CO and CO2 – What’s the difference?

co co2 difference

CO - carbon monoxide and CO2 - carbon dioxide are often confused. The names sound the same, they both are colorless and odorless gases, and at high concentrations, both can be deadly. The difference is that CO2 is a common, naturally occurring gas required for all plant and animal life. CO is not common. It is most often a byproduct of the oxygen-starved combustion of fuel.

The media often adds to the confusion. In the past, we heard stories of suicide by sticking a garden hose in a car's tailpipe and window, then gunning the motor till the CO (carbon monoxide) put the car's occupant to sleep. Today we are told our car’s tailpipe is a major source of the "deadly" greenhouse gas CO2. It's easy to see why they are confused.

It is helpful to understand the similarities and differences between CO and CO2:

About Carbon Monoxide

  • CO is produced naturally in trace amounts by the partial oxidation of methane in the atmosphere, volcanoes and forest fires
  • CO is produced at dangerous levels by oxygen-starved combustion in improperly ventilated fuel-burning appliances such as oil and gas furnaces, gas water heaters, gas ovens, gas or kerosene space heaters, fire places and wood stoves 
  • CO is produced at dangerous levels by internal combustion engines that DO NOT use a catalytic converter
  • It is the most common type of fatal poisoning in the world

CO Recommended Levels

  • 0.1 ppm is the current average CO level on the planet
  • OSHA limits long-term workplace exposure levels to 50 ppm (parts per million)
  • Symptoms of mild CO poisoning include headaches and dizziness at concentrations less than 100 ppm
  • Concentrations as low as 700 ppm can be life-threatening

About Carbon Dioxide

  • 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 combustion of fossil fuels and wood
  • CO2 is non-flammable
  • CO2 is generated by internal combustion engines that DO use a catalytic converter
  • 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 relatively lower levels of oxygen (displacement)

CO2 Recommended Levels

  • 400 ppm is the current average CO2 level on the planet
  • ASHRAE recommends a 1,000 ppm limit for office buildings and classrooms
  • OSHA limits long-term workplace exposure levels to 5,000 ppm
  • Drowsiness can occur at 10,000 ppm – common in closed cars or auditoriums
  • Symptoms of mild CO2 poisoning include headaches and dizziness at concentrations less than 30,000 ppm (3%)
  • At 80,000 ppm (8%) CO2 can be life-threatening

What are the similarities between CO and CO2?

  • Carbon and oxygen combine to form both gases
  • Both are colorless, tasteless and odorless
  • Both are in the air worldwide (albeit in different concentrations)
  • Both are released during combustion or fire

Understanding PPM - parts per million

Parts-per-million (ppm or ppmv) is the way small numbers of molecules of gas in the air are measured by scientists since there is much less than 1% of the gas molecules by volume. Instead of saying "1% gas by volume," scientists will say "10,000 ppmv" (10,000 / 1,000,000 = 1%) or shorten it to "10,000 ppm."

For example, It is easier write that the CO2 level in a room has risen from 400 ppm to 859 ppm than to write the CO2 level has risen from 0.04% to 0.0859%. However, both are correct.

Read more about parts-per-million here.

How Monoxide and Dioxide Got their Names

You can thank the ancient Greeks for giving us their names for numerals:

• mono = 1
• di = 2
• tri = 3
• tetra = 4
• penta = 5
• hexa = 6
• hepta = 7
• octa = 8
• ennea = 9
• deca = 10

This is how we get English words like triangle (3 sides), the US Pentagon (a 5 sided-building) or decathlon (10 contests). So the first half of monoxide means 1 oxygen atom, and the first half of dioxide means 2 oxygen atoms.

For the second half of the word, we have oxide. Oxide is the name for a simple compound of oxygen with another element or group. For example, add oxygen to the element hydrogen and you get hydrogen dioxide (H20), or water. Other oxides you may have heard of are nitrous oxide (NO2 - laughing gas), or zinc oxide (ZnO - the active ingredient in sunscreen).

Source: Wikipedia


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