Our article confronts the question of how to accurately measure fluxes of volatile chemicals between the earth's surface and the atmosphere when the possibility of using high-frequency analyzers, such as with eddy covariance techniques, is non-existent. By subsampling and averaging publically available data from FLUXNET and applying the modified Bowen ratio method (MBR), we have determined that the MBR can work when using prolonged sampling times and single average estimates of eddy diffusivity.