You may have noticed after hours of being cooped up in a meeting room, the air becomes warmer and stuffier compared to the rest of the office. This is because small rooms can build up carbon dioxide and heat from our breath, thus changing the temperature in the room. A study suggests that indoor air matters more than we have realized.

There have been eight studies in the last seven years that have looked at what happens in a room that is accumulating carbon dioxide which is the main ingredient in our exhalations. The results may have been inconsistent but they are intriguing.

It suggests that air pollution that is known to cause cancer and asthma is a more pressing public health concern, there are pollutants whose effects are on the mind rather than the body. Most buildings in the city have grown better sealed in the last few decades and it helps reduce the energy that is used in cooling and heating. It also made it easier for gasses and other substances released by humans to build up inside.

Indoor air quality may not be as well monitored as the air outdoors, but scientists and ventilations professionals have monitored carbon dioxide indoors extensively. Higher CO2 levels often indicate a low ventilation rate. Substances emitted by office supplies, carpets, and new furniture could be accumulating in the air.

 "It's long been thought of as an indicator of how bad the air in a space might be," said Brent Stephens, a professor of architectural engineering at Illinois Institute of Technology.

Indoor air pollutants are linked to cancers and respiratory problems, but carbon dioxide has been considered harmless. However, researchers have started re-examining that assumption. Inhalation of carbon dioxide at higher levels has been found by biomedical researchers to dilate blood vessels in the brain, decrease the amount of communication between brain regions and reduce neuronal activity. But lower amounts of carbon dioxide and its effect on the brain has not been studied much.

About ten years ago, William Fisk, a mechanical engineer at Lawrence Berkeley National Laboratory, and his colleagues put people in rooms where the carbon dioxide levels varied. They exposed their subjects for hours to concentrations as low as 600 ppm, which is low for indoors, and as high as 2,500 ppm, which is high but not uncommon in crowded places.

They had their subjects take a problem-solving test that measured their productivity and decision-making skills. The test generates scores for broad attributes like basic initiative and strategy. The team found a strong relationship between seven of the nine headings they looked at and carbon dioxide levels. It showed that the higher the carbon dioxide, the worse the test-takers did.

 "It's a very, very well-conceived study, with control for everything," said Pawel Wargocki, a professor of civil engineering at the Technical University of Denmark. "They were very, very careful with the details of the design."

 "What we saw were these striking, really quite dramatic impacts on decision-making performance, when all we did was make a few minor adjustments to the air quality in the building," said Joseph Allen, a professor at the Harvard T.H. Chan School of Public Health who led the study.

"Importantly, this was not a study of unique, exotic conditions," he added. "It was a study of conditions that could be obtained in most buildings, if not all."

 So far, studies have not measured the stress levels of their subjects or taken other readings that could help explain why carbon dioxide sometimes affect cognition. Astronauts and submarine crews are trained to make decisions under stress and they function normally under conditions that would perturb others.