Abstract
Carbon monoxide (CO) is a key player in the chemistry of the troposphere. It is, by far, the largest sink for the hydroxyl (OH) radical, which is the oxidizer of all reduced species in the atmosphere. In addition, chemical processes involving CO produce tropospheric ozone (O3). The sources of CO are about equally divided between anthropogenic sources (combustion of fossil fuels and biomass) and natural sources (oxidation of isoprene, methane, and other hydrocarbons). Recently, increases in the mixing ratio of CO have been observed. The increasing level of CO will have direct effects on the OH level with resulting long term effects both on tropospheric ozone production and on climate through the reduced destruction of greenhouse gases like methane.