CO₂ concentration was monitored within the FACE array at various time intervals, ranging from 0.1 second to approximately 70 minutes. The data were analyzed to search for periodicity and for evidence of "machine induced" effects; structure observed in the high frequency data appears consistent with turbulent dispersion in an ambient environment. In addition, the magnitude and duration of concentration deviations from a mean value were calculated. Fewer than 10% of such deviations extended for periods greater than 60 seconds. Furthermore few periods exhibited values of average concentration that varied by more than 100 ppm from the mean.

The ambient CO₂ level was observed over untreated portions of the field at locations removed from the FACE arrays for information on diurnal and seasonal variation. The variability in these data showed considerable dependence on wind speed, similar to observations in the FACE system, and may account for at least some of the variability present in the FACE results.