Segregation and chemical reaction rates in air quality models

The importance of the effects of inhomogeneous mixing on chemical reaction rates is illustrated using exact solutions and a second-order closure scheme for the relevant chemical kinetic equations. The effects of local segregation of reactants on the volume averaged reaction rates are stressed since, among other effects, these rates may bear importantly on the structure of the plume-in-grid modules in regional air quality models. In atmospheric chemistry scenarios involving multiple reactions and trace gas reactants the volume or ensemble averaged reaction rates in segregated systems can vary by orders of magnitude from the rates predicted for a uniformly mixed reactor system.