Carbon dioxide (CO2) is a colorless and odorless gas composed of one carbon atom and two oxygen atoms. It is a natural part of the Earth’s atmosphere and plays a crucial role in sustaining life. Carbon dioxide is produced through the combustion of organic materials, respiration, and decomposition. When humans breathe in, they do not actually need carbon dioxide, but it plays a very important role in the body’s functions. During exhalation, we breathe out the carbon dioxide produced as a result of cellular respiration, and excessive amounts in the breathing air can be harmful in many ways.
This short article discusses carbon dioxide in our daily lives, referring to it as micro-level effects. A completely different issue is the climate change caused by increased carbon dioxide emissions and concentrations, but that will not be addressed here, except for understanding units and interpreting outdoor air baseline levels.
The carbon dioxide concentration in the air, both indoors and outdoors, is typically described using the ppm scale, “parts per million,” which indicates the amount of carbon dioxide in the measured air. The scale is straightforward and easy to understand, and specific clear threshold values have been defined. However, before examining these threshold values, a brief detour into history is necessary, as the current outdoor carbon dioxide concentration is rising at an alarming rate. The ppm concentration of air in the pre-industrial era was approximately 200-280 ppm, where it had remained for hundreds of thousands of years. Then, humans began to push carbon dioxide emissions into the atmosphere through industrial activities, resulting in an outdoor carbon dioxide concentration of 424 ppm by 2024. The increase from, for example, the level in 2016 was 20 ppm, which may not seem very large, but if the current trend continues, the problem will grow and accelerate, with forecasts for 2100 predicting levels of 1000-1200 ppm. If we continue on this path and end up in the worst-case scenario, we will need to start pumping additional oxygen into indoor spaces. A rather startling scenario.
Now to the scale and everyday effects:
- 420 ppm: This is the outdoor CO2 level.
- Below 800 ppm: Acceptable, good indoor air.
- 800–1200 ppm: The air begins to feel stuffy, causing feelings of fatigue and cognitive ability deterioration.
- Above 2000 ppm: More severe symptoms such as breathing difficulties, headaches, and significant concentration problems.
- Above 5000 ppm: Extremely poor indoor air, and use of the space is prohibited.
- Above 40,000 ppm: Death from CO2 poisoning. However, such concentrations are extremely rare and occur mainly in closed spaces where industrial carbon dioxide has leaked.
How do different carbon dioxide concentrations affect people?
Learning, Concentration, and Decision-Making: At around 800-1000 ppm, there begins to be a decrease in alertness, cognitive reasoning, and decision-making ability, as well as a decline in concentration. In other words, a person makes poorer decisions and performs worse on tasks requiring reasoning and concentration. At 1400 ppm concentrations, cognitive abilities further deteriorate—basic decision-making ability by up to 25%, problem-solving by up to 50%, and general cognitive abilities, including concentration, by up to 50%. At concentrations above 2000 ppm, all activity, thinking, and concentration become very burdensome, and the air feels “thick.” Headaches can also be a symptom of poor indoor air.
Airborne Virus Transmission: During the COVID-19 pandemic, the mechanisms of virus transmission and infection were extensively studied, along with the risk levels of indoor air. It is nearly impossible to measure viruses in indoor air, but since the transmissibility and risk levels were quickly found to correlate with elevated carbon dioxide concentrations due to people’s exhaled air, correlations were quickly established for the increased risk of COVID-19 transmission at CO2 levels. In numerous studies and experiments, 1000 ppm was found to be the CO2 concentration at which the risk of airborne viruses (including, especially, COVID-19) began to sharply increase indoors. This remains a good threshold for safe indoor air if there is a person carrying and transmitting an airborne virus in the same space for longer than 45-60 minutes.
Sleep Quality: Studies have shown that elevated carbon dioxide concentrations have significant negative effects on sleep quality and overall health. Research indicates that the optimal CO2 concentration in a bedroom is below 750 ppm, and an increase above 1000 ppm can increase wakefulness and decrease sleep quality and the proportion of deep sleep.
Physical Performance, Mood, and Stress: Elevated CO2 concentrations can impair physical performance because the body does not receive enough oxygen. This can be particularly significant in sports facilities where ventilation is inadequate. Studies show that an athlete who sleeps in elevated concentrations the night before a competition is in worse condition than normal. High CO2 concentrations can also increase stress and anxiety. This is partly because high CO2 levels can cause mild breathing difficulties, activating the body’s stress response.
Each of us has surely been in an indoor situation where we only realize how poor the air was after leaving the space where we just spent an hour, for example, in a team meeting. This is the problem with carbon dioxide: the deterioration of air quality goes unnoticed because it is an odorless and invisible gas. And although the health risks are small and quickly passing, the effects can have a significant impact on daily life. A couple of examples:
- You are in a meeting, and due to poor indoor air, your cognitive abilities are 30% worse than normal. You are making important decisions and solving big or small problems while your decision-making ability is impaired due to poor indoor air.
- Your child is taking their matriculation exams, and the exam room has a CO2 concentration of 1400 ppm due to poor ventilation. Meanwhile, someone else is taking the same exam in a room with excellent ventilation. Your child has just given a 50% disadvantage in cognitive abilities and is competing for the same further education spots as those who took their exams in excellent indoor air conditions.
- Children in daycare are experiencing concentration difficulties, and naps are “taken” at concentrations above 2000 ppm. At the end of the day, you pick up a tired and angry child because indoor air particularly affects the brains and alertness of young children.
- You are enjoying an evening in a nice restaurant, and at the same time, a person a few tables away is unknowingly suffering from the flu. The restaurant’s ventilation is not functioning adequately for the number of people, and the CO2 reading rises above 1000 ppm. During a two-hour dinner, you catch the flu from the indoor air and spend the next two weeks sick and on sick leave.
- You wake up after eight hours of sleep still feeling tired and unwell. You wonder what the problem is when your smart ring says everything is okay and you did everything by the book before going to bed. The ventilation in your bedroom is not functioning, and the concentration rises above 2000 ppm during the night.
Summary: Carbon dioxide has a very dual role in our lives: it is a vital gas, but its excessive concentration causes significant harm to both individual well-being and the environment. Even small actions, such as improving ventilation and monitoring CO2 concentrations, can significantly enhance quality of life and health. Is it time to make indoor air quality visible?
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