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From what concentration does CO2 does it become a pollutant directly affecting human health?
The constant increase in the concentration of carbon dioxide in the air is harmful to our planet and is largely responsible for global warming. But from what concentration does CO2 ambient directly harm the human body?
First, note that CO2 is not a poison in itself. It is a by-product of our metabolism as well as a gas that is strongly involved in the biological activity of terrestrial fauna and flora.
Human metabolism generates CO2. The cells produce this gas, which then passes through the blood vessels to reach the lungs. Subsequently, exhalation allows us to evacuate it into the ambient air.
Outside, the concentration of CO2 amounts to approximately 400 parts per million (ppm), or 0.04% of ambient air. In large urban centres, where there are many sources of emissions, it can go up to 500 or 600 ppm.
Inside buildings, humans produce CO2. A defective ventilation system, a crowded room or tobacco smoke can lead to very high concentrations and therefore have an adverse effect on health.
From 1000 to 1500ppm, a feeling of discomfort begins to be felt. The ability to concentrate decreases and the feeling of fatigue increases.
A study from the scientific journal EEnvironmental Health Perspectives compared the cognitive performance of participants exposed to different ambient concentrations of CO2. The tests were first carried out in a well-ventilated room where the carbon dioxide concentration was 600 ppm. Then, the participants repeated the same exercises in rooms where the CO2 ambient was at 1000 ppm, then again in a room at 2500 ppm.
At 1000 ppm, cognitive performance deteriorated significantly for six of the nine exercises. At 2500 ppm, the decrease in performance is said to be “substantial” in seven of the nine activities. The exercises assessing the capacity for initiative and the development of basic strategies have reached a level deemed “dysfunctional”. In short, from 1000 ppm, cognitive abilities diminish.
To give an idea of exposure to CO2 in daily life, in Quebec, in February 2022, 22% of classrooms studied by the Quebec government had an average concentration of CO2 which was between 1000 and 1500 ppm, and 3.5% of the classes listed exceeded the 1500 ppm threshold.
From 2500 to 5000ppm, it is possible to feel headaches, exhaustion and drowsiness. Brain activities require more effort, according to studies listed in the Canadian Residential Indoor Air Quality Guidelines publication.
An exposure to 5000 ppm for eight hours is the limit allowed by the regulations on occupational health and safety in Quebec.
Concentrations above 5000ppm are rare and also exceed the limits of several legislations, including those of France and the United States. Severe headaches are likely to affect anyone exposed to such high concentrations.
Above 40,000 ppm, the National Institute of Occupational Safety and Health in the United States (NIOSH) determines that any room is dangerous to life and anyone exposed to it for more than 30 minutes is at risk of fainting. At 70,000 ppm, it will only take a few minutes to pass out, while at 100,000 ppm, your life is in immediate danger, according to the Centers for Disease Control and Prevention (CDC).
Carbon emission and ecology
Even though CO emissions2 were to continue briskly, it is unlikely that the air we breathe outside will ever reach a level dangerous to our health. If it had, environmental problems would have already caused far greater havoc, environmentalist Richard Norby told the magazine. Scientific American in 2018.
The rising level of CO2 in the atmosphere is therefore unlikely to have a direct effect on our health. On the other hand, global warming and the ensuing ecological crisis, yes.
Corrigendum: A previous version of this article stated that outdoors, the concentration of CO2 amounts to approximately 400 parts per million (ppm), or 0.4% of ambient air. It is more like 0.04%.