NONLINEARITIES IN THE GAS-PHASE CHEMISTRY OF THE TROPOSPHERE - OSCILLATING CONCENTRATIONS IN A SIMPLIFIED MECHANISM

The nonlinear coupling of atmospheric trace constituents can, at least in principle, cause concentrations to oscillate with time. This is de monstrated for a simplified scheme encompassing only the tropospheric gas phase chemistry of CO, O-3, HOx, and NOx. Oscillating concentratio ns with a common period of about 33 days were found for all chemical c ompounds under the forcing by time independent sources for CO and NO. Linear stability analysis shows that the periodic solution is locally stable. The periodicity is found for a large domain of NO and CO sourc e strengths. The presence of methane destroys the oscillation. This fi nding limits the applicability for problems of the real atmosphere. Th e source strengths of NO and CO necessary to produce undamped oscillat ions in the model are much larger than the corresponding globally aver aged source strengths. In the polluted boundary layer, however, the so urce strengths of NO and CO could very well be encountered. Evaluation of the Lyapunov exponents and of the dependence on the initial condit ions indicates that the periodic solution is attained independent of t he initial conditions, usually within a few days. Thus even if the met eorological and source strength conditions do not persist for the time of a whole period, parts of it may still be observable.