Above: Schoolchildren bored in a classroom - Image © Goldfaery, iStockPhoto.com

You have been stuck in your classroom for the whole afternoon, and there is another half hour until it is time to go home. You have a pounding headache. You cannot focus or think properly. What’s going on?

It just might have something to do with the air you are breathing. Let’s look at what happens to your mind and body when the air you breathe has more carbon dioxide (CO2) than it should.

What happens when you breathe?

Your body uses oxygen to create the energy you need to live. When you breathe oxygen into your lungs, oxygen catches a ride on your red blood cells. This way, it reaches your organs and muscles.

Did you know? Air is made up of a combination of different gases (not just oxygen!). The main components are:
78% Nitrogen
21% Oxygen
0.93% Argon
0.04% Carbon Dioxide

Through a complex process called cellular respiration, oxygen goes through a series of chemical reactions in order to form energy, CO2, and water vapour. Using that energy, your heart can pump, your brain can think, and your muscles can contract. Meanwhile, that CO2 and water vapour are released into the environment.

What’s the problem?

Scientists have found that high levels of CO2 in the air can affect you physically and mentally. Inside, when there are lots of people and poor ventilation, the concentration of CO2 may get high. It may even increase to levels much higher than if you were outside!

Can you imagine the amount of CO2 released in your classroom by your classmates, teacher, and yourself throughout the day?

High levels of CO2 in the air can reduce the amount of oxygen you breathe in. Over long periods of time, the reduced oxygen supply to your brain might make it difficult for you to stay awake in class, pay attention to your teacher, or concentrate on tests. In one study, scientists found that high levels of CO2 can even reduce your ability to make decisions.

Too much CO2 can also make you feel physically bad. You might start to get a headache, feel dizzy or nauseous, get tired, or have trouble breathing. Poor indoor air quality may also worsen allergies, asthma symptoms and lung health.

How much is too much?

To put a number to it, the average outdoor atmospheric levels of CO2 is around 400 ppm (parts per million). Different people start to feel effects at different CO2 levels. Some people start to feel tiredness and other effects at CO2 levels above 1,000 ppm.

To get a better appreciation of 1,000 ppm, let’s look at what it means. A ppm is a unit of concentration. 1 ppm means that you have 1 of something in a million of something else. The “something” and “something else” can be measured in molecules, masses, volumes, or whatever else you can think of. Normally, when we are talking about things in the air, we are talking about volumes (which is why sometimes you’ll also see ppmv or “part per million by volume”)
Getting back to CO2, let’s say your classroom holds a volume of 1,000 L of air and has a CO2 level of 1,000 parts per million.
1,000 L * 1,000 parts/1,000,000 = 1 L.
In other words, there is 1 L of CO2 in your 1,000L classroom.

Headaches and the other physical effects described above can begin at around 2,000-5,000 ppm. Above 5,000 ppm some more serious, and potentially toxic, effects could occur.

Again, these effects happen because when there is more carbon dioxide in the air, there is usually less oxygen. We need oxygen to survive!

It is important to maintain low CO2 levels. Toronto Public Health recommends that classroom levels remain between 800 and 1,000 ppm. CO2 can be measured using a simple electronic meter that people can buy in a store or online. But it’s often best to hire a professional as they can check for any other causes for the high levels.

CO2 in your classroom

So, when you are sitting in your classroom, how much CO2 are you actually being exposed to? Between 2010 and 2015, 106 Toronto schools had an air quality test done. 43% of those schools had one or more classrooms with a CO2 concentration above 1,000 ppm. This means schools need to do a better job at ventilating some of their classrooms!

Remember, 1,000 ppm is not high enough to immediately hurt you. But it is high enough to cause some physical effects that can affect your grades.

A 2015 study based in the southwestern United States found that students in classrooms with higher concentrations of CO2 had lower test scores. In a similar study, scientists exposed 24 office workers to varying conditions. They found that, between CO2 concentrations of 400 - 1600 ppm, higher levels of CO2 were generally associated with lower cognitive score. In other words, people working in higher CO2 levels may be less able to make plans and decisions.

So if you don’t feel well in a classroom, and think the air might have something to do with it, what can you do? You may want to open a window, leave the door open, or take a break and breathe in the fresh air outside.

CO2 levels affect everyone differently, so not all of your classmates will feel the same way you do. But if CO2 levels are high, chances are, someone else is feeling bad as well. This means that it may be worth mentioning to a teacher or staff member. They can find out what is wrong and fix it. Of course, this can happen anywhere, not just in the classroom. So whenever you’re inside, it’s a good idea to take a break every once in a while from your homework (or video games), open a window or go outside.

Did you know? One part per hundred (1/100) is more commonly referred to as one percent (%). This comes from the latin word “centum,” which means “hundred.” It is useful to use fractions to find out what 1 percent of something is: 1/100. Similarly, one part per million can be expressed as a fraction: 1/1,000,000.

Learn More!

Carbon Dioxide on Earth and on the ISS (2018)
Let's Talk Science

Carbon Dioxide (2018)
Wisconsin Department of Health Services

Earth Fact Sheet (2017)
D.R. Williams, NASA

Carbon Dioxide: OSH Answers (2017)
Canadian Centre for Occupational Health and Safety

Associations of Cognitive Function Scores with Carbon Dioxide, Ventilation, and Volatile Organic Compound Exposures in Office Workers: A Controlled Exposure Study of Green and Conventional Office Environments (2016)
J.G. Allen et al., Environmental Health Perspectives 124.

Effects of Classroom Ventilation Rate and Temperature on Students’ Test Scores (2015)
U. Haverinen-Shaughnessy & R.J. Shaughnessy, PLoS One 10.

Poor air quality in Toronto schools could impair learning environment (2015)
J. Tahirali, CTV News

Effects of ventilation rate per person and per floor area on perceived air quality, sick building syndrome symptoms, and decision‐making (2014)
R. Maddalena et al., International Journal of Indoor Environment and Health 25.
Link to abstract. Registration or subscription required to view full text.

Is CO2 an Indoor Pollutant? Direct Effects of Low-to-Moderate CO2 Concentrations on Human Decision-Making Performance (2012)
U. Satish et al., Environmental Health Perspectives 120.

Carbon Dioxide in Indoor Air (2010)
National Collaborating Centre for Environmental Health

Human Health Risk Assessment of CO2: Survivors of Acute High-Level Exposure and Populations Sensitive to Prolonged Low-level Exposure (2004)
S.A. Rice & S.A. Rice and Associates, Third Annual Conference on Carbon Sequestration.

Indoor Air Quality, Scientific Findings Resource Bank
Berkeley Lab

Bryan Ng

Bryan Ng

Originally from Calgary, AB, my passion for science began in high school and lead me to the University of British Columbia where I am currently pursuing a Doctor of Pharmacy (PharmD) degree. Science and technology excites me because of the constant evolution and production of ideas. I am particularly interested in neuroscience. It amazes me how the brain stores info and produces the world around us - and also lets me enjoy things such as reading and exercising in my spare time!







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