It is clear that CO plays a central role in the chemistry of the troposphere. It carries the signature of oxidation of surface sources of CH4, NMHC and terpenoids. It is affected by anthropogenic activity. It affects the balance of HOx in the troposphere, and as we have seen this has important implications for changing amounts of radiatively active gases such as CH4 and O3. It has been determined to be increasing at 1%/year (Khalil and Rasmussen, 1988). It is important to determine the reasons for this change. Is it anthropogenic activity or part of a natural cycle?
One of the major sources of CO is oxidation of CH4. In the last 5 years it has become evident that CH4 is increasing in the atmosphere (e.g. Lowe et al., 1988). This directly impacts the production of CO and the inferences that we may deduce from an increase in CO. The sources of CO are seasonably variable and have different height distributions. Sources such as those due to slash and burn activities and photochemical oxidation of non-methane hydrocarbons (NMHC), tend to be located at the surface or in the boundary layer. Sources such as CH4 oxidation are distributed mainly in the lower troposphere. Thus to understand better the sources and sinks and seasonal behaviour of CO it is necessary to obtain a 3-D distribution of CO with time.
The provision of a 3-D field of CO mixing ratios will assist in monitoring the effects of dynamics and help to parameterize cloud transport better. A comparison of the 3-D maps provided by the MOPITT with the 3-D models will be imperative in assessing the relative magnitudes of the different sources of CO, which is a critical ingredient in the bio- geochemical carbon cycle. Global modification of OH densities due to changing levels of H2O, O3 or CO may induce changes in other levels of gases in the troposphere. Of particular importance is the possibility of affecting levels of radiatively active gases.