784:Environmental Monitoring; D005260:Female; D006801:Humans; D008297:Male; D011795:Surveys and Questionnaires; D014691:Ventilation; D055815:Young Adult
chemical_list: D000393:Air Pollutants; D002245:Carbon Dioxide