Chemistry » Chemistry and the Real World » Chemical Phenomena in the Real World

Indoor Pollution: CO and CO2

Learning Objective

  • Recall how and why carbon monoxide poisoning occurs and why it can be fatal.

Key Points

  • Combustion reactions can produce both carbon monoxide and carbon dioxide, depending on the availability of oxygen.
  • Inhaled carbon monoxide competes with oxygen to bind to hemoglobin, resulting in oxygen deprivation to the organs, which can lead to death.
  • Carbon dioxide is the product of human metabolic activity and is more benign than carbon monoxide; it has few negative health effects.
  • Carbon monoxide poisoning can be prevented by installing carbon monoxide detectors that can detect unsafe levels of the toxic gas.


  • hemoglobin: the protein in red blood cells that transports oxygen from the lungs to the rest of the body; carbon monoxide can bind to it instead of oxygen

Carbon Monoxide v. Carbon Dioxide

Carbon monoxide (CO) and carbon dioxide (CO2) are both colorless, odorless gases.

Carbon monoxide: The space-filling model of carbon monoxide.

Carbon monoxide: The space-filling model of carbon monoxide.

Carbon dioxide: The space-filling model of carbon monoxide.

Carbon dioxide: The space-filling model of carbon monoxide.

Sources of Carbon Dioxide and Carbon Monoxide

Carbon dioxide and carbon monoxide are the products of combustion reactions, such as the burning of coal, wood, and natural gas, or the use of modern combustion engines (most frequently used in cars). When a hydrocarbon is burned in air, it produces carbon dioxide and water vapor. Carbon monoxide is often the product of incomplete combustion reactions. In the presence of adequate oxygen, combustion reactions will usually produce carbon dioxide. Most carbon dioxide found indoors is a result of human activity and exhalation. Carbon dioxide is also produced during cellular respiration, when humans turn glucose and oxygen into energy, water, and carbon dioxide.

Health Effects

Carbon monoxide is highly toxic. In a number of countries, carbon monoxide is a major source of air poisoning. Carbon monoxide molecules compete with oxygen to bind to hemoglobin; as a result, not enough oxygen can bind to the hemoglobin. Furthermore, carbon monoxide molecules will not detach from hemoglobin, leaving them bound to the protein for long periods of time. When oxygen can no longer circulate in the bloodstream (because most or all of the body’s hemoglobin are bound to carbon monoxide), nausea and faintness result, followed by organ failure and potentially death.

Carbon dioxide has few negative health effects relative to carbon monoxide; it has been linked to drowsiness in crowded buildings and is thought to impede education in overcrowded schools.


Carbon monoxide is particularly dangerous because it is odorless; carbon monoxide sensors can be used to alert inhabitants to rising levels of this toxic gas, however. Bans on indoor smoking are also resulting in lower indoor levels of carbon monoxide. Proper air circulation is important to prevent the accumulation of this harmful gas. Ensuring the correct installation and ventilation of heaters, furnaces, and chimneys can also prevent the buildup of carbon monoxide. Older cars can also produce carbon monoxide. Leaving a car running in a closed garage can result in potentially lethal levels of carbon monoxide; more recently-built cars do not produce dangerous levels of carbon monoxide, however, even when in an inclosed space.

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