A US study claims that even moderately high indoor concentrations of carbon dioxide (CO2) could be bad for decision making.
The study was conducted with researchers from State University of New York (SUNY) Upstate Medical University, the journal Environmental Health Perspectives reports.
The results were surprising and may have implications for schools and offices with high occupant density.
"In our field we have always had a dogma that CO2 itself, at the levels we find in buildings, is just not important and doesn't have any direct impacts on people. So these results, which were quite unambiguous, were surprising," said study co-author and Berkeley Lab scientist William Fisk.
On nine scales of decision-making performance, test subjects showed significant reductions on six of the scales at CO2 levels of 1,000 parts per million (ppm) and large reductions on seven of the scales at 2,500 ppm, according to a Berkeley statement.
The most dramatic declines in performance, in which subjects were rated as "dysfunctional," were for initiative and thinking strategically.
"Previous studies have looked at 10,000 ppm, 20,000 ppm; that's the level at which scientists thought effects started," said Berkeley Lab scientist Mark Mendell, study co-author. "That's why these findings are so startling."
Berkeley researchers found that even moderately elevated levels of indoor CO2 resulted in lower scores on six of nine scales of human decision-making performance.
The primary source of indoor CO2 is humans. While typical outdoor concentrations are around 380 ppm, indoor concentrations can go up to several thousand ppm. Higher indoor CO2 concentrations relative to outdoors are due to low rates of ventilation, which are often driven by the need to reduce energy consumption.
In classrooms, concentrations frequently exceed 1,000 ppm and occasionally exceed 3,000 ppm. CO2 at these levels has been assumed to indicate poor ventilation, with increased exposure to other indoor pollutants of potential concern, but the CO2 itself at these levels has not so far been a source of concern.