the long-path capabilities of fourier-transform infrared (ftir) spectroscopy allow field measurements of trace gas concentrations over spatial scales intermediate between those commonly used by biologists (10 cm-10 m) and climatologists (>200 km). these intermediate scale measurements are critical to relate small plot findings to data on regional dynamics obtained by remote sensing from space. both natural and agricultural environments are heterogeneous and complex. broad scale measurements that integrate the variability both spatially and temporally are needed to correctly assess biospheric/atmospheric interactions. this paper describes long-path ftir and an initial field test of the system over a 400 m optical path in a relatively uniform cotton field at the maricopa experiment station in arizona. data for water vapor, co/sub 2/ and n/sub 2/o demonstrated different responses over a 10-h period, suggesting different activities in the processes responsible for these gas emissions