You might think it's your colleagues or the pressures of work that's getting you down at the office, but new research suggests it could well be the air you're breathing instead. Scientists in the US have found that the concentration of carbon dioxide inside the confined spaces we use every day could be high enough to damage our health.

Of course, it's well established that high levels of CO2 are dangerous, not just for human beings but for the planet as a whole, but the new research raises questions about carbon dioxide concentrations that were previously considered harmless.

The researchers gathered together 24 volunteers and tested their performance in three different simulated office environments. The key metric here is parts-per-million (ppm) of CO2: 5,000 ppm is currently considered the safe limit for an 8-hour workday, while 90,000 ppm will kill you within f5 minutes.

The team experimented with three different levels over the course of a standard 9-to-5 routine: 550 ppm (similar to outdoor levels), 945 ppm (what you would expect in most offices) and 1,400 ppm (denser but still plausible for many offices).

By giving the participants a cognitive test at the end of the day, they were able to spot a clear trend between CO2 levels and brain function. Those working with 945 ppm of carbon dioxide in the air averaged scores that were 15 percent lower than those in a 550 pm room. The unfortunate workers who had to handle levels of 1,440 ppm, meanwhile, performed 50 percent worse than the 550 ppm group. People's ability to use information, respond to a crisis and strategise were hit particularly hard, the researchers said.

Indoor concentrations are affected by many different factors: not just the ventilation installed inside the building and how many windows are open, but also the number of people in the room - because we breath out carbon dioxide - and even how much CO2 is floating around in the neighbouring streets.

The researchers, from Harvard and Syracuse University, say carbon dioxide should be considered direct pollutant and not just a marker for other pollutants, plus more research is now required to see how even low levels of CO2 can impair brain function.

"These exposures should be investigated in other indoor environments, such as homes, schools and airplanes, where decrements in cognitive function and decision-making could have significant impacts on productivity, learning and safety," concludes the report, published in the journal Environmental Health Perspectives.

In the meantime, you might want to ask your boss if you can open up a window.