Steady-state instability in tropospheric chemical mechanisms

Numerical simulations were used to investigate steady-state instabilities in chemical models containing the major tropospheric reactions of carbon monoxide, methane, and propane. The models all exhibit steady-state instability, in which the concentrations of chemical species cycle periodically with time. The occurrence of these oscillations is dependent on the emission rates of the primary pollutants (namely nitrogen monoxide, carbon monoxide, methane, and propane). The regions in which steady-state instability was observed were mapped as a function of these emission rates. In general, oscillations occur when the emission rates of nitrogen monoxide and organics are similar. The emission rates at which the kinetics switch between steady-state stability and instability as well as the oscillation periods within the unstable region are found to be sensitive to the yield of HOx and the rate coefficient for the OH+CO/hydrocarbon reaction. Implications for the occurrence of steady-state instabilities in the atmosphere are discussed.