Carbon monoxide is produced during the incomplete combustion of hydrocarbons.
Carbon monoxide in the troposphere can be removed in three ways.
1. By reaction in the gas phase, for example with hydroxyl radicals produced by the photolysis of water molecules.
CO + OH --> CO2 + H
2. By bacteria and fungi in the soil.
2CO + O2 --> 2CO2
4CO + 2H2O --> CH4 + 3CO2
3. By plants.
CO + hf + plant leaves --> amino acids NH2CH(R)COOH
CO + plant leaves (at night) --> CO2