Carbon Dioxide vs Carbon Monoxide – What’s the difference?

In this article, we provide further insight and clarity on a commonly confused topic: the difference between carbon monoxide vs. carbon dioxide.

People often confuse carbon monoxide with carbon dioxide due to several reasons such as similarity in names, gas properties, health risks and even association. However, global media and public awareness campaigns even often confuse the two terms when encountering them in various contexts.

This is something we hope to provide further perspective on and eliminate these discrepancies for the future.

Bottom line - CO vs. CO2 What's the Difference?

• CO2 is a naturally occurring gas required for plant and animal life. CO is the result of incomplete combustion during burning.
• CO2 is a common, natural gas. CO is not.
• While fatalities from CO2 are rare, CO poisoning is one of the most common types of poisoning worldwide.

Table of Contents

CO and CO2 – What’s the Same?
CO and CO2 – What’s the Difference?
CO and CO2 Measurement
Parts per Million vs. Percentage Gas

About Carbon Dioxide
CO2 Facts
CO2 Recommended Limits

About Carbon Monoxide
CO Facts
CO Recommended Limits

CO and CO2 – What’s the same?

• Both are made from carbon and oxygen molecules
• Both are colorless, tasteless and odorless gases
• Both are in the air we breath (albeit in different concentrations)
• Both are released during combustion
• Both are important industrial gases
• Both are potentially deadly and can cause severe health problems

While they both have the word "carbon" in their name, -monoxide (mono in Greek means 1) refers to the bond between a single carbon molecule and a single oxygen molecule while -dioxide (di in Greek means 2) refers to the bond between a single carbon molecule and two oxygen molecules, (oxide means a simple compound of oxygen). In other words, CO is C+O while CO2 is O+C+O.

Both carbon dioxide and carbon monoxide are colorless, odorless and tasteless gases. However, some describe the odor of high levels of CO2 as “acidic” or “bitter.”

While both CO and CO2 are potentially deadly, this happens at vastly different concentrations. While 35 ppm (0.4%) of CO is quickly life threatening, it takes more than 30,000 ppm (3%) of CO2 to reach the same risk level.

Compressed carbon dioxide and carbon monoxide are both important industrial gases. For example, CO2 is used to carbonate beverages and to increase plant growth in indoor greenhouses. CO is used during the manufacturing of iron and nickel as well as the production of methanol. In spite of their molecular similarity, they both behave very differently when interacting with other molecules.

CO and CO2 – What’s the difference?

The most important difference is that carbon dioxide is a common, naturally occurring gas required for plant and animal life. CO is not common. It is a byproduct of the burning of fossil fuels such as oil, coal, and gas. 

CO poisoning occurs when carbon monoxide builds up in your bloodstream. Your body replaces the oxygen in your red blood cells with carbon monoxide. leading to serious tissue damage. CO2 poisoning occurs when the lungs cannot take in enough oxygen.

CO2 does not undergo oxidation reactions and is a non-flammable gas. CO undergoes oxidation reactions and is therefore a flammable gas.

• CO2 has a molar mass of about 44g/mol.
• CO has a molar mass of about 28g/mol.

Another general difference is the number of carbon and oxygen atoms. Carbon Monoxide contains one carbon and one oxygen atom, whereas carbon dioxide contains one carbon and two oxygen atoms.

What's worse carbon dioxide or carbon monoxide?

Both carbon dioxide (CO2) and carbon monoxide (CO) are very harmful when present in high concentrations, however, they do hold different levels of toxicity and effects when it comes to the environment and human health.

Carbon Dioxide Gas

Carbon dioxide is a naturally occurring gas and a significant component of Earth's atmosphere. It is produced through natural processes, such as respiration and volcanic activity, and is also a byproduct of human activities, especially the burning of fossil fuels (e.g., coal, oil, and natural gas) for energy.

• Environmental impact: Carbon dioxide is a greenhouse gas, which means it traps heat in the Earth's atmosphere, leading to the greenhouse effect. While it is necessary for maintaining Earth's temperature and supporting life, excessive CO2 emissions from human activities have led to an enhanced greenhouse effect, resulting in global warming and climate change. This contributes to issues such as rising sea levels, extreme weather events, and even disruptions to our ecosystems.
• Human health impact: Carbon dioxide is generally not toxic to humans in the concentrations typically found in the atmosphere (approximately 0.04% by volume). However, in enclosed or poorly ventilated spaces, high concentrations of CO2 can displace oxygen and cause suffocation, asphyxiation, and even fatalities.

Carbon Monoxide Gas

Carbon monoxide is a colorless, odorless, and tasteless gas produced primarily by incomplete combustion of carbon-containing fuels. Common sources include vehicle exhaust, malfunctioning home heating systems, and fires.

• Environmental impact: Carbon monoxide is not a significant greenhouse gas and does not contribute directly to global warming like carbon dioxide. However, it can indirectly affect the environment by contributing to the production of ground-level ozone, which is also harmful to both human health and the process of vegetation.

• Human health impact: Carbon monoxide is highly toxic to humans. When inhaled, it binds to hemoglobin in the blood, reducing its ability to carry oxygen, which can lead to carbon monoxide poisoning. Symptoms of CO poisoning include headaches, dizziness, weakness, nausea, and confusion. High concentrations can be fatal. Because carbon monoxide is odorless and colorless, it is particularly dangerous in enclosed spaces without proper ventilation.

In summary, both carbon dioxide and carbon monoxide have their risks and dangers, especially in confined spaces. While carbon dioxide contributes to global warming and climate change, carbon monoxide poses an immediate threat to human health. It is crucial to address both of these issues differently and reduce emissions of both gases to protect both the environment and human well-being.

CO2 vs. CO Applications

Both carbon dioxide and carbon monoxide can be found commonly used throughout many various applications and industries. Below, we highlight the main applications the gases can be found in.

Carbon dioxide

• Indoor Agriculture
• Beverage Dispensing
• Welding, Industrial
• Refrigerant, Fire Suppression
• Pharmaceutical and Laboratory

Carbon monoxide

• Automotive
• Iron and Steel Manufacturing
• Hydrogen Production
• Petrochemical 
• Food Processing
• Metallurgy - reduce pure metals from ores

Using gas detectors to measure CO and CO2

When it comes to choosing the right gas detector for the workplace, a single-gas CO detector will not measure CO2 levels, and vice-versa. Gas detectors are made with one or more gas sensors. A CO sensor cannot detect CO2. A CO2 sensor cannot detect CO.

The bright side is that there are a few options when it comes to the best gas detectors for carbon monoxide or carbon dioxide. The most important factor is that you can understand the environment that you are measuring and know what gas you will need to be monitoring.

Understanding PPM - parts per million

While large gas concentrations in a volume of air are measured in percentages, small volumes are measured in parts-per-million or parts per million (ppm) by volume (ppmv). 

When measuring small volumes, the range of concentrations is from 0 to 1,000,000, which equals 0-100%. Every 10,000 ppm equals 1% concentration.  For example, instead of saying "1% gas by volume," scientists will say "10,000 ppm." This is because 10,000 / 1,000,000 = 1%.

Why use ppm? This is because it is easier to write that the CO2 level in a room has risen from 400 ppm to 859 ppm than to explain that the CO2 level has risen from 0.04% to 0.0859%. However, both are correct. Conversely, when measuring gases above 10,000ppm it is simpler to write 1%.

Read more about parts-per-million here.

About CO2 - Carbon Dioxide

Carbon dioxide (CO2) is a colorless, odorless and tasteless gas. It is nonflammable at room temperature. The linear molecule of a carbon atom that is doubly bonded to two oxygen atoms, O=C=O. 

Where does CO2 come from?

CO2 is a naturally occurring gas in earths atmosphere. It is naturally produced by the decomposition of organic matter. It is also naturally produced by animal and human respiration, which takes in oxygen and exhales CO2. Plants and trees depend on CO2 for life (they take in CO2 and give out oxygen). 

Carbon dioxide can also be produced through industrial processes. For example, industrial plants that produce hydrogen or ammonia from natural gases are some of the largest commercial producers of carbon dioxide. 

Solid carbon dioxide is also known as "dry ice." An interesting fact about CO2 is that it coverts directly from a solid to a gas at -78°C or above. 

While not as deadly as carbon monoxide, high levels of CO2 in an enclosed space – for example, in a submarine – can suffocate you long before the oxygen runs out. In fact, dozens of people die or are injured each year as the result of CO2 leaks in bars, restaurants or in unventilated keg coolers when a beer line is left open. Others die in dry ice (frozen carbon dioxide) storage lockers used for temporary food storage.

For protection from CO2 in enclosed spaces, CO2Meter offers CO2 safety alarms.

CO2 Facts

• CO2 is a common gas in the atmosphere and is required for plant life
• CO2 is a natural byproduct of human and animal respiration, fermentation, chemical reactions, and the decomposition of plant and animal life.
• In the atmosphere CO2 measures approximately 400 ppm (parts per million). 
• CO2 is non-flammable, with no explosive properties
• CO2 poisoning is rare; however scuba divers have to watch out for it (the bends)
• Leaking pressurized CO2 tanks in enclosed areas can be dangerous for occupants - both from high levels of CO2 and from lower levels of oxygen (See oxygen displacement / asphyxiation).

CO2 Recommended Limits

• 410 ppm is the current average CO2 level on the planet
• ASHRAE recommends a 1,000 ppm limit for office buildings and classrooms to ensure overall health and performance
• OSHA limits workplace exposure levels to 5,000 ppm time-weighted average (over 8 hours)
• Drowsiness can occur at 10,000 ppm (1%) – common in closed cars or auditoriums
• Symptoms of mild CO2 poisoning include headaches and dizziness at concentrations less than 30,000 ppm (3%)
• At 40,000 ppm (4%) or above CO2 can be life-threatening

About CO - Carbon Monoxide

Like carbon dioxide, carbon monoxide is also a colorless, odorless, and tasteless gas - that is toxic and has the molecular formula CO. Many refer to carbon monoxide (CO) as one of the most dangerous gases. 

Where does CO come from?

Carbon monoxide is the result of incomplete combustion. This happens when there is a limited supply of oxygen available. 

While not normally occurring in nature, CO is a commercially important chemical, and is the result of oxygen-starved combustion from improperly ventilated fuel-burning motors and appliances like:

• Oil and gas furnaces
• Gas water heaters or gas ovens
• Gas or kerosene space heaters
• Fire places and wood stoves
• Portable generators
• Older autos without catalytic converters 

Too much carbon monoxide in an unventilated space is deadly.

In fact, carbon monoxide poisoning is the most common type of fatal poisoning worldwide. This is why many new homes are built with CO detectors in addition to smoke detectors. 

CO Facts

• CO is almost entirely a man-made gas that is not normally found in the earth's atmosphere. 
• CO is produced at dangerous levels by oxygen-starved combustion in improperly ventilated fuel-burning appliances such as generators, oil and gas furnaces, gas water heaters, gas ovens, gas or kerosene space heaters, fireplaces, and stoves
• The highest CO emissions are produced by internal combustion engines without a catalytic converter.
• CO can be a flammable gas in higher concentrations (sometimes referred to as C1D1 or C2D2 environments). Devices to measure carbon monoxide in these concentrations are often designed to be explosion-proof.
• CO is the most common type of fatal poisoning in the world.

CO Recommended Limits

• Symptoms of mild CO poisoning include headaches, dizziness, and violent vomiting at concentrations less than 100 ppm
• 0.1 ppm is the current average CO level on the planet
• 9-50 ppm is the standard maximum limit for an 8-hour workday
• 200-400ppm will result in physical symptoms followed by unconsciousness and death within hours
• Concentrations above 800 ppm can be life-threatening in minutes

See our carbon monoxide safety levels chart here.

For additional information on CO or CO2 measurement contact our technical sales team or visit our dedicated product category pages for carbon dioxide and carbon monoxide detectors.