A radiative-convective-photochemical model that extends from 0 to 53 km is used to examine the effect on atmospheric constituents and thermal structure of changes in the atmospheric levels of CO2, CFM's, CO, N2O, and combinations of these species. Calculations were carrid out for two reference atmospheres, one with high (HINOX) and one with low (LONOX) levels of NOx. The HINOX atmosphere has a vertical distribution of NOx similar to that resulting from recently published measurements. Such a distribution requires an unrealistically large value for the integrated tropospheric source of NOx. This suggests that the HINOX profile, and the measurements from which it was drawn, are more characteristic of contaminated, rather than clean, air masses. The HINOX troposphere provides a net photochemical source of O3 and is not greatly sensitive to downward transport of O3 from the stratosphere. The LONOX troposphere is a photochemical sink for O3 and, as a result, is sensitive to such variations in downward transport. Results of this study suggest that (1) infrared opacity changes due to CO2 and CFM increases can cause significant changes in tropospheric O3, OH, CH4, CO, and other species through changes in tropospheric water vapor; (2) perturbation or sensitivity studies conducted with tropospheric photochemical models may be subject to significant errors due to the absence of modulating effects provided by the stratosphere; (3) response to given perturbations is significantly dependent upon the tropospheric NOx distribution present in the model; (4) CO2 growth rates must be included in the calculation of CFM-O3 time scenarios and must account for surface temperature changes, especially in the steady state; and (5) that thermal or chemical perturbations introduce a variety of coupling or interactive mechanisms which are significant and which may provide compensating effects.