Abstract: Method and apparatus for improved uniformity in an externally excited non-thermal chemical reaction process. In the inventive process, the reactant is externally activated for a time short compared with the time during which reactant depletion would otherwise occur. The reactant is then deactivated for a period of time comparable to the transit time across the workload. In this way improved uniformity is obtained by reducing the depletion of the reactant as it flows across the workload.