Carbon monoxide: natural sources dwarf man's output.
D000397:Air Pollution; D002247:Carbon Isotopes; D002248:Carbon Monoxide / Q000032:analysis*; D002734:Chlorophyll / Q000378:metabolism; D008697:Methane; D009656:North America; D010103:Oxygen Isotopes; D012621:Seasons
D002247:Carbon Isotopes; D010103:Oxygen Isotopes; D002734:Chlorophyll; D002248:Carbon Monoxide; D008697:Methane