Seasonal and latitudinal variation of ¹⁴CO and the tropospheric concentration of OH radicals

Abstract

Ground‐based measurements of the concentration of 14 CO are reported. The data exhibit a well‐defined seasonal variation at mid‐latitudes with a maximum of 25 ± 2 molecule cm −3 during winter and a minimum of 11 ± 1 molecule cm −3 during summer. The measurements also indicate a strong latitudinal variation, with the lower concentrations occurring in the tropics. The data are interpreted using a 2‐D time‐dependent model. To balance the sources of both 14 CO and 12 CO, an average tropospheric OH concentration of (6.5 ‐2 +3 ) × 10 5 molecule cm −3 is required. In addition, the 12 CO production rate from biological processes including the oxidation of nonmethane hydrocarbons is found to be 1250 × 10 12 g CO yr −1 .