What is the difference between carbon monoxide (CO) and carbon dioxide (CO2)?

What is the difference between carbon monoxide (CO) and carbon dioxide (CO2)?

What is the difference between carbon monoxide (CO) and carbon dioxide (CO2)?
What is the difference between carbon monoxide (CO) and carbon dioxide (CO2)?

When combustion is complete, it requires the presence of sufficient oxygen; its result is primarily carbon dioxide. It must be remembered that combustion refers to the chemical combination of a substance with oxygen (or oxidizer), and this sometimes, but not always, involves fire. On the other hand, when combustion is incomplete, which occurs when there is limited availability of air, only half of the oxygen (one oxygen atom: CO versus two oxygen atoms: CO2) and, therefore, the fearsome carbon monoxide is formed. Carbon (CO).

Most of the CO2 released into the atmosphere comes from natural sources. These include oceans, plants, and animal respiration (including human breathing), decomposition of organic matter, forest fires, and volcanic eruptions. While the least amount of CO2 generation is anthropogenic (caused by human activity), 87% of all human-made emissions come from burning fossil fuels, such as coal, natural gas, and oil.

Likewise, industrial plants that generate hydrogen or ammonia from natural gas or large-scale organic fermentation processes to produce ethanol are some of the leading commercial sources of CO2. This gas has various applications, for example, in the food and beverage industry (soft drinks and wine preservation). Also, in the solid-state, it is known as "dry ice" and is commonly used to transport frozen food or pharmaceutical materials.

Unlike CO2, CO is not generated naturally. A known source of this gas is the "incomplete" combustion of coal, natural gas, and oil. Insufficient oxygen levels and low temperatures lead to the formation of higher percentages of CO in the combustion mixture. Although commonly unwanted, CO is used, for example, in the manufacture of metal and chemicals, as well as in the pharmaceutical industry and electronic applications.


The primary health effect is the suffocation of exposed people since it prevents the oxygenation of the blood. In the natural physiological process of respiration, the air is sucked into the alveoli by the lungs, where oxygen from the air combines with hemoglobin in the blood to form oxyhemoglobin, responsible for the transport of oxygen to the tissues. 

When CO is present, it has a higher affinity for hemoglobin, almost 250 times greater than oxygen. This is why it combines effortlessly to form carboxyhemoglobin, which prevents the correct oxygenation of the blood circulating through the tissues. If more than 50% of the hemoglobin is in the form of carboxyhemoglobin in the blood, death can occur. At low levels of exposure, CO can cause shortness of breath, nausea, and slight dizziness.

CO2 in very high concentrations leads to suffocation due to oxygen displacement. Excessive exposure (the level above 30,000 ppm) can affect the brain and cause headaches, poor concentration, dizziness, respiratory problems. However, at concentrations usually found in the external environment (300 to 400 ppm) and in the interior environment (from 600 ppm to values ​​above 2000 ppm), it is not toxic. Rather than being considered a pollutant, it is. It believes as an indicator of air quality since the primary source of emission indoors is people themselves.

Its concentration is directly related to the ventilation index of the environment in which it is present. When CO2 levels exceed 800 to 1,200 ppm indoors, many people begin to experience discomfort, headaches, tiredness, and respiratory problems, depending on concentration and duration of exposure, these symptoms are aggravated in the case of children and "charged environment" complaints occur. The most severe effects occur from 5,000 ppm, where even can occur, although these levels are not usually reached in buildings under normal conditions, they are typical of confined closed environments.

Although CO2 asphyxiation is rare, a high concentration in a confined space can be a high risk. Symptoms of mild suffocation with this gas are headache and dizziness at concentrations below 30,000 ppm. A level of 80,000 ppm can be life-threatening. For reference, OSHA (the United States Occupational Safety and Health Administration) has established an exposure limit of 5,000 ppm over 8 hours (CMP or TLV-TWA) and 30,000 ppm for 15 minutes (CMP-CPT or TLV-STEL).

The Ministry of Health indicates that more than 4,000 people require medical treatment each year in that country due to CO asphyxiation; about 200 people die annually due to it. The permissible exposure limit (PEL) determined by Res. 295/03 for this gas is 25 ppm averaged over 8 hours (CMP or TLV-TWA) and 35 ppm for short 15-minute periods (CMP-CPT or TLV-STEL). The IDLH level (Immediately dangerous for life or health) is 1,500 ppm; that is, at that concentration, the physical consequences will be safe and irreversible. Since CO, popularly known as the "silent killer," is a colorless gas that is also odorless, tasteless, and non-irritating, it is difficult to detect the first signs of hypoxia.

It is worth mentioning that a carbon monoxide detector will not necessarily measure carbon dioxide and vice versa. The sensors specific to each gas are not only accurate, but the radar location is also relevant. CO2 is heavier than air, so the instrument should be located at a lower level, close to the ground, while CO is slightly lighter than air, so the detector should be located at a higher altitude. The most important factor when selecting the appropriate instrument is to know and understand both the environment and the properties of the gas or gases to be monitored.