AbstractVisual observations of smoke dispersion in a wind tunnel and a computational fluid dynamics (CFD) model were used to evaluate methods of improving the performance of Free‐Air COT Enrichment (FACE) Systems for field studies of the effects of elevated CO2on vegetation. A special baffle, named an Enhanced Local Mixing (ELM) system, was observed to increase the turbulence and consequent dilution of fumigant gas in the atmosphere. Modelling results suggest that the ELM design reduces the spatial variation of fumigant gas concentration in small experimental plots. The potential reduction in CO2use and costs warrants further evaluation under Held condition