What is carbon dioxide?

At room temperature, carbon dioxide (CO₂) is a colorless, odorless gas formed from carbon and oxygen atoms. The fourth most common gas found in the earth’s atmosphere next to nitrogen, oxygen, and argon, CO₂ can also be liquid or solid. In its solid form, CO₂ is known as dry ice.¹

Carbon dioxide a natural part of the Earth’s carbon cycle, which is the circulation of carbon between the atmosphere, plants, animals, soils, and oceans. Humans, animals, fungi, and microorganisms produce CO₂ and plants absorb it.

However, human activity since the industrial era has significantly increased levels of CO₂ and altered this cycle, decreasing the ability of natural carbon sinks like forests to remove it from the atmosphere. Carbon dioxide is now best known as the primary greenhouse gas emitted through human activity.

Where does it come from?

Human-made carbon dioxide is primarily produced through burning fossil fuels such as oil, coal, and natural gas. Some main sources of emissions globally include transport, industry, and fuel burning for electricity and heating.

Carbon dioxide is also produced through natural sources such as animals, volcanoes, oceans, soils, and decaying plants.

One model exploring the carbon footprint of 13,000 cities indicated that emissions are highly concentrated within a limited number of affluent cities and suburbs.² The top ten cities listed included:

• Seoul, South Korea
• Guangzhou, China
• New York City, U.S.
• Hong Kong SAR, China
• Los Angeles, U.S.
• Shanghai, China
• Singapore
• Chicago, U.S.
• Tokyo / Yokohama Japan
• Riyadh, Saudi Arabia

How does it affect your health?

Carbon dioxide can build up indoors if rooms are not well-ventilated. Though relatively nontoxic and noncombustible, CO₂ can pose a number of serious health concerns.³

High indoor CO₂ concentrations can lead to:

• feeling lethargic
• clumsiness
• emotional upset
• headaches,
• difficulty concentrating
• dizziness
• vomiting
• nausea

Higher concentrations (e.g., >5000ppm over a few hours) can provoke increased heart rate, elevated blood pressure, or, in extreme cases, coma, asphyxia, and convulsions. Prolonged lack of oxygen can also permanently damage organs, including the heart and brain.

Physical activity can speed up symptoms.⁴ When you exercise, your body uses more oxygen and increases carbon dioxide production. Carbon dioxide is circulated in the bloodstream to the lungs, and that circulation is increased during exercise to send oxygen to the muscles so they can continue movement.

Indirect health effects can also be drawn from CO₂’s contribution to climate change, which is predicted to negatively impact air quality and may thus aggravate the adverse health effects associated with increased pollutants (such as ozone and particle pollution).

What are carbon dioxide’s environmental effects?

As the primary greenhouse gas contributing to global warming and climate change, CO₂ bears significant environmental impacts.

CO₂ is a ‘heat-trapping’ gas, in that it limits the heat radiation that reaches the Earth from being reflected back away again. CO₂ and other greenhouse gases contribute to the “greenhouse effect”, trapping more and more heat in the Earth’s atmosphere instead of reflecting the heat away.

Increasing global temperatures can have dire consequences for our planet and environment. A few of the consequences include:

• rising sea levels
• increased likelihood of droughts and wildfires
• species loss and ecosystem damage.

Awareness of the dramatic, negative environmental effects of increased carbon emissions have led to a global effort to try to reduce these. In many cases, reducing the sources of carbon emissions (e.g., fossil fuel combustion) will also help reduce levels of ambient air pollution, as they are often produced from the same sources.

How can you monitor CO₂ in your home or office?

The IQAir AirVisual Series air quality monitors can measurePM2.5 and CO₂ pollution which can detect 400-10,000 ppm (parts per million). Both pollutants can reach high levels indoor.

Monitoring both pollutants will allow you to balance your response to high PM2.5 and CO₂ levels. If CO₂ levels indoors are high, you may want to open your windows. Outdoor air can dilute and reduce buildup of contaminants.

Indoor air quality can suffer in winter due to reduced air exchange, especially in energy-efficient homes. Air enters the home through infiltration or ventilation. Infiltration is the natural flow of air into the home, while ventilation is a more deliberate airflow change. Opening a window is a natural means of ventilation, but there are four mechanical means of providing better ventilation to a building: 

• exhaust ventilation: often a single large fan expelling air from a building
• supply ventilation: consists of a fan and ducts
• balanced ventilation: systems combining supply and exhaust ventilation
• energy recovery ventilation: systems that heat or cool outside air as it enters

There’s both a financial and a human cost to air pollution. To see how the health and economic costs of air pollution outweigh reduction expenses, see our Cost of Air Pollution counter.