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 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’s important that you understand the difference between CO and CO2:
Parts-per-million is the way small numbers of molecules of gas in the air are typically measured, since their is much less than 1% of the molecules by volume. At 1% gas by volume, scientists will instead say 10,000ppm (10,000 / 1,000,000 = 1%). For example, It is easier write that the CO2 level in a room has risen from 400ppm to 859ppm than to write the CO2 level has risen from 0.04% to 0.0859%. However, both are correct.
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).